On Tue, May 26, 2020 at 09:34:57AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
>
> 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@xxxxxxxxx>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> Tested-by: Dave Airlie <airlied@xxxxxxxxx>
> ---
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> 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 fc87ea9f6843..34cbcfde9228 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 f3d18a1f5b20..2f7e89e4be3e 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -488,7 +488,7 @@ 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;
> }
>
