On Tuesday 30 October 2012 11:21:33 Ming Lei wrote:

On Mon, Oct 29, 2012 at 11:41 PM, Alan Stern [off-list ref] wrote:

quoted

On Mon, 29 Oct 2012, Ming Lei wrote:

quoted

The patch introduces the flag of memalloc_noio_resume in
'struct dev_pm_info' to help PM core to teach mm not allocating
memory with GFP_KERNEL flag for avoiding probable deadlock
problem.

As explained in the comment, any GFP_KERNEL allocation inside
runtime_resume 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 of the path recursively.

This patch also introduces pm_runtime_get_memalloc_noio() because
the flag may be accessed in block device's error handling path
(for example, usb device reset)

quoted

+/*
+ * pm_runtime_get_memalloc_noio - Get a device's memalloc_noio flag.
+ * @dev: Device to handle.
+ *
+ * Return the device's memalloc_noio flag.
+ *
+ * The device power lock is held because bitfield is not SMP-safe.
+ */
+bool pm_runtime_get_memalloc_noio(struct device *dev)
+{
+     bool ret;
+     spin_lock_irq(&dev->power.lock);
+     ret = dev->power.memalloc_noio_resume;
+     spin_unlock_irq(&dev->power.lock);
+     return ret;
+}

You don't need to acquire and release a spinlock just to read the
value.  Reading bitfields _is_ SMP-safe; writing them is not.

Thanks for your review.

As you pointed out before, the flag need to be checked before
resetting usb devices, so the lock should be held to make another
context(CPU) see the updated value suppose one context(CPU)
call pm_runtime_set_memalloc_noio() to change the flag at the
same time.

The lock needn't to be held when the function is called inside
pm_runtime_set_memalloc_noio(),  so the bitfield flag should
be checked directly without holding power lock in dev_memalloc_noio().

Hi,

how is this to work with power management domains?
And I may be dense, but disks are added in slave_configure().
This seems to be a race to me.

	Regards
		Oliver