From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "tj@kernel.org" <tj@kernel.org>
Cc: "jthumshirn@suse.de" <jthumshirn@suse.de>,
"hch@lst.de" <hch@lst.de>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
"ming.lei@redhat.com" <ming.lei@redhat.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"martin@lichtvoll.de" <martin@lichtvoll.de>,
"oleksandr@natalenko.name" <oleksandr@natalenko.name>,
"hare@suse.com" <hare@suse.com>,
"jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>
Subject: Re: [PATCH] Change synchronize_rcu() in scsi_device_quiesce() into synchronize_sched()
Date: Mon, 19 Mar 2018 15:16:07 +0000 [thread overview]
Message-ID: <1521472566.2776.6.camel@wdc.com> (raw)
In-Reply-To: <20180319143147.GF2943022@devbig577.frc2.facebook.com>
On Mon, 2018-03-19 at 07:31 -0700, Tejun Heo wrote:
> On Fri, Mar 16, 2018 at 10:35:16AM -0700, Bart Van Assche wrote:
> > Since blk_queue_enter() uses rcu_read_lock_sched() scsi_device_quiesce()
> > must use synchronize_sched().
>
> Is there a reason to use sched-RCU here instead of the regular one?
> If not, it'd be better to switch to regular RCU than the other way
> around.
Hello Tejun,
As explained in the comment in scsi_device_quiesce(), the effect of
blk_set_preempt_only() must be visible for percpu_ref_tryget() calls that
occur after the queue unfreeze triggered by scsi_device_quiesce(). Hence the
RCU read lock calls in blk_queue_enter(). Since these RCU read lock calls
surround a function call that uses rcu_read_lock_sched(), namely
percpu_ref_tryget_live(), we have to use sched-RCU in both blk_queue_enter()
and scsi_device_quiesce().
Bart.
next prev parent reply other threads:[~2018-03-19 15:16 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-16 17:35 [PATCH] Change synchronize_rcu() in scsi_device_quiesce() into synchronize_sched() Bart Van Assche
2018-03-16 21:42 ` Martin Steigerwald
2018-03-16 21:42 ` Martin Steigerwald
2018-03-16 21:51 ` Bart Van Assche
2018-03-19 9:02 ` Martin Steigerwald
2018-03-19 14:31 ` Tejun Heo
2018-03-19 15:16 ` Bart Van Assche [this message]
2018-03-19 15:21 ` tj
2018-03-19 16:18 ` Bart Van Assche
2018-03-19 16:29 ` tj
2018-03-19 16:57 ` Bart Van Assche
2018-03-19 17:02 ` tj
2018-03-19 20:19 ` Bart Van Assche
2018-03-19 20:19 ` Bart Van Assche
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