From: "tj@kernel.org" <tj@kernel.org>
To: Bart Van Assche <Bart.VanAssche@wdc.com>
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 08:21:44 -0700 [thread overview]
Message-ID: <20180319152144.GM2943022@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <1521472566.2776.6.camel@wdc.com>
Hello,
On Mon, Mar 19, 2018 at 03:16:07PM +0000, Bart Van Assche wrote:
> 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().
Let's please not depend on rcu_read_lock_sched() in
percpu_ref_tryget_live(). That's an implementation detail. If the
code needs RCU based synchronization, it should perform them
explicitly.
Thanks.
--
tejun
next prev parent reply other threads:[~2018-03-19 15:21 UTC|newest]
Thread overview: 12+ 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 21:51 ` 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
2018-03-19 15:21 ` tj [this message]
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
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