From mboxrd@z Thu Jan  1 00:00:00 1970
From: Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH] scsi: fix scsi_error_handler vs. scsi_host_dev_release
 race
Date: Fri, 28 Aug 2015 08:40:38 +0200
Message-ID: <55E00266.8030809@suse.de>
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To: mhocko@kernel.org, "James E.J. Bottomley" <JBottomley@odin.com>
Cc: Dan Williams <dan.j.williams@intel.com>, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Michal Hocko <mhocko@suse.com>
List-Id: linux-scsi@vger.kernel.org

On 08/27/2015 08:16 PM, mhocko@kernel.org wrote:
> From: Michal Hocko <mhocko@suse.com>
>=20
> b9d5c6b7ef57 ("[SCSI] cleanup setting task state in
> scsi_error_handler()") has introduced a race between scsi_error_handl=
er
> and scsi_host_dev_release resulting in the hang when the device goes
> away because scsi_error_handler might miss a wake up:
>=20
> CPU0					CPU1
> scsi_error_handler			scsi_host_dev_release
>   					  kthread_stop()
>   kthread_should_stop()
>     test_bit(KTHREAD_SHOULD_STOP)
> 					    set_bit(KTHREAD_SHOULD_STOP)
> 					    wake_up_process()
> 					    wait_for_completion()
>=20
>   set_current_state(TASK_INTERRUPTIBLE)
>   schedule()
>=20
> The most straightforward solution seems to be to invert the ordering =
of
> the set_current_state and kthread_should_stop.
>=20
> The issue has been noticed during reboot test on a 3.0 based kernel b=
ut
> the current code seems to be affected in the same way.
>=20
> Cc: stable # 3.6+
> Reported-and-Debugged-by: Mike Mayer <Mike.Meyer@teradata.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  drivers/scsi/scsi_error.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>=20
> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
> index 6457a8a0db9c..2c0a817d5dbe 100644
> --- a/drivers/scsi/scsi_error.c
> +++ b/drivers/scsi/scsi_error.c
> @@ -2169,8 +2169,11 @@ int scsi_error_handler(void *data)
>  	 * We never actually get interrupted because kthread_run
>  	 * disables signal delivery for the created thread.
>  	 */
> -	while (!kthread_should_stop()) {
> +	while (true) {
>  		set_current_state(TASK_INTERRUPTIBLE);
> +		if (kthread_should_stop())
> +			break;
> +
>  		if ((shost->host_failed =3D=3D 0 && shost->host_eh_scheduled =3D=3D=
 0) ||
>  		    shost->host_failed !=3D atomic_read(&shost->host_busy)) {
>  			SCSI_LOG_ERROR_RECOVERY(1,
>=20
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
--=20
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.de			               +49 911 74053 688
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