From: Omar Sandoval <osandov@fb.com>
Date: Thu, 15 Aug 2019 14:04:02 -0700
Git-commit: c09767a8960ca0500fb636bf73686723337debf4
Patch-mainline: 5.4
References: bsc#1174438
Subject: [PATCH] btrfs: use correct count in btrfs_file_write_iter()
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: Filipe Manana <fdmanana@suse.com>
---
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 5711d6851b63..684fd1d4680a 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1884,7 +1884,7 @@ 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;
@@ -1902,6 +1902,7 @@ 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,
--
2.26.2