The current implementation of the reclaim lockup detection can lead to
false positives and those even happen and usually lead to tweak the code
to silence the lockdep by using GFP_NOFS even though the context can use
__GFP_FS just fine.
See
http://lkml.kernel.org/r/20160512080321.GA18496@dastard
as an example.
=================================
[ INFO: inconsistent lock state ]
4.5.0-rc2+ #4 Tainted: G O
---------------------------------
inconsistent {RECLAIM_FS-ON-R} -> {IN-RECLAIM_FS-W} usage.
kswapd0/543 [HC0[0]:SC0[0]:HE1:SE1] takes:
(&xfs_nondir_ilock_class){++++-+}, at: xfs_ilock+0x177/0x200 [xfs]
{RECLAIM_FS-ON-R} state was registered at:
mark_held_locks+0x79/0xa0
lockdep_trace_alloc+0xb3/0x100
kmem_cache_alloc+0x33/0x230
kmem_zone_alloc+0x81/0x120 [xfs]
xfs_refcountbt_init_cursor+0x3e/0xa0 [xfs]
__xfs_refcount_find_shared+0x75/0x580 [xfs]
xfs_refcount_find_shared+0x84/0xb0 [xfs]
xfs_getbmap+0x608/0x8c0 [xfs]
xfs_vn_fiemap+0xab/0xc0 [xfs]
do_vfs_ioctl+0x498/0x670
SyS_ioctl+0x79/0x90
entry_SYSCALL_64_fastpath+0x12/0x6f
CPU0
----
lock(&xfs_nondir_ilock_class);
<Interrupt>
lock(&xfs_nondir_ilock_class);
*** DEADLOCK ***
3 locks held by kswapd0/543:
stack backtrace:
CPU: 0 PID: 543 Comm: kswapd0 Tainted: G O 4.5.0-rc2+ #4
Call Trace:
lock_acquire+0xd8/0x1e0
down_write_nested+0x5e/0xc0
xfs_ilock+0x177/0x200 [xfs]
xfs_reflink_cancel_cow_range+0x150/0x300 [xfs]
xfs_fs_evict_inode+0xdc/0x1e0 [xfs]
evict+0xc5/0x190
dispose_list+0x39/0x60
prune_icache_sb+0x4b/0x60
super_cache_scan+0x14f/0x1a0
shrink_slab.part.63.constprop.79+0x1e9/0x4e0
shrink_zone+0x15e/0x170
kswapd+0x4f1/0xa80
kthread+0xf2/0x110
ret_from_fork+0x3f/0x70
To quote Dave:
"Ignoring whether reflink should be doing anything or not, that's a
"xfs_refcountbt_init_cursor() gets called both outside and inside
transactions" lockdep false positive case. The problem here is lockdep
has seen this allocation from within a transaction, hence a GFP_NOFS
allocation, and now it's seeing it in a GFP_KERNEL context. Also note
that we have an active reference to this inode.
So, because the reclaim annotations overload the interrupt level
detections and it's seen the inode ilock been taken in reclaim
("interrupt") context, this triggers a reclaim context warning where
it thinks it is unsafe to do this allocation in GFP_KERNEL context
holding the inode ilock..."
This sounds like a fundamental problem of the reclaim lock detection.
It is really impossible to annotate such a special usecase IMHO unless
the reclaim lockup detection is reworked completely. Until then it is
much better to provide a way to add "I know what I am doing flag" and
mark problematic places. This would prevent from abusing GFP_NOFS flag
which has a runtime effect even on configurations which have lockdep
disabled.
Introduce __GFP_NOLOCKDEP flag which tells the lockdep gfp tracking to
skip the current allocation request.
While we are at it also make sure that the radix tree doesn't
accidentaly override tags stored in the upper part of the gfp_mask.
Link: http://lkml.kernel.org/r/20170306131408.9828-3-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Chris Mason <clm@fb.com>
Cc: David Sterba <dsterba@suse.cz>
Cc: Jan Kara <jack@suse.cz>
Cc: Brian Foster <bfoster@redhat.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
7e7844226f