linux-kernel - RE: sata_mv port lockup on hotplug (kernel 2.6.38.2)

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Date:	Tue, 6 Sep 2011 15:40:44 +0100
From:	Bruce Stenning <b.stenning@...igovision.com>
To:	Tejun Heo <htejun@...il.com>
CC:	Mark Lord <kernel@...savvy.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	Jeff Garzik <jgarzik@...ox.com>
Subject: RE: sata_mv port lockup on hotplug (kernel 2.6.38.2)

I wrote:
> Is it attempting to wake the scsi_eh_3 thread while scsi_error_handler
> is still processing an EH, which then calls scsi_restart_operations and
> puts the scsi_eh_3 thread back to sleep again?

It does look to me as if there is a potential race between the scsi_eh thread
and the wake-up mechanism.

host_eh_scheduled is read here in scsi_error_handler:

        set_current_state(TASK_INTERRUPTIBLE);
        while (!kthread_should_stop()) {
                if ((shost->host_failed == 0 && shost->host_eh_scheduled == 0) ||

For scheduling an EH, scsi_schedule_eh takes the shost->host_lock, increments
shost->host_eh_scheduled, and then wakes the EH thread.  If this happens
between the scsi_eh thread reading host_eh_scheduled and sending itself to
sleep, then nothing will wake up the thread and host_eh_scheduled will not
be inspected again.

Is there some mechanism that I've missed to prevent this from happening?

Bruce.

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