btrfs_recover_relocation() invokes btrfs_join_transaction(), which joins
a btrfs_trans_handle object into transactions and returns a reference of
it with increased refcount to "trans".
When btrfs_recover_relocation() returns, "trans" becomes invalid, so the
refcount should be decreased to keep refcount balanced.
The reference counting issue happens in one exception handling path of
btrfs_recover_relocation(). When read_fs_root() failed, the refcnt
increased by btrfs_join_transaction() is not decreased, causing a refcnt
leak.
Fix this issue by calling btrfs_end_transaction() on this error path
when read_fs_root() failed.
Fixes: 79787eaab4 ("btrfs: replace many BUG_ONs with proper error handling")
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
I made a mistake with my previous fix, I assumed that we didn't need to
mess with the reloc roots once we were out of the part of relocation where
we are actually moving the extents.
The subtle thing that I missed is that btrfs_init_reloc_root() also
updates the last_trans for the reloc root when we do
btrfs_record_root_in_trans() for the corresponding fs_root. I've added a
comment to make sure future me doesn't make this mistake again.
This showed up as a WARN_ON() in btrfs_copy_root() because our
last_trans didn't == the current transid. This could happen if we
snapshotted a fs root with a reloc root after we set
rc->create_reloc_tree = 0, but before we actually merge the reloc root.
Worth mentioning that the regression produced the following warning
when running snapshot creation and balance in parallel:
BTRFS info (device sdc): relocating block group 30408704 flags metadata|dup
------------[ cut here ]------------
WARNING: CPU: 0 PID: 12823 at fs/btrfs/ctree.c:191 btrfs_copy_root+0x26f/0x430 [btrfs]
CPU: 0 PID: 12823 Comm: btrfs Tainted: G W 5.6.0-rc7-btrfs-next-58 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
RIP: 0010:btrfs_copy_root+0x26f/0x430 [btrfs]
RSP: 0018:ffffb96e044279b8 EFLAGS: 00010202
RAX: 0000000000000009 RBX: ffff9da70bf61000 RCX: ffffb96e04427a48
RDX: ffff9da733a770c8 RSI: ffff9da70bf61000 RDI: ffff9da694163818
RBP: ffff9da733a770c8 R08: fffffffffffffff8 R09: 0000000000000002
R10: ffffb96e044279a0 R11: 0000000000000000 R12: ffff9da694163818
R13: fffffffffffffff8 R14: ffff9da6d2512000 R15: ffff9da714cdac00
FS: 00007fdeacf328c0(0000) GS:ffff9da735e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055a2a5b8a118 CR3: 00000001eed78002 CR4: 00000000003606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
? create_reloc_root+0x49/0x2b0 [btrfs]
? kmem_cache_alloc_trace+0xe5/0x200
create_reloc_root+0x8b/0x2b0 [btrfs]
btrfs_reloc_post_snapshot+0x96/0x5b0 [btrfs]
create_pending_snapshot+0x610/0x1010 [btrfs]
create_pending_snapshots+0xa8/0xd0 [btrfs]
btrfs_commit_transaction+0x4c7/0xc50 [btrfs]
? btrfs_mksubvol+0x3cd/0x560 [btrfs]
btrfs_mksubvol+0x455/0x560 [btrfs]
__btrfs_ioctl_snap_create+0x15f/0x190 [btrfs]
btrfs_ioctl_snap_create_v2+0xa4/0xf0 [btrfs]
? mem_cgroup_commit_charge+0x6e/0x540
btrfs_ioctl+0x12d8/0x3760 [btrfs]
? do_raw_spin_unlock+0x49/0xc0
? _raw_spin_unlock+0x29/0x40
? __handle_mm_fault+0x11b3/0x14b0
? ksys_ioctl+0x92/0xb0
ksys_ioctl+0x92/0xb0
? trace_hardirqs_off_thunk+0x1a/0x1c
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x5c/0x280
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7fdeabd3bdd7
Fixes: 2abc726ab4 ("btrfs: do not init a reloc root if we aren't relocating")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Previously we would set the reloc root's last snapshot to transid - 1.
However there was a problem with doing this, and we changed it to
setting the last snapshot to the generation of the commit node of the fs
root.
This however broke should_ignore_root(). The assumption is that if we
are in a generation newer than when the reloc root was created, then we
would find the reloc root through normal backref lookups, and thus can
ignore any fs roots we find with an old enough reloc root.
Now that the last snapshot could be considerably further in the past
than before, we'd end up incorrectly ignoring an fs root. Thus we'd
find no nodes for the bytenr we were searching for, and we'd fail to
relocate anything. We'd loop through the relocate code again and see
that there were still used space in that block group, attempt to
relocate those bytenr's again, fail in the same way, and just loop like
this forever. This is tricky in that we have to not modify the fs root
at all during this time, so we need to have a block group that has data
in this fs root that is not shared by any other root, which is why this
has been difficult to reproduce.
Fixes: 054570a1dc ("Btrfs: fix relocation incorrectly dropping data references")
CC: stable@vger.kernel.org # 4.9+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We always search the commit root of the extent tree for looking up back
references, however we track the reloc roots based on their current
bytenr.
This is wrong, if we commit the transaction between relocating tree
blocks we could end up in this code in build_backref_tree
if (key.objectid == key.offset) {
/*
* Only root blocks of reloc trees use backref
* pointing to itself.
*/
root = find_reloc_root(rc, cur->bytenr);
ASSERT(root);
cur->root = root;
break;
}
find_reloc_root() is looking based on the bytenr we had in the commit
root, but if we've COWed this reloc root we will not find that bytenr,
and we will trip over the ASSERT(root).
Fix this by using the commit_root->start bytenr for indexing the commit
root. Then we change the __update_reloc_root() caller to be used when
we switch the commit root for the reloc root during commit.
This fixes the panic I was seeing when we started throttling relocation
for delayed refs.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
There are two bugs here, but fixing them independently would just result
in pain if you happened to bisect between the two patches.
First is how we handle the -EAGAIN from relocate_tree_block(). We don't
set error, unless we happen to be the first node, which makes no sense,
I have no idea what the code was trying to accomplish here.
We in fact _do_ want err set here so that we know we need to restart in
relocate_block_group(). Also we need finish_pending_nodes() to not
actually call link_to_upper(), because we didn't actually relocate the
block.
And then if we do get -EAGAIN we do not want to set our backref cache
last_trans to the one before ours. This would force us to update our
backref cache if we didn't cross transaction ids, which would mean we'd
have some nodes updated to their new_bytenr, but still able to find
their old bytenr because we're searching the same commit root as the
last time we went through relocate_tree_blocks.
Fixing these two things keeps us from panicing when we start breaking
out of relocate_tree_blocks() either for delayed ref flushing or enospc.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Since we're not only checking for metadata reservations but also if we
need to throttle our delayed ref generation, reorder
reserve_metadata_space() above the select_one_root() call in
relocate_tree_block().
The reason we want this is because select_reloc_root() will mess with
the backref cache, and if we're going to bail we want to be able to
cleanly remove this node from the backref cache and come back along to
regenerate it. Move it up so this is the first thing we do to make
restarting cleaner.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Here we are just searching down to the bytenr we're building the backref
tree for, and all of it's paths to the roots. These bytenrs are not
guaranteed to be anywhere near each other, so readahead just generates
extra latency.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
There are a few different ways to free roots, either you allocated them
yourself and you just do
free_extent_buffer(root->node);
free_extent_buffer(root->commit_node);
btrfs_put_root(root);
Which is the pattern for log roots. Or for snapshots/subvolumes that
are being dropped you simply call btrfs_free_fs_root() which does all
the cleanup for you.
Unify this all into btrfs_put_root(), so that we don't free up things
associated with the root until the last reference is dropped. This
makes the root freeing code much more significant.
The only caveat is at close_ctree() time we have to free the extent
buffers for all of our main roots (extent_root, chunk_root, etc) because
we have to drop the btree_inode and we'll run into issues if we hold
onto those nodes until ->kill_sb() time. This will be addressed in the
future when we kill the btree_inode.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This was pretty subtle, we default to reloc roots having 0 root refs, so
if we crash in the middle of the relocation they can just be deleted.
If we successfully complete the relocation operations we'll set our root
refs to 1 in prepare_to_merge() and then go on to merge_reloc_roots().
At prepare_to_merge() time if any of the reloc roots have a 0 reference
still, we will remove that reloc root from our reloc root rb tree, and
then clean it up later.
However this only happens if we successfully start a transaction. If
we've aborted previously we will skip this step completely, and only
have reloc roots with a reference count of 0, but were never properly
removed from the reloc control's rb tree.
This isn't a problem per-se, our references are held by the list the
reloc roots are on, and by the original root the reloc root belongs to.
If we end up in this situation all the reloc roots will be added to the
dirty_reloc_list, and then properly dropped at that point. The reloc
control will be free'd and the rb tree is no longer used.
There were two options when fixing this, one was to remove the BUG_ON(),
the other was to make prepare_to_merge() handle the case where we
couldn't start a trans handle.
IMO this is the cleaner solution. I started with handling the error in
prepare_to_merge(), but it turned out super ugly. And in the end this
BUG_ON() simply doesn't matter, the cleanup was happening properly, we
were just panicing because this BUG_ON() only matters in the success
case. So I've opted to just remove it and add a comment where it was.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We previously were relying on root->reloc_root to be cleaned up by the
drop snapshot, or the error handling. However if btrfs_drop_snapshot()
failed it wouldn't drop the ref for the root. Also we sort of depend on
the right thing to happen with moving reloc roots between lists and the
fs root they belong to, which makes it hard to figure out who owns the
reference.
Fix this by explicitly holding a reference on the reloc root for
roo->reloc_root. This means that we hold two references on reloc roots,
one for whichever reloc_roots list it's attached to, and the
root->reloc_root we're on.
This makes it easier to reason out who owns a reference on the root, and
when it needs to be dropped.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
The DEAD_RELOC_TREE flag is in place in order to avoid a use after free
in init_reloc_root, tracking the presence of reloc_root. However adding
the explicit tree references in previous patches makes the use after
free impossible because at this point we no longer have a reloc_control
set on the fs_info and thus cannot enter the function.
So move this to be coupled with clearing the root->reloc_root so we're
consistent with all other operations of the reloc root.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>
If we have an error while processing the reloc roots we could leak roots
that were added to rc->reloc_roots before we hit the error. We could
have also not removed the reloc tree mapping from our rb_tree, so clean
up any remaining nodes in the reloc root rb_tree.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ use rbtree_postorder_for_each_entry_safe ]
Signed-off-by: David Sterba <dsterba@suse.com>
We previously were checking if the root had a dead root before accessing
root->reloc_root in order to avoid a use-after-free type bug. However
this scenario happens after we've unset the reloc control, so we would
have been saved if we'd simply checked for fs_info->reloc_control. At
this point during relocation we no longer need to be creating new reloc
roots, so simply move this check above the reloc_root checks to avoid
any future races and confusion.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
If we do merge_reloc_roots() we could insert a few roots onto the dirty
subvol roots list, where we hold a ref on them. If we fail to start the
transaction we need to run clean_dirty_subvols() in order to cleanup the
refs.
CC: stable@vger.kernel.org # 5.4+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
If we fail to load an fs root, or fail to start a transaction we can
bail without unsetting the reloc control, which leads to problems later
when we free the reloc control but still have it attached to the file
system.
In the normal path we'll end up calling unset_reloc_control() twice, but
all it does is set fs_info->reloc_control = NULL, and we can only have
one balance at a time so it's not racey.
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
If we have an error while building the backref tree in relocation we'll
process all the pending edges and then free the node. However if we
integrated some edges into the cache we'll lose our link to those edges
by simply freeing this node, which means we'll leak memory and
references to any roots that we've found.
Instead we need to use remove_backref_node(), which walks through all of
the edges that are still linked to this node and free's them up and
drops any root references we may be holding.
CC: stable@vger.kernel.org # 4.9+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
In relocation, we need to locate all parent tree leaves referring to one
data extent, thus we have a complex mechanism to iterate throught extent
tree and subvolume trees to locate the related leaves.
However this is already done in backref.c, we have
btrfs_find_all_leafs(), which can return a ulist containing all leaves
referring to that data extent.
Use btrfs_find_all_leafs() to replace find_data_references().
There is a special handling for v1 space cache data extents, where we
need to delete the v1 space cache data extents, to avoid those data
extents to hang the data relocation.
In this patch, the special handling is done by re-iterating the root
tree leaf. Although it's a little less efficient than the old handling,
considering we can reuse a lot of code, it should be acceptable.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
It's no longer used following 30d40577e3 ("btrfs: reloc: Also queue
orphan reloc tree for cleanup to avoid BUG_ON()"), so just remove it.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Currently the non-prefixed version is a simple wrapper used to hide
the 4th argument of the prefixed version. This doesn't bring much value
in practice and only makes the code harder to follow by adding another
level of indirection. Rectify this by removing the __ prefix and
have only one public function to release bytes from a block reservation.
No semantic changes.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
When relocating data block groups with tons of small extents, or large
metadata block groups, there can be over 200,000 extents.
We will iterate all extents of such block group in relocate_block_group(),
where iteration itself can be kinda time-consuming.
So when user want to cancel the balance, the extent iteration loop can
be another target.
This patch will add the cancelling check in the extent iteration loop of
relocate_block_group() to make balance cancelling faster.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
When relocating a data extents with large large data extents, we spend
most of our time in relocate_file_extent_cluster() at stage "moving data
extents":
1) | btrfs_relocate_block_group [btrfs]() {
1) | relocate_file_extent_cluster [btrfs]() {
1) $ 6586769 us | }
1) + 18.260 us | relocate_file_extent_cluster [btrfs]();
1) + 15.770 us | relocate_file_extent_cluster [btrfs]();
1) $ 8916340 us | }
1) | btrfs_relocate_block_group [btrfs]() {
1) | relocate_file_extent_cluster [btrfs]() {
1) $ 11611586 us | }
1) + 16.930 us | relocate_file_extent_cluster [btrfs]();
1) + 15.870 us | relocate_file_extent_cluster [btrfs]();
1) $ 14986130 us | }
To make data relocation cancelling quicker, add extra balance cancelling
check after each page read in relocate_file_extent_cluster().
Cleanup and error handling uses the same mechanism as if the whole
process finished
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Introduce a new error injection point, should_cancel_balance().
It's just a wrapper of atomic_read(&fs_info->balance_cancel_req), but
allows us to override the return value.
Currently there are only one locations using this function:
- btrfs_balance()
It checks cancel before each block group.
There are other locations checking fs_info->balance_cancel_req, but they
are not used as an indicator to exit, so there is no need to use the
wrapper.
But there will be more locations coming, and some locations can cause
kernel panic if not handled properly. So introduce this error injection
to provide better test interface.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
relocate_tree_blocks calls get_tree_block_key for a block iff that block
has its ->key_ready equal false. Thus the BUG_ON in the latter function
cannot ever be triggered so remove it.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This function is only used in read_fs_root(), which is just a wrapper of
btrfs_get_fs_root().
For all the mentioned essential roots except log root tree,
btrfs_get_fs_root() has its own quick path to grab them from fs_info
directly, thus no need for key.offset modification.
For subvolume trees, btrfs_get_fs_root() with key.offset == -1 is
completely fine.
For log trees and log root tree, it's impossible to hit them, as for
relocation all backrefs are fetched from commit root, which never
records log tree blocks.
Log tree blocks either get freed in regular transaction commit, or
replayed at mount time. At runtime we should never hit an backref for
log tree in extent tree.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We are now using these for all roots, rename them to btrfs_put_root()
and btrfs_grab_root();
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Now that all callers of btrfs_get_fs_root are subsequently calling
btrfs_grab_fs_root and handling dropping the ref when they are done
appropriately, go ahead and push btrfs_grab_fs_root up into
btrfs_get_fs_root.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
All of relocation uses read_fs_root to lookup fs roots, so push the
btrfs_grab_fs_root() up into that helper and remove the individual
calls.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We look up the fs root in various places in here when recovering from a
crashed relcoation. Make sure we hold a ref on the root whenever we
look them up.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We're creating a reloc inode in the data reloc tree, we need to hold a
ref on the root while we're doing that.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We're looking up the data references for the bytenr in a root, we need
to hold a ref on that root while we're doing that.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We are recording this root in the transaction, so we need to hold a ref
on it until we do that.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We look up the corresponding root for the reloc root, we need to hold a
ref while we're messing with it.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We look up the reloc roots corresponding root, we need to hold a ref on
that root.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This is trickier than the previous conversions. We have backref_node's
that need to hold onto their root for their lifetime. Do the read of
the root and grab the ref. If at any point we don't use the root we
discard it, however if we use it in our backref node we don't free it
until we free the backref node. Any time we switch the root's for the
backref node we need to drop our ref on the old root and grab the ref on
the new root, and if we dupe a node we need to get a ref on the root
there as well.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Relocation has it's special roots, we don't want to save these in the
root cache either, so swap it to use btrfs_read_tree_root(). However
the reloc root does need REF_COWS set, so make sure we set it everywhere
we use this helper, as it no longer does the REF_COWS setting.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Relocation is one of the most complex part of btrfs, while it's also the
foundation stone for online resizing, profile converting.
For such a complex facility, we should at least have some introduction
to it.
This patch will add an basic introduction at pretty a high level,
explaining:
- What relocation does
- How relocation is done
Only mentioning how data reloc tree and reloc tree are involved in the
operation.
No details like the backref cache, or the data reloc tree contents.
- Which function to refer.
More detailed comments will be added for reloc tree creation, data reloc
tree creation and backref cache.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
ordered->start, ordered->len, and ordered->disk_len correspond to
fi->disk_bytenr, fi->num_bytes, and fi->disk_num_bytes, respectively.
It's confusing to translate between the two naming schemes. Since a
btrfs_ordered_extent is basically a pending btrfs_file_extent_item,
let's make the former use the naming from the latter.
Note that I didn't touch the names in tracepoints just in case there are
scripts depending on the current naming.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
There are two relocation stages but both print the same message. Add the
description of the stage. This can help debugging or provides
informative message to users.
BTRFS info (device dm-5): balance: start -d -m -s
BTRFS info (device dm-5): relocating block group 30408704 flags metadata|dup
BTRFS info (device dm-5): found 2 extents, stage: move data extents
BTRFS info (device dm-5): relocating block group 22020096 flags system|dup
BTRFS info (device dm-5): found 1 extents, stage: move data extents
BTRFS info (device dm-5): relocating block group 13631488 flags data
BTRFS info (device dm-5): found 1 extents, stage: move data extents
BTRFS info (device dm-5): found 1 extents, stage: update data pointers
BTRFS info (device dm-5): balance: ended with status: 0
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[BUG]
There are several different KASAN reports for balance + snapshot
workloads. Involved call paths include:
should_ignore_root+0x54/0xb0 [btrfs]
build_backref_tree+0x11af/0x2280 [btrfs]
relocate_tree_blocks+0x391/0xb80 [btrfs]
relocate_block_group+0x3e5/0xa00 [btrfs]
btrfs_relocate_block_group+0x240/0x4d0 [btrfs]
btrfs_relocate_chunk+0x53/0xf0 [btrfs]
btrfs_balance+0xc91/0x1840 [btrfs]
btrfs_ioctl_balance+0x416/0x4e0 [btrfs]
btrfs_ioctl+0x8af/0x3e60 [btrfs]
do_vfs_ioctl+0x831/0xb10
create_reloc_root+0x9f/0x460 [btrfs]
btrfs_reloc_post_snapshot+0xff/0x6c0 [btrfs]
create_pending_snapshot+0xa9b/0x15f0 [btrfs]
create_pending_snapshots+0x111/0x140 [btrfs]
btrfs_commit_transaction+0x7a6/0x1360 [btrfs]
btrfs_mksubvol+0x915/0x960 [btrfs]
btrfs_ioctl_snap_create_transid+0x1d5/0x1e0 [btrfs]
btrfs_ioctl_snap_create_v2+0x1d3/0x270 [btrfs]
btrfs_ioctl+0x241b/0x3e60 [btrfs]
do_vfs_ioctl+0x831/0xb10
btrfs_reloc_pre_snapshot+0x85/0xc0 [btrfs]
create_pending_snapshot+0x209/0x15f0 [btrfs]
create_pending_snapshots+0x111/0x140 [btrfs]
btrfs_commit_transaction+0x7a6/0x1360 [btrfs]
btrfs_mksubvol+0x915/0x960 [btrfs]
btrfs_ioctl_snap_create_transid+0x1d5/0x1e0 [btrfs]
btrfs_ioctl_snap_create_v2+0x1d3/0x270 [btrfs]
btrfs_ioctl+0x241b/0x3e60 [btrfs]
do_vfs_ioctl+0x831/0xb10
[CAUSE]
All these call sites are only relying on root->reloc_root, which can
undergo btrfs_drop_snapshot(), and since we don't have real refcount
based protection to reloc roots, we can reach already dropped reloc
root, triggering KASAN.
[FIX]
To avoid such access to unstable root->reloc_root, we should check
BTRFS_ROOT_DEAD_RELOC_TREE bit first.
This patch introduces wrappers that provide the correct way to check the
bit with memory barriers protection.
Most callers don't distinguish merged reloc tree and no reloc tree. The
only exception is should_ignore_root(), as merged reloc tree can be
ignored, while no reloc tree shouldn't.
[CRITICAL SECTION ANALYSIS]
Although test_bit()/set_bit()/clear_bit() doesn't imply a barrier, the
DEAD_RELOC_TREE bit has extra help from transaction as a higher level
barrier, the lifespan of root::reloc_root and DEAD_RELOC_TREE bit are:
NULL: reloc_root is NULL PTR: reloc_root is not NULL
0: DEAD_RELOC_ROOT bit not set DEAD: DEAD_RELOC_ROOT bit set
(NULL, 0) Initial state __
| /\ Section A
btrfs_init_reloc_root() \/
| __
(PTR, 0) reloc_root initialized /\
| |
btrfs_update_reloc_root() | Section B
| |
(PTR, DEAD) reloc_root has been merged \/
| __
=== btrfs_commit_transaction() ====================
| /\
clean_dirty_subvols() |
| | Section C
(NULL, DEAD) reloc_root cleanup starts \/
| __
btrfs_drop_snapshot() /\
| | Section D
(NULL, 0) Back to initial state \/
Every have_reloc_root() or test_bit(DEAD_RELOC_ROOT) caller holds
transaction handle, so none of such caller can cross transaction boundary.
In Section A, every caller just found no DEAD bit, and grab reloc_root.
In the cross section A-B, caller may get no DEAD bit, but since reloc_root
is still completely valid thus accessing reloc_root is completely safe.
No test_bit() caller can cross the boundary of Section B and Section C.
In Section C, every caller found the DEAD bit, so no one will access
reloc_root.
In the cross section C-D, either caller gets the DEAD bit set, avoiding
access reloc_root no matter if it's safe or not. Or caller get the DEAD
bit cleared, then access reloc_root, which is already NULL, nothing will
be wrong.
The memory write barriers are between the reloc_root updates and bit
set/clear, the pairing read side is before test_bit.
Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Fixes: d2311e6985 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ barriers ]
Signed-off-by: David Sterba <dsterba@suse.com>
If we fail to read the fs root corresponding with a reloc root we'll
just break out and free the reloc roots. But we remove our current
reloc_root from this list higher up, which means we'll leak this
reloc_root. Fix this by adding ourselves back to the reloc_roots list
so we are properly cleaned up.
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
We can now remove the bdev from extent_map. Previous patches made sure
that bio_set_dev is correctly in all places and that we don't need to
grab it from latest_bdev or pass it around inside the extent map.
Signed-off-by: David Sterba <dsterba@suse.com>
[BUG]
When running btrfs/072 with only one online CPU, it has a pretty high
chance to fail:
btrfs/072 12s ... _check_dmesg: something found in dmesg (see xfstests-dev/results//btrfs/072.dmesg)
- output mismatch (see xfstests-dev/results//btrfs/072.out.bad)
--- tests/btrfs/072.out 2019-10-22 15:18:14.008965340 +0800
+++ /xfstests-dev/results//btrfs/072.out.bad 2019-11-14 15:56:45.877152240 +0800
@@ -1,2 +1,3 @@
QA output created by 072
Silence is golden
+Scrub find errors in "-m dup -d single" test
...
And with the following call trace:
BTRFS info (device dm-5): scrub: started on devid 1
------------[ cut here ]------------
BTRFS: Transaction aborted (error -27)
WARNING: CPU: 0 PID: 55087 at fs/btrfs/block-group.c:1890 btrfs_create_pending_block_groups+0x3e6/0x470 [btrfs]
CPU: 0 PID: 55087 Comm: btrfs Tainted: G W O 5.4.0-rc1-custom+ #13
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:btrfs_create_pending_block_groups+0x3e6/0x470 [btrfs]
Call Trace:
__btrfs_end_transaction+0xdb/0x310 [btrfs]
btrfs_end_transaction+0x10/0x20 [btrfs]
btrfs_inc_block_group_ro+0x1c9/0x210 [btrfs]
scrub_enumerate_chunks+0x264/0x940 [btrfs]
btrfs_scrub_dev+0x45c/0x8f0 [btrfs]
btrfs_ioctl+0x31a1/0x3fb0 [btrfs]
do_vfs_ioctl+0x636/0xaa0
ksys_ioctl+0x67/0x90
__x64_sys_ioctl+0x43/0x50
do_syscall_64+0x79/0xe0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
---[ end trace 166c865cec7688e7 ]---
[CAUSE]
The error number -27 is -EFBIG, returned from the following call chain:
btrfs_end_transaction()
|- __btrfs_end_transaction()
|- btrfs_create_pending_block_groups()
|- btrfs_finish_chunk_alloc()
|- btrfs_add_system_chunk()
This happens because we have used up all space of
btrfs_super_block::sys_chunk_array.
The root cause is, we have the following bad loop of creating tons of
system chunks:
1. The only SYSTEM chunk is being scrubbed
It's very common to have only one SYSTEM chunk.
2. New SYSTEM bg will be allocated
As btrfs_inc_block_group_ro() will check if we have enough space
after marking current bg RO. If not, then allocate a new chunk.
3. New SYSTEM bg is still empty, will be reclaimed
During the reclaim, we will mark it RO again.
4. That newly allocated empty SYSTEM bg get scrubbed
We go back to step 2, as the bg is already mark RO but still not
cleaned up yet.
If the cleaner kthread doesn't get executed fast enough (e.g. only one
CPU), then we will get more and more empty SYSTEM chunks, using up all
the space of btrfs_super_block::sys_chunk_array.
[FIX]
Since scrub/dev-replace doesn't always need to allocate new extent,
especially chunk tree extent, so we don't really need to do chunk
pre-allocation.
To break above spiral, here we introduce a new parameter to
btrfs_inc_block_group(), @do_chunk_alloc, which indicates whether we
need extra chunk pre-allocation.
For relocation, we pass @do_chunk_alloc=true, while for scrub, we pass
@do_chunk_alloc=false.
This should keep unnecessary empty chunks from popping up for scrub.
Also, since there are two parameters for btrfs_inc_block_group_ro(),
add more comment for it.
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
The type name is misleading, a single entry is named 'cache' while this
normally means a collection of objects. Rename that everywhere. Also the
identifier was quite long, making function prototypes harder to format.
Suggested-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
The on-disk format of block group item makes use of the key that stores
the offset and length. This is further used in the code, although this
makes thing harder to understand. The key is also packed so the
offset/length is not properly aligned as u64.
Add start (key.objectid) and length (key.offset) members to block group
and remove the embedded key. When the item is searched or written, a
local variable for key is used.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
For unknown reasons, the member 'used' in the block group struct is
stored in the b-tree item and accessed everywhere using the special
accessor helper. Let's unify it and make it a regular member and only
update the item before writing it to the tree.
The item is still being used for flags and chunk_objectid, there's some
duplication until the item is removed in following patches.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
The helper is trivial and we can understand what the atomic_inc on
something named refs does.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
The parameter is now always set to NULL and could be dropped. The last
user was get_default_root but that got reworked in 05dbe6837b ("Btrfs:
unify subvol= and subvolid= mounting") and the parameter became unused.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[Background]
Btrfs qgroup uses two types of reserved space for METADATA space,
PERTRANS and PREALLOC.
PERTRANS is metadata space reserved for each transaction started by
btrfs_start_transaction().
While PREALLOC is for delalloc, where we reserve space before joining a
transaction, and finally it will be converted to PERTRANS after the
writeback is done.
[Inconsistency]
However there is inconsistency in how we handle PREALLOC metadata space.
The most obvious one is:
In btrfs_buffered_write():
btrfs_delalloc_release_extents(BTRFS_I(inode), reserve_bytes, true);
We always free qgroup PREALLOC meta space.
While in btrfs_truncate_block():
btrfs_delalloc_release_extents(BTRFS_I(inode), blocksize, (ret != 0));
We only free qgroup PREALLOC meta space when something went wrong.
[The Correct Behavior]
The correct behavior should be the one in btrfs_buffered_write(), we
should always free PREALLOC metadata space.
The reason is, the btrfs_delalloc_* mechanism works by:
- Reserve metadata first, even it's not necessary
In btrfs_delalloc_reserve_metadata()
- Free the unused metadata space
Normally in:
btrfs_delalloc_release_extents()
|- btrfs_inode_rsv_release()
Here we do calculation on whether we should release or not.
E.g. for 64K buffered write, the metadata rsv works like:
/* The first page */
reserve_meta: num_bytes=calc_inode_reservations()
free_meta: num_bytes=0
total: num_bytes=calc_inode_reservations()
/* The first page caused one outstanding extent, thus needs metadata
rsv */
/* The 2nd page */
reserve_meta: num_bytes=calc_inode_reservations()
free_meta: num_bytes=calc_inode_reservations()
total: not changed
/* The 2nd page doesn't cause new outstanding extent, needs no new meta
rsv, so we free what we have reserved */
/* The 3rd~16th pages */
reserve_meta: num_bytes=calc_inode_reservations()
free_meta: num_bytes=calc_inode_reservations()
total: not changed (still space for one outstanding extent)
This means, if btrfs_delalloc_release_extents() determines to free some
space, then those space should be freed NOW.
So for qgroup, we should call btrfs_qgroup_free_meta_prealloc() other
than btrfs_qgroup_convert_reserved_meta().
The good news is:
- The callers are not that hot
The hottest caller is in btrfs_buffered_write(), which is already
fixed by commit 336a8bb8e3 ("btrfs: Fix wrong
btrfs_delalloc_release_extents parameter"). Thus it's not that
easy to cause false EDQUOT.
- The trans commit in advance for qgroup would hide the bug
Since commit f5fef45936 ("btrfs: qgroup: Make qgroup async transaction
commit more aggressive"), when btrfs qgroup metadata free space is slow,
it will try to commit transaction and free the wrongly converted
PERTRANS space, so it's not that easy to hit such bug.
[FIX]
So to fix the problem, remove the @qgroup_free parameter for
btrfs_delalloc_release_extents(), and always pass true to
btrfs_inode_rsv_release().
Reported-by: Filipe Manana <fdmanana@suse.com>
Fixes: 43b18595d6 ("btrfs: qgroup: Use separate meta reservation type for delalloc")
CC: stable@vger.kernel.org # 4.19+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
If we error out when finding a page at relocate_file_extent_cluster(), we
need to release the outstanding extents counter on the relocation inode,
set by the previous call to btrfs_delalloc_reserve_metadata(), otherwise
the inode's block reserve size can never decrease to zero and metadata
space is leaked. Therefore add a call to btrfs_delalloc_release_extents()
in case we can't find the target page.
Fixes: 8b62f87bad ("Btrfs: rework outstanding_extents")
CC: stable@vger.kernel.org # 4.19+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[BUG]
One user reported a reproducible KASAN report about use-after-free:
BTRFS info (device sdi1): balance: start -dvrange=1256811659264..1256811659265
BTRFS info (device sdi1): relocating block group 1256811659264 flags data|raid0
==================================================================
BUG: KASAN: use-after-free in btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
Write of size 8 at addr ffff88856f671710 by task kworker/u24:10/261579
CPU: 2 PID: 261579 Comm: kworker/u24:10 Tainted: P OE 5.2.11-arch1-1-kasan #4
Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./X99 Extreme4, BIOS P3.80 04/06/2018
Workqueue: btrfs-endio-write btrfs_endio_write_helper [btrfs]
Call Trace:
dump_stack+0x7b/0xba
print_address_description+0x6c/0x22e
? btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
__kasan_report.cold+0x1b/0x3b
? btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
kasan_report+0x12/0x17
__asan_report_store8_noabort+0x17/0x20
btrfs_init_reloc_root+0x2cd/0x340 [btrfs]
record_root_in_trans+0x2a0/0x370 [btrfs]
btrfs_record_root_in_trans+0xf4/0x140 [btrfs]
start_transaction+0x1ab/0xe90 [btrfs]
btrfs_join_transaction+0x1d/0x20 [btrfs]
btrfs_finish_ordered_io+0x7bf/0x18a0 [btrfs]
? lock_repin_lock+0x400/0x400
? __kmem_cache_shutdown.cold+0x140/0x1ad
? btrfs_unlink_subvol+0x9b0/0x9b0 [btrfs]
finish_ordered_fn+0x15/0x20 [btrfs]
normal_work_helper+0x1bd/0xca0 [btrfs]
? process_one_work+0x819/0x1720
? kasan_check_read+0x11/0x20
btrfs_endio_write_helper+0x12/0x20 [btrfs]
process_one_work+0x8c9/0x1720
? pwq_dec_nr_in_flight+0x2f0/0x2f0
? worker_thread+0x1d9/0x1030
worker_thread+0x98/0x1030
kthread+0x2bb/0x3b0
? process_one_work+0x1720/0x1720
? kthread_park+0x120/0x120
ret_from_fork+0x35/0x40
Allocated by task 369692:
__kasan_kmalloc.part.0+0x44/0xc0
__kasan_kmalloc.constprop.0+0xba/0xc0
kasan_kmalloc+0x9/0x10
kmem_cache_alloc_trace+0x138/0x260
btrfs_read_tree_root+0x92/0x360 [btrfs]
btrfs_read_fs_root+0x10/0xb0 [btrfs]
create_reloc_root+0x47d/0xa10 [btrfs]
btrfs_init_reloc_root+0x1e2/0x340 [btrfs]
record_root_in_trans+0x2a0/0x370 [btrfs]
btrfs_record_root_in_trans+0xf4/0x140 [btrfs]
start_transaction+0x1ab/0xe90 [btrfs]
btrfs_start_transaction+0x1e/0x20 [btrfs]
__btrfs_prealloc_file_range+0x1c2/0xa00 [btrfs]
btrfs_prealloc_file_range+0x13/0x20 [btrfs]
prealloc_file_extent_cluster+0x29f/0x570 [btrfs]
relocate_file_extent_cluster+0x193/0xc30 [btrfs]
relocate_data_extent+0x1f8/0x490 [btrfs]
relocate_block_group+0x600/0x1060 [btrfs]
btrfs_relocate_block_group+0x3a0/0xa00 [btrfs]
btrfs_relocate_chunk+0x9e/0x180 [btrfs]
btrfs_balance+0x14e4/0x2fc0 [btrfs]
btrfs_ioctl_balance+0x47f/0x640 [btrfs]
btrfs_ioctl+0x119d/0x8380 [btrfs]
do_vfs_ioctl+0x9f5/0x1060
ksys_ioctl+0x67/0x90
__x64_sys_ioctl+0x73/0xb0
do_syscall_64+0xa5/0x370
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Freed by task 369692:
__kasan_slab_free+0x14f/0x210
kasan_slab_free+0xe/0x10
kfree+0xd8/0x270
btrfs_drop_snapshot+0x154c/0x1eb0 [btrfs]
clean_dirty_subvols+0x227/0x340 [btrfs]
relocate_block_group+0x972/0x1060 [btrfs]
btrfs_relocate_block_group+0x3a0/0xa00 [btrfs]
btrfs_relocate_chunk+0x9e/0x180 [btrfs]
btrfs_balance+0x14e4/0x2fc0 [btrfs]
btrfs_ioctl_balance+0x47f/0x640 [btrfs]
btrfs_ioctl+0x119d/0x8380 [btrfs]
do_vfs_ioctl+0x9f5/0x1060
ksys_ioctl+0x67/0x90
__x64_sys_ioctl+0x73/0xb0
do_syscall_64+0xa5/0x370
entry_SYSCALL_64_after_hwframe+0x44/0xa9
The buggy address belongs to the object at ffff88856f671100
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1552 bytes inside of
4096-byte region [ffff88856f671100, ffff88856f672100)
The buggy address belongs to the page:
page:ffffea0015bd9c00 refcount:1 mapcount:0 mapping:ffff88864400e600 index:0x0 compound_mapcount: 0
flags: 0x2ffff0000010200(slab|head)
raw: 02ffff0000010200 dead000000000100 dead000000000200 ffff88864400e600
raw: 0000000000000000 0000000000070007 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff88856f671600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88856f671680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88856f671700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88856f671780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88856f671800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
BTRFS info (device sdi1): 1 enospc errors during balance
BTRFS info (device sdi1): balance: ended with status: -28
[CAUSE]
The problem happens when finish_ordered_io() get called with balance
still running, while the reloc root of that subvolume is already dead.
(Tree is swap already done, but tree not yet deleted for possible qgroup
usage.)
That means root->reloc_root still exists, but that reloc_root can be
under btrfs_drop_snapshot(), thus we shouldn't access it.
The following race could cause the use-after-free problem:
CPU1 | CPU2
--------------------------------------------------------------------------
| relocate_block_group()
| |- unset_reloc_control(rc)
| |- btrfs_commit_transaction()
btrfs_finish_ordered_io() | |- clean_dirty_subvols()
|- btrfs_join_transaction() | |
|- record_root_in_trans() | |
|- btrfs_init_reloc_root() | |
|- if (root->reloc_root) | |
| | |- root->reloc_root = NULL
| | |- btrfs_drop_snapshot(reloc_root);
|- reloc_root->last_trans|
= trans->transid |
^^^^^^^^^^^^^^^^^^^^^^
Use after free
[FIX]
Fix it by the following modifications:
- Test if the root has dead reloc tree before accessing root->reloc_root
If the root has BTRFS_ROOT_DEAD_RELOC_TREE, then we don't need to
create or update root->reloc_tree
- Clear the BTRFS_ROOT_DEAD_RELOC_TREE flag until we have fully dropped
reloc tree
To co-operate with above modification, so as long as
BTRFS_ROOT_DEAD_RELOC_TREE is still set, we won't try to re-create
reloc tree at record_root_in_trans().
Reported-by: Cebtenzzre <cebtenzzre@gmail.com>
Fixes: d2311e6985 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots")
CC: stable@vger.kernel.org # 5.1+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
