blk: Ensure users for current->bio_list can see the full list.

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>

4 files changed, 45 insertions, 29 deletions

diff --git a/block/bio.c b/block/bio.c
index 5eec5e08417f..e75878f8b14a 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -376,10 +376,14 @@ static void punt_bios_to_rescuer(struct bio_set *bs)
         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);
@@ -466,7 +470,9 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
                  * 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);
diff --git a/block/blk-core.c b/block/blk-core.c
index 0eeb99ef654f..d772c221cc17 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1973,7 +1973,14 @@ 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))
@@ -1990,7 +1997,7 @@ blk_qc_t generic_make_request(struct bio *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;
         }
 
@@ -2009,18 +2016,17 @@ blk_qc_t generic_make_request(struct bio *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, false) == 0)) {
-                        struct bio_list 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);
 
                         blk_queue_exit(q);
@@ -2030,19 +2036,19 @@ blk_qc_t generic_make_request(struct bio *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 */
 
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index f4ffd1eb8f44..dfb75979e455 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -989,26 +989,29 @@ static void flush_current_bio_list(struct blk_plug_cb *cb, bool from_schedule)
         struct dm_offload *o = container_of(cb, struct dm_offload, cb);
         struct bio_list list;
         struct bio *bio;
+        int i;
 
         INIT_LIST_HEAD(&o->cb.list);
 
         if (unlikely(!current->bio_list))
                 return;
 
-        list = *current->bio_list;
-        bio_list_init(current->bio_list);
-
-        while ((bio = bio_list_pop(&list))) {
-                struct bio_set *bs = bio->bi_pool;
-                if (unlikely(!bs) || bs == fs_bio_set) {
-                        bio_list_add(current->bio_list, bio);
-                        continue;
+        for (i = 0; i < 2; i++) {
+                list = current->bio_list[i];
+                bio_list_init(&current->bio_list[i]);
+
+                while ((bio = bio_list_pop(&list))) {
+                        struct bio_set *bs = bio->bi_pool;
+                        if (unlikely(!bs) || bs == fs_bio_set) {
+                                bio_list_add(&current->bio_list[i], bio);
+                                continue;
+                        }
+
+                        spin_lock(&bs->rescue_lock);
+                        bio_list_add(&bs->rescue_list, bio);
+                        queue_work(bs->rescue_workqueue, &bs->rescue_work);
+                        spin_unlock(&bs->rescue_lock);
                 }
-
-                spin_lock(&bs->rescue_lock);
-                bio_list_add(&bs->rescue_list, bio);
-                queue_work(bs->rescue_workqueue, &bs->rescue_work);
-                spin_unlock(&bs->rescue_lock);
         }
 }
 
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 063c43d83b72..0536658c9d40 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -974,7 +974,8 @@ static void wait_barrier(struct r10conf *conf)
                                     !conf->barrier ||
                                     (atomic_read(&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--;
                 if (!conf->nr_waiting)