Re: [PATCH] Btrfs: fix error path when failing to submit bio for direct IO write

[Liu Bo <bo.li.liu@oracle.com>]

On Tue, Nov 24, 2015 at 05:25:18PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> Commit 61de718fceb6 ("Btrfs: fix memory corruption on failure to submit
> bio for direct IO") fixed problems with the error handling code after we
> fail to submit a bio for direct IO. However there were 2 problems that it
> did not address when the failure is due to memory allocation failures for
> direct IO writes:
> 
> 1) We considered that there could be only one ordered extent for the whole
>    IO range, which is not always true, as we can have multiple;
> 
> 2) It did not set the bit BTRFS_ORDERED_IO_DONE in the ordered extent,
>    which can make other tasks running btrfs_wait_logged_extents() hang
>    forever, since they wait for that bit to be set. The general assumption
>    is that regardless of an error, the BTRFS_ORDERED_IO_DONE is always set
>    and it precedes setting the bit BTRFS_ORDERED_COMPLETE.
> 
> Fix these issues by moving part of the btrfs_endio_direct_write() handler
> into a new helper function and having that new helper function called when
> we fail to allocate memory to submit the bio (and its private object) for
> a direct IO write.
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>  fs/btrfs/inode.c | 54 +++++++++++++++++++++++++++---------------------------
>  1 file changed, 27 insertions(+), 27 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index f82d1f4..4f8560c 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -7995,22 +7995,22 @@ static void btrfs_endio_direct_read(struct bio *bio)
>  	bio_put(bio);
>  }
>  
> -static void btrfs_endio_direct_write(struct bio *bio)
> +static void btrfs_endio_direct_write_update_ordered(struct inode *inode,
> +						    const u64 offset,
> +						    const u64 bytes,
> +						    const int uptodate)
>  {
> -	struct btrfs_dio_private *dip = bio->bi_private;
> -	struct inode *inode = dip->inode;
>  	struct btrfs_root *root = BTRFS_I(inode)->root;
>  	struct btrfs_ordered_extent *ordered = NULL;
> -	u64 ordered_offset = dip->logical_offset;
> -	u64 ordered_bytes = dip->bytes;
> -	struct bio *dio_bio;
> +	u64 ordered_offset = offset;
> +	u64 ordered_bytes = bytes;
>  	int ret;
>  
>  again:
>  	ret = btrfs_dec_test_first_ordered_pending(inode, &ordered,
>  						   &ordered_offset,
>  						   ordered_bytes,
> -						   !bio->bi_error);
> +						   uptodate);
>  	if (!ret)
>  		goto out_test;
>  
> @@ -8023,13 +8023,22 @@ out_test:
>  	 * our bio might span multiple ordered extents.  If we haven't
>  	 * completed the accounting for the whole dio, go back and try again
>  	 */
> -	if (ordered_offset < dip->logical_offset + dip->bytes) {
> -		ordered_bytes = dip->logical_offset + dip->bytes -
> -			ordered_offset;
> +	if (ordered_offset < offset + bytes) {
> +		ordered_bytes = offset + bytes - ordered_offset;
>  		ordered = NULL;
>  		goto again;
>  	}
> -	dio_bio = dip->dio_bio;
> +}
> +
> +static void btrfs_endio_direct_write(struct bio *bio)
> +{
> +	struct btrfs_dio_private *dip = bio->bi_private;
> +	struct bio *dio_bio = dip->dio_bio;
> +
> +	btrfs_endio_direct_write_update_ordered(dip->inode,
> +						dip->logical_offset,
> +						dip->bytes,
> +						!bio->bi_error);
>  
>  	kfree(dip);
>  
> @@ -8365,24 +8374,15 @@ free_ordered:
>  		dip = NULL;
>  		io_bio = NULL;
>  	} else {
> -		if (write) {
> -			struct btrfs_ordered_extent *ordered;
> -
> -			ordered = btrfs_lookup_ordered_extent(inode,
> -							      file_offset);
> -			set_bit(BTRFS_ORDERED_IOERR, &ordered->flags);
> -			/*
> -			 * Decrements our ref on the ordered extent and removes
> -			 * the ordered extent from the inode's ordered tree,
> -			 * doing all the proper resource cleanup such as for the
> -			 * reserved space and waking up any waiters for this
> -			 * ordered extent (through btrfs_remove_ordered_extent).
> -			 */
> -			btrfs_finish_ordered_io(ordered);
> -		} else {
> +		if (write)
> +			btrfs_endio_direct_write_update_ordered(inode,
> +						file_offset,
> +						dio_bio->bi_iter.bi_size,
> +						1);

uptodate=1 won't set IOERR for ordered extent, is that expected?

Thanks,

-liubo
> +		else
>  			unlock_extent(&BTRFS_I(inode)->io_tree, file_offset,
>  			      file_offset + dio_bio->bi_iter.bi_size - 1);
> -		}
> +
>  		dio_bio->bi_error = -EIO;
>  		/*
>  		 * Releases and cleans up our dio_bio, no need to bio_put()
> -- 
> 2.1.3
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html