Commit c09767a8 authored Aug 15, 2019 by Omar Sandoval Committed by David Sterba Sep 09, 2019

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: edf064e7 ("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>

parent c82f823c

fs/btrfs/file.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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,

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