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btrfs: use correct count in btrfs_file_write_iter()

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[ 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>
This commit is contained in:
Omar Sandoval 2019-08-15 14:04:02 -07:00 committed by Greg Kroah-Hartman
parent 510cd98350
commit a7a67b4e8e
1 changed files with 2 additions and 1 deletions
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3
fs/btrfs/file.c
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@ -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;
@ -1904,6 +1904,7 @@ 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,