[ufs]: [scsi]: BUG: spinlock recursion on CPU#4

[Asutosh Das (asd)]

Hi All,

Recently, I came across an issue with the below call stack.

-000|arch_counter_get_cntvct(inline)
-000|__delay()
-001|__const_udelay(?)
-002|msm_trigger_wdog_bite()
-003|spin_dump(inline)
-003|spin_bug(lock = ?, ?)
-004|current_thread_info(inline)
-004|debug_spin_lock_before(inline)
-004|do_raw_spin_lock()
-005|raw_spin_lock_irqsave(lock = ?)
-006|blk_end_bidi_request(inline)
-006|blk_end_request_all(rq = ?, error = 0) <-- this tries to acquire 
the lock acquired by blk_delay_work (-024) and spinbug recursion occurs

-007|dm_end_request(clone = ?, error = 0)
-008|dm_done(inline)
-008|dm_softirq_done()
-009|blk_done_softirq()
-010|__read_once_size(inline)
-010|static_key_count(inline)
-010|static_key_false(inline)
-010|trace_softirq_exit(inline)
-010|__do_softirq()
-011|do_softirq_own_stack(inline)
-011|invoke_softirq(inline) <-- softirq is triggered because 
scsi_request_fn (-016) enabled interrupts on this cpu

-011|irq_exit()
-012|handle_IPI()
-013|gic_handle_irq()
-014|el1_irq(asm)
 -->|exception
-015|__raw_spin_unlock_irq(inline)
-015|raw_spin_unlock_irq(lock = ?)
-016|scsi_request_fn() <-- Unlocks the queue using spin_unlock, doesn't 
restore the flags, thus enabling the interrupts

-017|__blk_run_queue_uncond(inline)
-017|__blk_run_queue(q = ?)
-018|__elv_add_request()
-019|blk_insert_cloned_request() <-- acquires the queue lock & saves the 
flags

-020|dm_dispatch_clone_request(clone = ?, rq = ?)
-021|map_request()
-022|dm_request_fn()
-023|__blk_run_queue_uncond(inline)
-023|__blk_run_queue
-024|spin_unlock_irq(inline)
-024|blk_delay_work(?) <-- also acquires a queue lock, but this is a 
different queue, blk_end_request_all will reference this queue

-025|__read_once_size(inline)
-025|static_key_count(inline)
-025|static_key_false(inline)
-025|trace_workqueue_execute_end(inline)
-025|process_one_work()
-026|worker_thread()
-027|kthread()
-028|ret_from_fork(asm)
 ---|end of frame

Please can you check if this is actually a bug and my understanding is 
correct.
If so, I can put up a patch for the same.

--
Asutosh Das (asd)

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