linux-kernel - [PATCH 4.19 34/84] btrfs: simplify inode locking for RWF

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Date:   Fri, 17 Jan 2020 00:18:08 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Goldwyn Rodrigues <rgoldwyn@...e.com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 4.19 34/84] btrfs: simplify inode locking for RWF_NOWAIT

From: Goldwyn Rodrigues <rgoldwyn@...e.com>

commit 9cf35f673583ccc9f3e2507498b3079d56614ad3 upstream.

This is similar to 942491c9e6d6 ("xfs: fix AIM7 regression"). Apparently
our current rwsem code doesn't like doing the trylock, then lock for
real scheme. This causes extra contention on the lock and can be
measured eg. by AIM7 benchmark.  So change our read/write methods to
just do the trylock for the RWF_NOWAIT case.

Fixes: edf064e7c6fe ("btrfs: nowait aio support")
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@...e.com>
Reviewed-by: David Sterba <dsterba@...e.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/file.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1903,9 +1903,10 @@ static ssize_t btrfs_file_write_iter(str
 	    (iocb->ki_flags & IOCB_NOWAIT))
 		return -EOPNOTSUPP;
 
-	if (!inode_trylock(inode)) {
-		if (iocb->ki_flags & IOCB_NOWAIT)
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (!inode_trylock(inode))
 			return -EAGAIN;
+	} else {
 		inode_lock(inode);
 	}