Message-ID: <c98a3741-273b-8a69-016d-5f3e79f8a71e@acm.org>
Date:   Tue, 14 Mar 2023 16:21:15 -0700
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Subject: Re: [REGRESSION] CPUIDLE_FLAG_RCU_IDLE, blk_mq_freeze_queue_wait()
 and slow-stuck reboots
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To:     Alexey Klimov <alexey.klimov@linaro.org>, peterz@infradead.org
Cc:     draszik@google.com, peter.griffin@linaro.org,
        willmcvicker@google.com, mingo@kernel.org, ulf.hansson@linaro.org,
        tony@atomide.com, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, axboe@kernel.dk,
        alim.akhtar@samsung.com, regressions@lists.linux.dev,
        avri.altman@wdc.com, klimova@google.com
References: <20230314230004.961993-1-alexey.klimov@linaro.org>
From:   Bart Van Assche <bvanassche@acm.org>
In-Reply-To: <20230314230004.961993-1-alexey.klimov@linaro.org>
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Precedence: bulk

On 3/14/23 16:00, Alexey Klimov wrote:
> The delay is found to be in device's ->shutdown() methods called from kernel_restart():
> void kernel_restart_prepare(char *cmd)
> {
> 	blocking_notifier_call_chain(&reboot_notifier_list, SYS_RESTART, cmd);
> 	system_state = SYSTEM_RESTART;
> 	usermodehelper_disable();
> 	device_shutdown();	<---- here
> }
> 
> The driver in question is ufshcd and its ufshcd_wl_shutdown() shutdown method. It often blocks on scsi_device_quiesce() and upon manual checking it seems that it sleeps on blk_mq_freeze_queue_wait()/wait_event() in blk_freeze_queue():
> 
> scsi_device_quiesce(struct scsi_device *sdev)
> {
> 	...
> 	blk_mq_freeze_queue(q);
> 	...
> }
> 	||
> 	V
> void blk_freeze_queue(struct request_queue *q)
> {
> 	/*
> 	 * In the !blk_mq case we are only calling this to kill the
> 	 * q_usage_counter, otherwise this increases the freeze depth
> 	 * and waits for it to return to zero.  For this reason there is
> 	 * no blk_unfreeze_queue(), and blk_freeze_queue() is not
> 	 * exported to drivers as the only user for unfreeze is blk_mq.
> 	 */
> 	blk_freeze_queue_start(q);
> 	blk_mq_freeze_queue_wait(q);	<--- sleeps on wait_event() here
> }

Please let me know if you want me to resubmit patch "scsi: ufs: Remove 
the LUN quiescing code from ufshcd_wl_shutdown()" 
(https://lore.kernel.org/linux-scsi/20220331223424.1054715-14-bvanassche@acm.org/).

Thanks,

Bart.