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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

  reply	other threads:[~2018-03-19 15:21 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
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
2018-03-19 20:19                 ` Bart Van Assche

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