On Fri, Jul 29, 2022 at 02:52:43PM +0800, Zhang Wensheng wrote:
From: Zhang Wensheng zhangwensheng5@huawei.com
In the use of q_usage_counter of request_queue, blk_cleanup_queue using "wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter))" to wait q_usage_counter becoming zero. however, if the q_usage_counter becoming zero quickly, and percpu_ref_exit will execute and ref->data will be freed, maybe another process will cause a null-defef problem like below:
CPU0 CPU1 blk_cleanup_queue blk_freeze_queue blk_mq_freeze_queue_wait scsi_end_request percpu_ref_get ... percpu_ref_put atomic_long_sub_and_test percpu_ref_exit ref->data -> NULL ref->data->release(ref) -> null-deref
Fix it by setting flag(QUEUE_FLAG_USAGE_COUNT_SYNC) to add synchronization mechanism, when ref->data->release is called, the flag will be setted, and the "wait_event" in blk_mq_freeze_queue_wait must wait flag becoming true as well, which will limit percpu_ref_exit to execute ahead of time.
Signed-off-by: Zhang Wensheng zhangwensheng5@huawei.com
block/blk-core.c | 4 +++- block/blk-mq.c | 7 +++++++ include/linux/blk-mq.h | 1 + include/linux/blkdev.h | 2 ++ 4 files changed, 13 insertions(+), 1 deletion(-)
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This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly.
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