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SubjectRe: lockdep trace with xfs + mm in it from 5.7.0-rc5
OTOH, it didn't take that long to whip up a patch.

Dave, does this fix your problem?

--D
---
xfs: more lockdep whackamole with kmem_alloc*

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>
---
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 224462b8bf08..55e184722b81 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;
}
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