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With the following two conditions, bio will be lost:
1) blk plug is not enabled, for example, __blkdev_direct_IO_simple() and
__blkdev_direct_IO_async();
2) bio plug is enabled, for example write IO for raid1/raid10 while
bitmap is enabled;
Root cause is that blk_finish_plug() will add the bio to
curent->bio_list, while such bio will not be handled:
__submit_bio_noacct
current->bio_list = bio_list_on_stack;
blk_start_plug
do {
dm_submit_bio
md_handle_request
raid10_write_request
-> generate new bio for underlying disks
raid1_add_bio_to_plug -> bio is added to plug
} while ((bio = bio_list_pop(&bio_list_on_stack[0])))
-> previous bio are all handled
blk_finish_plug
raid10_unplug
raid1_submit_write
submit_bio_noacct
if (current->bio_list)
bio_list_add(¤t->bio_list[0], bio)
-> add new bio
current->bio_list = NULL
-> new bio is lost
Fix the problem by moving the plug into the while loop, so that
current->bio_list will still be handled after blk_finish_plug().
By the way, enable plug for raid1/raid10 in this case will also prevent
delay IO handling into daemon thread, which should also improve IO
performance.
Fixes: 060406c61c ("block: add plug while submitting IO")
Reported-by: Changhui Zhong <czhong@redhat.com>
Closes: https://lore.kernel.org/all/CAGVVp+Xsmzy2G9YuEatfMT6qv1M--YdOCQ0g7z7OVmcTbBxQAg@mail.gmail.com/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Tested-by: Changhui Zhong <czhong@redhat.com>
Link: https://lore.kernel.org/r/20240521200308.983986-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
9a42891c35