[1/5] Btrfs: use correct count in btrfs_file_write_iter()
diff mbox series

Message ID 06b24b06988a5fac5881a0eef613aa2ef0c63834.1565900769.git.osandov@fb.com
State New
Headers show
Series
  • Btrfs: add interface for writing compressed extent directly
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Commit Message

Omar Sandoval Aug. 15, 2019, 9:04 p.m. UTC
From: Omar Sandoval <osandov@fb.com>

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")
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/btrfs/file.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Josef Bacik Aug. 16, 2019, 4:56 p.m. UTC | #1
On Thu, Aug 15, 2019 at 02:04:02PM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> 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")
> Signed-off-by: Omar Sandoval <osandov@fb.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

Patch
diff mbox series

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index b31991f0f440..4393b6b24e02 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1885,7 +1885,7 @@  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;
 
@@ -1906,6 +1906,7 @@  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,