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SubjectRe: [PATCH] pciehp: Fix race condition handling surprise link-down
Hi Keith

did you have a chance to look at this?

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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