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

From: Ben Hutchings
Date: Thu Apr 06 2017 - 14:18:21 EST

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@xxxxxxxx>
>
> 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@xxxxxxxx>
> Fixes: 79bd99596b73 ("blk: improve order of bio handling in generic_make_request()")
> Signed-off-by: Jens Axboe <axboe@xxxxxx>
> [jwang: backport to 4.4]
> Signed-off-by: Jack Wang <jinpu.wang@xxxxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> 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.