btrfs: fix failure of RWF_NOWAIT write into prealloc extent beyond eof

commit 4b1946284dd6641afdb9457101056d9e6ee6204c upstream.

If we attempt to write to prealloc extent located after eof using a
RWF_NOWAIT write, we always fail with -EAGAIN.

We do actually check if we have an allocated extent for the write at
the start of btrfs_file_write_iter() through a call to check_can_nocow(),
but later when we go into the actual direct IO write path we simply
return -EAGAIN if the write starts at or beyond EOF.

Trivial to reproduce:

  $ mkfs.btrfs -f /dev/sdb
  $ mount /dev/sdb /mnt

  $ touch /mnt/foo
  $ chattr +C /mnt/foo

  $ xfs_io -d -c "pwrite -S 0xab 0 64K" /mnt/foo
  wrote 65536/65536 bytes at offset 0
  64 KiB, 16 ops; 0.0004 sec (135.575 MiB/sec and 34707.1584 ops/sec)

  $ xfs_io -c "falloc -k 64K 1M" /mnt/foo

  $ xfs_io -d -c "pwrite -N -V 1 -S 0xfe -b 64K 64K 64K" /mnt/foo
  pwrite: Resource temporarily unavailable

On xfs and ext4 the write succeeds, as expected.

Fix this by removing the wrong check at btrfs_direct_IO().

Fixes: edf064e7c6fec3 ("btrfs: nowait aio support")
CC: stable@vger.kernel.org # 4.14+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit a79c3a99ac8187d79ce7cc6be8329454d2321ef5)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e0712cba70af1aaed33fd137bb5f3a8f748c9905..b37a72b765e98cd013794a0435fcedf5710dea7e 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8214,9 +8214,6 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
                        dio_data.overwrite = 1;
                        inode_unlock(inode);
                        relock = true;
-               } else if (iocb->ki_flags & IOCB_NOWAIT) {
-                       ret = -EAGAIN;
-                       goto out;
                }
                ret = btrfs_delalloc_reserve_space(inode, &data_reserved,
                                                   offset, count);