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SubjectRe: [PATCH] pciehp: Fix race condition handling surprise link-down
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@google.com>
> > Cc: linux-kernel@vger.kernel.org
> > Cc: Keith Busch <keith.busch@intel.com>
> >
> > Signed-off-by: Ashok Raj <ashok.raj@intel.com>
> > Reviewed-by: Keith Busch <keith.busch@intel.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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