From 9cf35f673583ccc9f3e2507498b3079d56614ad3 Mon Sep 17 00:00:00 2001
From: Goldwyn Rodrigues <rgoldwyn@suse.com>
Date: Wed Sep 11 11:45:15 2019 -0500
Subject: [PATCH] btrfs: simplify inode locking for RWF_NOWAIT 
Git-commit: 9cf35f673583ccc9f3e2507498b3079d56614ad3
References: git-fixes
Patch-mainline: v5.5-rc1

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@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

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

--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1899,9 +1899,10 @@
 	loff_t oldsize;
 	int clean_page = 0;
 
-	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);
 	}