Re: [BUG] MD/RAID1 hung forever on freeze_array

On Mon, Dec 19, 2016 at 12:16 PM, Jinpu Wang
[off-list ref] wrote:

Hi Neil,

After apply the patch below, it paniced during boot in
generic_make_request-> bio_list_pop.
Looks related to you do bio_list_init(&bio_list_on_stack); again.

quoted

diff --git a/block/blk-core.c b/block/blk-core.c
index 14d7c0740dc0..3436b6fc3ef8 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c

@@ -2036,10 +2036,31 @@ blk_qc_t generic_make_request(struct bio *bio)
                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 */
+                       bio_list_merge(&hold, &bio_list_on_stack);
+                       bio_list_init(&bio_list_on_stack); ??? maybe init hold, and then merge bio_list_on_stack?
                        ret = q->make_request_fn(q, bio);

                        blk_queue_exit(q);

+                       /* sort new bios into those for a lower level
+                        * and those for the same level
+                        */
+                       bio_list_init(&lower);
+                       bio_list_init(&same);
+                       while ((bio = bio_list_pop(&bio_list_on_stack)) != 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 = bio_list_pop(current->bio_list);
                } else {
                        struct bio *bio_next = bio_list_pop(current->bio_list);

Seems we don't need bio_list hold at all, lower and seem merge back to
bio_list_on_stack?
I'm currently testing patch below, so far so good.

diff --git a/block/blk-core.c b/block/blk-core.c
index e8d15d8..9c56cf7 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c

@@ -2064,10 +2064,24 @@ blk_qc_t generic_make_request(struct bio *bio)
                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;

                        ret = q->make_request_fn(q, bio);

                        blk_queue_exit(q);
+                       /* sort new bios into those for a lower level
+                        * and those for the same level
+                        */
+                       bio_list_init(&lower);
+                       bio_list_init(&same);
+                       while ((bio = bio_list_pop(&bio_list_on_stack)) != 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 = bio_list_pop(current->bio_list);
                } else {

-- 
Jinpu Wang
Linux Kernel Developer

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