From: Filipe Manana fdmanana@suse.com
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 --- fs/btrfs/inode.c | 3 --- 1 file changed, 3 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 18111b0263d71..6aa200e373c8f 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -8262,9 +8262,6 @@ 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);