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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Omar Sandoval <osandov@fb.com>,
	Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>, Sasha Levin <sashal@kernel.org>,
	linux-btrfs@vger.kernel.org
Subject: [PATCH AUTOSEL 4.14 294/371] btrfs: use correct count in btrfs_file_write_iter()
Date: Thu, 16 Jan 2020 12:22:46 -0500
Message-ID: <20200116172403.18149-237-sashal@kernel.org> (raw)
In-Reply-To: <20200116172403.18149-1-sashal@kernel.org>

From: Omar Sandoval <osandov@fb.com>

[ Upstream commit c09767a8960ca0500fb636bf73686723337debf4 ]

generic_write_checks() may modify iov_iter_count(), so we must get the
count after the call, not before. Using the wrong one has a couple of
consequences:

1. We check a longer range in check_can_nocow() for nowait than we're
   actually writing.
2. We create extra hole extent maps in btrfs_cont_expand(). As far as I
   can tell, this is harmless, but I might be missing something.

These issues are pretty minor, but let's fix it before something more
important trips on it.

Fixes: edf064e7c6fe ("btrfs: nowait aio support")
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/btrfs/file.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index bf654d48eb46..dd5f6e0df63f 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1882,7 +1882,7 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
 	bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
 	ssize_t err;
 	loff_t pos;
-	size_t count = iov_iter_count(from);
+	size_t count;
 	loff_t oldsize;
 	int clean_page = 0;
 
@@ -1903,6 +1903,7 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
 	}
 
 	pos = iocb->ki_pos;
+	count = iov_iter_count(from);
 	if (iocb->ki_flags & IOCB_NOWAIT) {
 		/*
 		 * We will allocate space in case nodatacow is not set,
-- 
2.20.1


      parent reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200116172403.18149-1-sashal@kernel.org>
2020-01-16 17:22 ` [PATCH AUTOSEL 4.14 291/371] Btrfs: fix hang when loading existing inode cache off disk Sasha Levin
2020-01-16 17:22 ` [PATCH AUTOSEL 4.14 292/371] Btrfs: fix inode cache waiters hanging on failure to start caching thread Sasha Levin
2020-01-16 17:22 ` [PATCH AUTOSEL 4.14 293/371] Btrfs: fix inode cache waiters hanging on path allocation failure Sasha Levin
2020-01-16 17:22 ` Sasha Levin [this message]

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