xfs: use __GFP_NOLOCKDEP instead of GFP_NOFS

In the past we've had problems with lockdep false positives stemming
from inode locking occurring in memory reclaim contexts (e.g. from
superblock shrinkers). Lockdep doesn't know that inodes access from
above memory reclaim cannot be accessed from below memory reclaim
(and vice versa) but there has never been a good solution to solving
this problem with lockdep annotations.

This situation isn't unique to inode locks - buffers are also locked
above and below memory reclaim, and we have to maintain lock
ordering for them - and against inodes - appropriately. IOWs, the
same code paths and locks are taken both above and below memory
reclaim and so we always need to make sure the lock orders are
consistent. We are spared the lockdep problems this might cause
by the fact that semaphores and bit locks aren't covered by lockdep.

In general, this sort of lockdep false positive detection is cause
by code that runs GFP_KERNEL memory allocation with an actively
referenced inode locked. When it is run from a transaction, memory
allocation is automatically GFP_NOFS, so we don't have reclaim
recursion issues. So in the places where we do memory allocation
with inodes locked outside of a transaction, we have explicitly set
them to use GFP_NOFS allocations to prevent lockdep false positives
from being reported if the allocation dips into direct memory
reclaim.

More recently, __GFP_NOLOCKDEP was added to the memory allocation
flags to tell lockdep not to track that particular allocation for
the purposes of reclaim recursion detection. This is a much better
way of preventing false positives - it allows us to use GFP_KERNEL
context outside of transactions, and allows direct memory reclaim to
proceed normally without throwing out false positive deadlock
warnings.

The obvious places that lock inodes and do memory allocation are the
lookup paths and inode extent list initialisation. These occur in
non-transactional GFP_KERNEL contexts, and so can run direct reclaim
and lock inodes.

This patch makes a first path through all the explicit GFP_NOFS
allocations in XFS and converts the obvious ones to GFP_KERNEL |
__GFP_NOLOCKDEP as a first step towards removing explicit GFP_NOFS
allocations from the XFS code.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

1 files changed, 4 insertions, 10 deletions

diff --git a/fs/xfs/libxfs/xfs_dir2.c b/fs/xfs/libxfs/xfs_dir2.c
index e60aa8f8d0a7..728f72f0d078 100644
--- a/fs/xfs/libxfs/xfs_dir2.c
+++ b/fs/xfs/libxfs/xfs_dir2.c
@@ -333,7 +333,8 @@ xfs_dir_cilookup_result(
 					!(args->op_flags & XFS_DA_OP_CILOOKUP))
 		return -EEXIST;
 
-	args->value = kmalloc(len, GFP_NOFS | __GFP_RETRY_MAYFAIL);
+	args->value = kmalloc(len,
+			GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_RETRY_MAYFAIL);
 	if (!args->value)
 		return -ENOMEM;
 
@@ -364,15 +365,8 @@ xfs_dir_lookup(
 	ASSERT(S_ISDIR(VFS_I(dp)->i_mode));
 	XFS_STATS_INC(dp->i_mount, xs_dir_lookup);
 
-	/*
-	 * We need to use KM_NOFS here so that lockdep will not throw false
-	 * positive deadlock warnings on a non-transactional lookup path. It is
-	 * safe to recurse into inode recalim in that case, but lockdep can't
-	 * easily be taught about it. Hence KM_NOFS avoids having to add more
-	 * lockdep Doing this avoids having to add a bunch of lockdep class
-	 * annotations into the reclaim path for the ilock.
-	 */
-	args = kzalloc(sizeof(*args), GFP_NOFS | __GFP_NOFAIL);
+	args = kzalloc(sizeof(*args),
+			GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOFAIL);
 	args->geo = dp->i_mount->m_dir_geo;
 	args->name = name->name;
 	args->namelen = name->len;