linux/fs/btrfs/async-thread.h

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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2007 Oracle. All rights reserved.
* Copyright (C) 2014 Fujitsu. All rights reserved.
*/
#ifndef BTRFS_ASYNC_THREAD_H
#define BTRFS_ASYNC_THREAD_H
Btrfs: fix task hang under heavy compressed write This has been reported and discussed for a long time, and this hang occurs in both 3.15 and 3.16. Btrfs now migrates to use kernel workqueue, but it introduces this hang problem. Btrfs has a kind of work queued as an ordered way, which means that its ordered_func() must be processed in the way of FIFO, so it usually looks like -- normal_work_helper(arg) work = container_of(arg, struct btrfs_work, normal_work); work->func() <---- (we name it work X) for ordered_work in wq->ordered_list ordered_work->ordered_func() ordered_work->ordered_free() The hang is a rare case, first when we find free space, we get an uncached block group, then we go to read its free space cache inode for free space information, so it will file a readahead request btrfs_readpages() for page that is not in page cache __do_readpage() submit_extent_page() btrfs_submit_bio_hook() btrfs_bio_wq_end_io() submit_bio() end_workqueue_bio() <--(ret by the 1st endio) queue a work(named work Y) for the 2nd also the real endio() So the hang occurs when work Y's work_struct and work X's work_struct happens to share the same address. A bit more explanation, A,B,C -- struct btrfs_work arg -- struct work_struct kthread: worker_thread() pick up a work_struct from @worklist process_one_work(arg) worker->current_work = arg; <-- arg is A->normal_work worker->current_func(arg) normal_work_helper(arg) A = container_of(arg, struct btrfs_work, normal_work); A->func() A->ordered_func() A->ordered_free() <-- A gets freed B->ordered_func() submit_compressed_extents() find_free_extent() load_free_space_inode() ... <-- (the above readhead stack) end_workqueue_bio() btrfs_queue_work(work C) B->ordered_free() As if work A has a high priority in wq->ordered_list and there are more ordered works queued after it, such as B->ordered_func(), its memory could have been freed before normal_work_helper() returns, which means that kernel workqueue code worker_thread() still has worker->current_work pointer to be work A->normal_work's, ie. arg's address. Meanwhile, work C is allocated after work A is freed, work C->normal_work and work A->normal_work are likely to share the same address(I confirmed this with ftrace output, so I'm not just guessing, it's rare though). When another kthread picks up work C->normal_work to process, and finds our kthread is processing it(see find_worker_executing_work()), it'll think work C as a collision and skip then, which ends up nobody processing work C. So the situation is that our kthread is waiting forever on work C. Besides, there're other cases that can lead to deadlock, but the real problem is that all btrfs workqueue shares one work->func, -- normal_work_helper, so this makes each workqueue to have its own helper function, but only a wraper pf normal_work_helper. With this patch, I no long hit the above hang. Signed-off-by: Liu Bo <bo.li.liu@oracle.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-08-15 15:36:53 +00:00
#include <linux/workqueue.h>
struct btrfs_fs_info;
struct btrfs_workqueue;
struct btrfs_work;
typedef void (*btrfs_func_t)(struct btrfs_work *arg);
struct btrfs_work {
btrfs_func_t func;
btrfs_func_t ordered_func;
btrfs_func_t ordered_free;
/* Don't touch things below */
struct work_struct normal_work;
struct list_head ordered_list;
struct btrfs_workqueue *wq;
unsigned long flags;
};
struct btrfs_workqueue *btrfs_alloc_workqueue(struct btrfs_fs_info *fs_info,
const char *name,
unsigned int flags,
int limit_active,
int thresh);
void btrfs_init_work(struct btrfs_work *work, btrfs_func_t func,
btrfs_func_t ordered_func, btrfs_func_t ordered_free);
void btrfs_queue_work(struct btrfs_workqueue *wq,
struct btrfs_work *work);
void btrfs_destroy_workqueue(struct btrfs_workqueue *wq);
void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int max);
struct btrfs_fs_info * __pure btrfs_work_owner(const struct btrfs_work *work);
struct btrfs_fs_info * __pure btrfs_workqueue_owner(const struct btrfs_workqueue *wq);
bool btrfs_workqueue_normal_congested(const struct btrfs_workqueue *wq);
Btrfs: fix crash during unmount due to race with delayed inode workers During unmount we can have a job from the delayed inode items work queue still running, that can lead to at least two bad things: 1) A crash, because the worker can try to create a transaction just after the fs roots were freed; 2) A transaction leak, because the worker can create a transaction before the fs roots are freed and just after we committed the last transaction and after we stopped the transaction kthread. A stack trace example of the crash: [79011.691214] kernel BUG at lib/radix-tree.c:982! [79011.692056] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI [79011.693180] CPU: 3 PID: 1394 Comm: kworker/u8:2 Tainted: G W 5.6.0-rc2-btrfs-next-54 #2 (...) [79011.696789] Workqueue: btrfs-delayed-meta btrfs_work_helper [btrfs] [79011.697904] RIP: 0010:radix_tree_tag_set+0xe7/0x170 (...) [79011.702014] RSP: 0018:ffffb3c84a317ca0 EFLAGS: 00010293 [79011.702949] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [79011.704202] RDX: ffffb3c84a317cb0 RSI: ffffb3c84a317ca8 RDI: ffff8db3931340a0 [79011.705463] RBP: 0000000000000005 R08: 0000000000000005 R09: ffffffff974629d0 [79011.706756] R10: ffffb3c84a317bc0 R11: 0000000000000001 R12: ffff8db393134000 [79011.708010] R13: ffff8db3931340a0 R14: ffff8db393134068 R15: 0000000000000001 [79011.709270] FS: 0000000000000000(0000) GS:ffff8db3b6a00000(0000) knlGS:0000000000000000 [79011.710699] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [79011.711710] CR2: 00007f22c2a0a000 CR3: 0000000232ad4005 CR4: 00000000003606e0 [79011.712958] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [79011.714205] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [79011.715448] Call Trace: [79011.715925] record_root_in_trans+0x72/0xf0 [btrfs] [79011.716819] btrfs_record_root_in_trans+0x4b/0x70 [btrfs] [79011.717925] start_transaction+0xdd/0x5c0 [btrfs] [79011.718829] btrfs_async_run_delayed_root+0x17e/0x2b0 [btrfs] [79011.719915] btrfs_work_helper+0xaa/0x720 [btrfs] [79011.720773] process_one_work+0x26d/0x6a0 [79011.721497] worker_thread+0x4f/0x3e0 [79011.722153] ? process_one_work+0x6a0/0x6a0 [79011.722901] kthread+0x103/0x140 [79011.723481] ? kthread_create_worker_on_cpu+0x70/0x70 [79011.724379] ret_from_fork+0x3a/0x50 (...) The following diagram shows a sequence of steps that lead to the crash during ummount of the filesystem: CPU 1 CPU 2 CPU 3 btrfs_punch_hole() btrfs_btree_balance_dirty() btrfs_balance_delayed_items() --> sees fs_info->delayed_root->items with value 200, which is greater than BTRFS_DELAYED_BACKGROUND (128) and smaller than BTRFS_DELAYED_WRITEBACK (512) btrfs_wq_run_delayed_node() --> queues a job for fs_info->delayed_workers to run btrfs_async_run_delayed_root() btrfs_async_run_delayed_root() --> job queued by CPU 1 --> starts picking and running delayed nodes from the prepare_list list close_ctree() btrfs_delete_unused_bgs() btrfs_commit_super() btrfs_join_transaction() --> gets transaction N btrfs_commit_transaction(N) --> set transaction state to TRANTS_STATE_COMMIT_START btrfs_first_prepared_delayed_node() --> picks delayed node X through the prepared_list list btrfs_run_delayed_items() btrfs_first_delayed_node() --> also picks delayed node X but through the node_list list __btrfs_commit_inode_delayed_items() --> runs all delayed items from this node and drops the node's item count to 0 through call to btrfs_release_delayed_inode() --> finishes running any remaining delayed nodes --> finishes transaction commit --> stops cleaner and transaction threads btrfs_free_fs_roots() --> frees all roots and removes them from the radix tree fs_info->fs_roots_radix btrfs_join_transaction() start_transaction() btrfs_record_root_in_trans() record_root_in_trans() radix_tree_tag_set() --> crashes because the root is not in the radix tree anymore If the worker is able to call btrfs_join_transaction() before the unmount task frees the fs roots, we end up leaking a transaction and all its resources, since after the call to btrfs_commit_super() and stopping the transaction kthread, we don't expect to have any transaction open anymore. When this situation happens the worker has a delayed node that has no more items to run, since the task calling btrfs_run_delayed_items(), which is doing a transaction commit, picks the same node and runs all its items first. We can not wait for the worker to complete when running delayed items through btrfs_run_delayed_items(), because we call that function in several phases of a transaction commit, and that could cause a deadlock because the worker calls btrfs_join_transaction() and the task doing the transaction commit may have already set the transaction state to TRANS_STATE_COMMIT_DOING. Also it's not possible to get into a situation where only some of the items of a delayed node are added to the fs/subvolume tree in the current transaction and the remaining ones in the next transaction, because when running the items of a delayed inode we lock its mutex, effectively waiting for the worker if the worker is running the items of the delayed node already. Since this can only cause issues when unmounting a filesystem, fix it in a simple way by waiting for any jobs on the delayed workers queue before calling btrfs_commit_supper() at close_ctree(). This works because at this point no one can call btrfs_btree_balance_dirty() or btrfs_balance_delayed_items(), and if we end up waiting for any worker to complete, btrfs_commit_super() will commit the transaction created by the worker. CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Filipe Manana <fdmanana@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2020-02-28 13:04:36 +00:00
void btrfs_flush_workqueue(struct btrfs_workqueue *wq);
#endif