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Date: Tue, 27 Nov 2012 22:19:29 +0100
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: linux-pm@...r.kernel.org
Cc: Ming Lei <ming.lei@...onical.com>, linux-kernel@...r.kernel.org,
Alan Stern <stern@...land.harvard.edu>,
Oliver Neukum <oneukum@...e.de>,
Minchan Kim <minchan@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jens Axboe <axboe@...nel.dk>,
"David S. Miller" <davem@...emloft.net>,
Andrew Morton <akpm@...ux-foundation.org>,
netdev@...r.kernel.org, linux-usb@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v6 2/6] PM / Runtime: introduce pm_runtime_set_memalloc_noio()
On Saturday, November 24, 2012 08:59:14 PM Ming Lei wrote:
> The patch introduces the flag of memalloc_noio in 'struct dev_pm_info'
> to help PM core to teach mm not allocating memory with GFP_KERNEL
> flag for avoiding probable deadlock.
>
> As explained in the comment, any GFP_KERNEL allocation inside
> runtime_resume() or runtime_suspend() on any one of device in
> the path from one block or network device to the root device
> in the device tree may cause deadlock, the introduced
> pm_runtime_set_memalloc_noio() sets or clears the flag on
> device in the path recursively.
>
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: "Rafael J. Wysocki" <rjw@...k.pl>
> Signed-off-by: Ming Lei <ming.lei@...onical.com>
> ---
> v5:
> - fix code style error
> - add comment on clear the device memalloc_noio flag
> v4:
> - rename memalloc_noio_resume as memalloc_noio
> - remove pm_runtime_get_memalloc_noio()
> - add comments on pm_runtime_set_memalloc_noio
> v3:
> - introduce pm_runtime_get_memalloc_noio()
> - hold one global lock on pm_runtime_set_memalloc_noio
> - hold device power lock when accessing memalloc_noio_resume
> flag suggested by Alan Stern
> - implement pm_runtime_set_memalloc_noio without recursion
> suggested by Alan Stern
> v2:
> - introduce pm_runtime_set_memalloc_noio()
> ---
> drivers/base/power/runtime.c | 60 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/pm.h | 1 +
> include/linux/pm_runtime.h | 3 +++
> 3 files changed, 64 insertions(+)
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 3148b10..3e198a0 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -124,6 +124,66 @@ unsigned long pm_runtime_autosuspend_expiration(struct device *dev)
> }
> EXPORT_SYMBOL_GPL(pm_runtime_autosuspend_expiration);
>
> +static int dev_memalloc_noio(struct device *dev, void *data)
> +{
> + return dev->power.memalloc_noio;
> +}
> +
> +/*
> + * pm_runtime_set_memalloc_noio - Set a device's memalloc_noio flag.
> + * @dev: Device to handle.
> + * @enable: True for setting the flag and False for clearing the flag.
> + *
> + * Set the flag for all devices in the path from the device to the
> + * root device in the device tree if @enable is true, otherwise clear
> + * the flag for devices in the path whose siblings don't set the flag.
> + *
Please use counters instead of walking the whole path every time. Ie. in
addition to the flag add a counter to store the number of the device's
children having that flag set.
Besides, don't you need to check children for the arg device itself?
> + * The function should only be called by block device, or network
> + * device driver for solving the deadlock problem during runtime
> + * resume/suspend:
> + *
> + * If memory allocation with GFP_KERNEL is called inside runtime
> + * resume/suspend callback of any one of its ancestors(or the
> + * block device itself), the deadlock may be triggered inside the
> + * memory allocation since it might not complete until the block
> + * device becomes active and the involed page I/O finishes. The
> + * situation is pointed out first by Alan Stern. Network device
> + * are involved in iSCSI kind of situation.
> + *
> + * The lock of dev_hotplug_mutex is held in the function for handling
> + * hotplug race because pm_runtime_set_memalloc_noio() may be called
> + * in async probe().
> + *
> + * The function should be called between device_add() and device_del()
> + * on the affected device(block/network device).
> + */
> +void pm_runtime_set_memalloc_noio(struct device *dev, bool enable)
> +{
> + static DEFINE_MUTEX(dev_hotplug_mutex);
What's the mutex for?
> +
> + mutex_lock(&dev_hotplug_mutex);
> + for (;;) {
> + /* hold power lock since bitfield is not SMP-safe. */
> + spin_lock_irq(&dev->power.lock);
> + dev->power.memalloc_noio = enable;
> + spin_unlock_irq(&dev->power.lock);
> +
> + dev = dev->parent;
> +
> + /*
> + * clear flag of the parent device only if all the
> + * children don't set the flag because ancestor's
> + * flag was set by any one of the descendants.
> + */
> + if (!dev || (!enable &&
> + device_for_each_child(dev, NULL,
> + dev_memalloc_noio)))
> + break;
> + }
> + mutex_unlock(&dev_hotplug_mutex);
> +}
> +EXPORT_SYMBOL_GPL(pm_runtime_set_memalloc_noio);
> +
> /**
> * rpm_check_suspend_allowed - Test whether a device may be suspended.
> * @dev: Device to test.
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 03d7bb1..1a8a69d 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -538,6 +538,7 @@ struct dev_pm_info {
> unsigned int irq_safe:1;
> unsigned int use_autosuspend:1;
> unsigned int timer_autosuspends:1;
> + unsigned int memalloc_noio:1;
> enum rpm_request request;
> enum rpm_status runtime_status;
> int runtime_error;
> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index f271860..775e063 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -47,6 +47,7 @@ extern void pm_runtime_set_autosuspend_delay(struct device *dev, int delay);
> extern unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
> extern void pm_runtime_update_max_time_suspended(struct device *dev,
> s64 delta_ns);
> +extern void pm_runtime_set_memalloc_noio(struct device *dev, bool enable);
>
> static inline bool pm_children_suspended(struct device *dev)
> {
> @@ -149,6 +150,8 @@ static inline void pm_runtime_set_autosuspend_delay(struct device *dev,
> int delay) {}
> static inline unsigned long pm_runtime_autosuspend_expiration(
> struct device *dev) { return 0; }
> +static inline void pm_runtime_set_memalloc_noio(struct device *dev,
> + bool enable){}
>
> #endif /* !CONFIG_PM_RUNTIME */
>
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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