From: "Darrick J. Wong" darrick.wong@oracle.com
[ Upstream commit 6dcde60efd946e38fac8d276a6ca47492103e856 ]
Dave Airlie reported the following lockdep complaint:
====================================================== WARNING: possible circular locking dependency detected 5.7.0-0.rc5.20200515git1ae7efb38854.1.fc33.x86_64 #1 Not tainted
kswapd0/159 is trying to acquire lock: ffff9b38d01a4470 (&xfs_nondir_ilock_class){++++}-{3:3}, at: xfs_ilock+0xde/0x2c0 [xfs]
but task is already holding lock: ffffffffbbb8bd00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (fs_reclaim){+.+.}-{0:0}: fs_reclaim_acquire+0x34/0x40 __kmalloc+0x4f/0x270 kmem_alloc+0x93/0x1d0 [xfs] kmem_alloc_large+0x4c/0x130 [xfs] xfs_attr_copy_value+0x74/0xa0 [xfs] xfs_attr_get+0x9d/0xc0 [xfs] xfs_get_acl+0xb6/0x200 [xfs] get_acl+0x81/0x160 posix_acl_xattr_get+0x3f/0xd0 vfs_getxattr+0x148/0x170 getxattr+0xa7/0x240 path_getxattr+0x52/0x80 do_syscall_64+0x5c/0xa0 entry_SYSCALL_64_after_hwframe+0x49/0xb3
-> #0 (&xfs_nondir_ilock_class){++++}-{3:3}: __lock_acquire+0x1257/0x20d0 lock_acquire+0xb0/0x310 down_write_nested+0x49/0x120 xfs_ilock+0xde/0x2c0 [xfs] xfs_reclaim_inode+0x3f/0x400 [xfs] xfs_reclaim_inodes_ag+0x20b/0x410 [xfs] xfs_reclaim_inodes_nr+0x31/0x40 [xfs] super_cache_scan+0x190/0x1e0 do_shrink_slab+0x184/0x420 shrink_slab+0x182/0x290 shrink_node+0x174/0x680 balance_pgdat+0x2d0/0x5f0 kswapd+0x21f/0x510 kthread+0x131/0x150 ret_from_fork+0x3a/0x50
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1 ---- ----lock(fs_reclaim); lock(&xfs_nondir_ilock_class); lock(fs_reclaim); lock(&xfs_nondir_ilock_class);
*** DEADLOCK ***
4 locks held by kswapd0/159: #0: ffffffffbbb8bd00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30 #1: ffffffffbbb7cef8 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x115/0x290 #2: ffff9b39f07a50e8 (&type->s_umount_key#56){++++}-{3:3}, at: super_cache_scan+0x38/0x1e0 #3: ffff9b39f077f258 (&pag->pag_ici_reclaim_lock){+.+.}-{3:3}, at: xfs_reclaim_inodes_ag+0x82/0x410 [xfs]
This is a known false positive because inodes cannot simultaneously be getting reclaimed and the target of a getxattr operation, but lockdep doesn't know that. We can (selectively) shut up lockdep until either it gets smarter or we change inode reclaim not to require the ILOCK by applying a stupid GFP_NOLOCKDEP bandaid.
Reported-by: Dave Airlie airlied@gmail.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Tested-by: Dave Airlie airlied@gmail.com Reviewed-by: Brian Foster bfoster@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/xfs/kmem.h | 6 +++++- fs/xfs/libxfs/xfs_attr_leaf.c | 2 +- 2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h index 6143117770e9..11623489b769 100644 --- a/fs/xfs/kmem.h +++ b/fs/xfs/kmem.h @@ -19,6 +19,7 @@ typedef unsigned __bitwise xfs_km_flags_t; #define KM_NOFS ((__force xfs_km_flags_t)0x0004u) #define KM_MAYFAIL ((__force xfs_km_flags_t)0x0008u) #define KM_ZERO ((__force xfs_km_flags_t)0x0010u) +#define KM_NOLOCKDEP ((__force xfs_km_flags_t)0x0020u)
/* * We use a special process flag to avoid recursive callbacks into @@ -30,7 +31,7 @@ kmem_flags_convert(xfs_km_flags_t flags) { gfp_t lflags;
- BUG_ON(flags & ~(KM_NOFS|KM_MAYFAIL|KM_ZERO)); + BUG_ON(flags & ~(KM_NOFS | KM_MAYFAIL | KM_ZERO | KM_NOLOCKDEP));
lflags = GFP_KERNEL | __GFP_NOWARN; if (flags & KM_NOFS) @@ -49,6 +50,9 @@ kmem_flags_convert(xfs_km_flags_t flags) if (flags & KM_ZERO) lflags |= __GFP_ZERO;
+ if (flags & KM_NOLOCKDEP) + lflags |= __GFP_NOLOCKDEP; + return lflags; }
diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c index 863444e2dda7..1d67cc9f4209 100644 --- a/fs/xfs/libxfs/xfs_attr_leaf.c +++ b/fs/xfs/libxfs/xfs_attr_leaf.c @@ -489,7 +489,7 @@ xfs_attr_copy_value( }
if (!args->value) { - args->value = kmem_alloc_large(valuelen, 0); + args->value = kmem_alloc_large(valuelen, KM_NOLOCKDEP); if (!args->value) return -ENOMEM; }