Re: [PATCH 4.4 25/26] blk: Ensure users for current->bio_list can see the full list.

[Ben Hutchings <ben.hutchings@codethink.co.uk>]

On Thu, 2017-04-06 at 10:38 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: NeilBrown <neilb@suse.com>
> 
> commit f5fe1b51905df7cfe4fdfd85c5fb7bc5b71a094f upstream.
> 
> Commit 79bd99596b73 ("blk: improve order of bio handling in generic_make_request()")
> changed current->bio_list so that it did not contain *all* of the
> queued bios, but only those submitted by the currently running
> make_request_fn.
> 
> There are two places which walk the list and requeue selected bios,
> and others that check if the list is empty.  These are no longer
> correct.
> 
> So redefine current->bio_list to point to an array of two lists, which
> contain all queued bios, and adjust various code to test or walk both
> lists.
> 
> Signed-off-by: NeilBrown <neilb@suse.com>
> Fixes: 79bd99596b73 ("blk: improve order of bio handling in generic_make_request()")
> Signed-off-by: Jens Axboe <axboe@fb.com>
> [jwang: backport to 4.4]
> Signed-off-by: Jack Wang <jinpu.wang@profitbricks.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  block/bio.c         |   12 +++++++++---
>  block/blk-core.c    |   31 +++++++++++++++++++------------
>  drivers/md/raid1.c  |    3 ++-
>  drivers/md/raid10.c |    3 ++-
>  4 files changed, 32 insertions(+), 17 deletions(-)

Why did you drop the changes in drivers/md/dm.c?

Ben.

> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -373,10 +373,14 @@ static void punt_bios_to_rescuer(struct
>  	bio_list_init(&punt);
>  	bio_list_init(&nopunt);
>  
> -	while ((bio = bio_list_pop(current->bio_list)))
> +	while ((bio = bio_list_pop(&current->bio_list[0])))
>  		bio_list_add(bio->bi_pool == bs ? &punt : &nopunt, bio);
> +	current->bio_list[0] = nopunt;
>  
> -	*current->bio_list = nopunt;
> +	bio_list_init(&nopunt);
> +	while ((bio = bio_list_pop(&current->bio_list[1])))
> +		bio_list_add(bio->bi_pool == bs ? &punt : &nopunt, bio);
> +	current->bio_list[1] = nopunt;
>  
>  	spin_lock(&bs->rescue_lock);
>  	bio_list_merge(&bs->rescue_list, &punt);
> @@ -464,7 +468,9 @@ struct bio *bio_alloc_bioset(gfp_t gfp_m
>  		 * we retry with the original gfp_flags.
>  		 */
>  
> -		if (current->bio_list && !bio_list_empty(current->bio_list))
> +		if (current->bio_list &&
> +		    (!bio_list_empty(&current->bio_list[0]) ||
> +		     !bio_list_empty(&current->bio_list[1])))
>  			gfp_mask &= ~__GFP_DIRECT_RECLAIM;
>  
>  		p = mempool_alloc(bs->bio_pool, gfp_mask);
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -2021,7 +2021,14 @@ end_io:
>   */
>  blk_qc_t generic_make_request(struct bio *bio)
>  {
> -	struct bio_list bio_list_on_stack;
> +	/*
> +	 * bio_list_on_stack[0] contains bios submitted by the current
> +	 * make_request_fn.
> +	 * bio_list_on_stack[1] contains bios that were submitted before
> +	 * the current make_request_fn, but that haven't been processed
> +	 * yet.
> +	 */
> +	struct bio_list bio_list_on_stack[2];
>  	blk_qc_t ret = BLK_QC_T_NONE;
>  
>  	if (!generic_make_request_checks(bio))
> @@ -2038,7 +2045,7 @@ blk_qc_t generic_make_request(struct bio
>  	 * should be added at the tail
>  	 */
>  	if (current->bio_list) {
> -		bio_list_add(current->bio_list, bio);
> +		bio_list_add(&current->bio_list[0], bio);
>  		goto out;
>  	}
>  
> @@ -2057,17 +2064,17 @@ blk_qc_t generic_make_request(struct bio
>  	 * bio_list, and call into ->make_request() again.
>  	 */
>  	BUG_ON(bio->bi_next);
> -	bio_list_init(&bio_list_on_stack);
> -	current->bio_list = &bio_list_on_stack;
> +	bio_list_init(&bio_list_on_stack[0]);
> +	current->bio_list = bio_list_on_stack;
>  	do {
>  		struct request_queue *q = bdev_get_queue(bio->bi_bdev);
>  
>  		if (likely(blk_queue_enter(q, __GFP_DIRECT_RECLAIM) == 0)) {
> -			struct bio_list lower, same, hold;
> +			struct bio_list lower, same;
>  
>  			/* Create a fresh bio_list for all subordinate requests */
> -			hold = bio_list_on_stack;
> -			bio_list_init(&bio_list_on_stack);
> +			bio_list_on_stack[1] = bio_list_on_stack[0];
> +			bio_list_init(&bio_list_on_stack[0]);
>  
>  			ret = q->make_request_fn(q, bio);
>  
> @@ -2077,19 +2084,19 @@ blk_qc_t generic_make_request(struct bio
>  			 */
>  			bio_list_init(&lower);
>  			bio_list_init(&same);
> -			while ((bio = bio_list_pop(&bio_list_on_stack)) != NULL)
> +			while ((bio = bio_list_pop(&bio_list_on_stack[0])) != NULL)
>  				if (q == bdev_get_queue(bio->bi_bdev))
>  					bio_list_add(&same, bio);
>  				else
>  					bio_list_add(&lower, bio);
>  			/* now assemble so we handle the lowest level first */
> -			bio_list_merge(&bio_list_on_stack, &lower);
> -			bio_list_merge(&bio_list_on_stack, &same);
> -			bio_list_merge(&bio_list_on_stack, &hold);
> +			bio_list_merge(&bio_list_on_stack[0], &lower);
> +			bio_list_merge(&bio_list_on_stack[0], &same);
> +			bio_list_merge(&bio_list_on_stack[0], &bio_list_on_stack[1]);
>  		} else {
>  			bio_io_error(bio);
>  		}
> -		bio = bio_list_pop(current->bio_list);
> +		bio = bio_list_pop(&bio_list_on_stack[0]);
>  	} while (bio);
>  	current->bio_list = NULL; /* deactivate */
>  
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -877,7 +877,8 @@ static sector_t wait_barrier(struct r1co
>  				     ((conf->start_next_window <
>  				       conf->next_resync + RESYNC_SECTORS) &&
>  				      current->bio_list &&
> -				      !bio_list_empty(current->bio_list))),
> +				     (!bio_list_empty(&current->bio_list[0]) ||
> +				      !bio_list_empty(&current->bio_list[1])))),
>  				    conf->resync_lock);
>  		conf->nr_waiting--;
>  	}
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -946,7 +946,8 @@ static void wait_barrier(struct r10conf
>  				    !conf->barrier ||
>  				    (conf->nr_pending &&
>  				     current->bio_list &&
> -				     !bio_list_empty(current->bio_list)),
> +				     (!bio_list_empty(&current->bio_list[0]) ||
> +				      !bio_list_empty(&current->bio_list[1]))),
>  				    conf->resync_lock);
>  		conf->nr_waiting--;
>  	}
> 
> 
> 

-- 
Ben Hutchings
Software Developer, Codethink Ltd.