From: Keith Busch <keith.busch@intel.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Ashok Raj <ashok.raj@intel.com>,
linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH 3/3] pciehp: Fix race condition handling surprise link-down
Date: Wed, 7 Dec 2016 19:04:33 -0500 [thread overview]
Message-ID: <20161208000433.GD25959@localhost.localdomain> (raw)
In-Reply-To: <20161207234054.GL22129@bhelgaas-glaptop.roam.corp.google.com>
On Wed, Dec 07, 2016 at 05:40:54PM -0600, Bjorn Helgaas wrote:
> On Sat, Nov 19, 2016 at 12:32:47AM -0800, Ashok Raj wrote:
> > --- a/drivers/pci/hotplug/pciehp_ctrl.c
> > +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> > @@ -182,6 +182,7 @@ static void pciehp_power_thread(struct work_struct *work)
> > switch (info->req) {
> > case DISABLE_REQ:
> > mutex_lock(&p_slot->hotplug_lock);
> > + p_slot->state = POWEROFF_STATE;
>
> It sounds right that p_slot->state should be protected.
>
> It looks like handle_button_press_event() and
> pciehp_sysfs_enable_slot() hold p_slot->lock while updating
> p_slot->state.
>
> You're setting "state = POWEROFF_STATE" while holding
> p_slot->hotplug_lock (not p_slot->lock). Four lines down, we set
> "state = STATIC_STATE", but this time we're holding p_slot->lock.
>
> What is the difference between the p_slot->lock and
> p_slot->hotplug_lock? Do we need both? How do we know which one to
> use?
>
> I'm very confused.
This is _very_ confusing. :)
The p_slot->hotplug_lock serializes a power off and a power on event. We
only want to set the state when one of those events gets to execute
rather than when the event is queued. Changing the state when the event
is queued can trigger a never ending up-down sequence.
It currently looks safe to nest the p_slot->lock under the
p_slot->hotplug_lock if that is you recommendation.
Alternatively we could fix this if we used an ordered work queue for
the slot's work, but that is a significantly more complex change.
next prev parent reply other threads:[~2016-12-07 23:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-19 8:32 [PATCH 0/3] Fix improper handling of pcie hotplug events Ashok Raj
2016-11-19 8:32 ` [PATCH 1/3] pciehp: Prioritize data-link event over presence detect Ashok Raj
2016-11-19 8:32 ` [PATCH 2/3] pciehp: Fix led status when enabling already enabled slot Ashok Raj
2016-11-19 8:32 ` [PATCH 3/3] pciehp: Fix race condition handling surprise link-down Ashok Raj
2016-12-07 23:40 ` Bjorn Helgaas
2016-12-08 0:04 ` Keith Busch [this message]
2016-12-08 15:11 ` Bjorn Helgaas
2016-12-08 17:20 ` Keith Busch
2016-12-08 17:50 ` Bjorn Helgaas
2016-12-09 21:11 ` Raj, Ashok
2016-12-07 23:31 ` [PATCH 0/3] Fix improper handling of pcie hotplug events Bjorn Helgaas
2016-12-08 18:05 ` Bjorn Helgaas
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