linux-kernel - Re: [PATCH] pciehp: Fix race condition handling surprise link-down

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Message-ID: <20170119143441.GA12124@bhelgaas-glaptop.roam.corp.google.com>
Date:   Thu, 19 Jan 2017 08:34:41 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Keith Busch <keith.busch@...el.com>
Cc:     "Raj, Ashok" <ashok.raj@...el.com>, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pciehp: Fix race condition handling surprise link-down

Sorry for the delay, I'm just trying to clear out some of our defects from
bugzilla and have gotten really behind on the list, so I just haven't
gotten to this yet.

On Wed, Jan 18, 2017 at 01:47:11PM -0500, Keith Busch wrote:
> Hi Bjorn,
> 
> This fix looks good to me as well now. Any other concerns before staging
> this one for inclusion?
> 
> Thanks,
> Keith
> 
> On Tue, Jan 17, 2017 at 11:15:40AM -0800, Raj, Ashok wrote:
> > Hi Bjorn
> > 
> > Sorry to bug you, didn't hear from you after i added the lock for consistency
> > to address the feedback.
> > 
> > Let me know if there is anymore changes you like to see.
> > 
> > Cheers,
> > Ashok
> > 
> > On Fri, Dec 09, 2016 at 01:06:04PM -0800, Ashok Raj wrote:
> > > Changes from v1:
> > > 	Address comments from Bjorn:
> > > 		Added p_slot->lock mutex around changes to p_slot->state
> > > 		Updated commit message to call out mutex names
> > > 
> > > A surprise link down may retrain very quickly, causing the same slot to
> > > generate a link up event before handling the link down completes.
> > > 
> > > Since the link is active, the power off work queued from the first link
> > > down will cause a second down event when the power is disabled. The second
> > > down event should be ignored because the slot is already powering off;
> > > however, the "link up" event sets the slot state to POWERON before the
> > > event to handle this is enqueued, making the second down event believe
> > > it needs to do something. This creates a constant link up and down
> > > event cycle.
> > > 
> > > This patch fixes that by setting the p_slot->state only when the work to
> > > handle the power event is executing, protected by the p_slot->hotplug_lock.
> > > 
> > > To: Bjorn Helgass <bhelgaas@...gle.com>
> > > Cc: linux-kernel@...r.kernel.org
> > > Cc: Keith Busch <keith.busch@...el.com>
> > > 
> > > Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> > > Reviewed-by: Keith Busch <keith.busch@...el.com>
> > > ---
> > >  drivers/pci/hotplug/pciehp_ctrl.c | 8 ++++++--
> > >  1 file changed, 6 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> > > index ec0b4c1..4cf4772 100644
> > > --- a/drivers/pci/hotplug/pciehp_ctrl.c
> > > +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> > > @@ -182,6 +182,9 @@ static void pciehp_power_thread(struct work_struct *work)
> > >  	switch (info->req) {
> > >  	case DISABLE_REQ:
> > >  		mutex_lock(&p_slot->hotplug_lock);
> > > +		mutex_lock(&p_slot->lock);
> > > +		p_slot->state = POWEROFF_STATE;
> > > +		mutex_unlock(&p_slot->lock);
> > >  		pciehp_disable_slot(p_slot);
> > >  		mutex_unlock(&p_slot->hotplug_lock);
> > >  		mutex_lock(&p_slot->lock);
> > > @@ -190,6 +193,9 @@ static void pciehp_power_thread(struct work_struct *work)
> > >  		break;
> > >  	case ENABLE_REQ:
> > >  		mutex_lock(&p_slot->hotplug_lock);
> > > +		mutex_lock(&p_slot->lock);
> > > +		p_slot->state = POWERON_STATE;
> > > +		mutex_unlock(&p_slot->lock);
> > >  		ret = pciehp_enable_slot(p_slot);
> > >  		mutex_unlock(&p_slot->hotplug_lock);
> > >  		if (ret)
> > > @@ -209,8 +215,6 @@ static void pciehp_queue_power_work(struct slot *p_slot, int req)
> > >  {
> > >  	struct power_work_info *info;
> > >  
> > > -	p_slot->state = (req == ENABLE_REQ) ? POWERON_STATE : POWEROFF_STATE;
> > > -
> > >  	info = kmalloc(sizeof(*info), GFP_KERNEL);
> > >  	if (!info) {
> > >  		ctrl_err(p_slot->ctrl, "no memory to queue %s request\n",
> > > -- 
> > > 2.7.4
> --
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