Re: [PATCH] fs: block pipe_write() on a frozen filesystem

[Jan Kara <jack@suse.cz>]

On Thu 27-09-12 10:47:59, Eric Sandeen wrote:
> I noticed that this can sneak past a frozen filesystem:
> 
> # mkfifo /mnt/test/fifo
> # echo foo > /mnt/test/fifo &
> # fsfreeze -f /mnt/test
> # cat /mnt/test/fifo
> 
> and we get a warning that jbd2 has entered a transaction while frozen:
> 
> WARNING: at fs/ext4/super.c:240 ext4_journal_start_sb+0xce/0xe0 [ext4]() (Not tainted)
> 
> which is: WARN_ON(sb->s_writers.frozen == SB_FREEZE_COMPLETE);
> 
> and we get there via the file_update_time() path in pipe_write().
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> Is this too big a hammer?  file_update_time() is conditional...
  I think your patch is fine. Just skipping update of mtime could cause
userspace issues (although they seem rather unlikely to me). So you can add
  Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 8d85d70..d19a709 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -501,6 +501,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
>  
>  	do_wakeup = 0;
>  	ret = 0;
> +	sb_start_write(inode->i_sb);
>  	mutex_lock(&inode->i_mutex);
>  	pipe = inode->i_pipe;
>  
> @@ -659,6 +660,7 @@ out:
>  		if (err)
>  			ret = err;
>  	}
> +	sb_end_write(inode->i_sb);
>  	return ret;
>  }
>  
>