[RFC PATCH 2/3] PM / Runtime: force memory allocation with no I/O during runtime_resume callbcack

[Ming Lei <ming.lei@canonical.com>]

This patch applies the introduces tsk_memalloc_forbid_io() and
tsk_memalloc_allow_io() to force memory allocation with no I/O
during runtime_resume callback.

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Oliver Neukum <oneukum@suse.de>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
 drivers/base/power/runtime.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 3148b10..76836c1 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -652,7 +652,20 @@ static int rpm_resume(struct device *dev, int rpmflags)
 	if (!callback && dev->driver && dev->driver->pm)
 		callback = dev->driver->pm->runtime_resume;
 
+	/*
+	 * Deadlock might be caused if memory allocation with GFP_KERNEL
+	 * happens inside runtime_resume callback of one block device's
+	 * ancestor or the block device itself. The easiest approach is
+	 * to forbid I/O inside runtime_resume of all devices.
+	 *
+	 * In fact, it can be done only if the deivce is a block device
+	 * or there is one block device descendant. But that may become
+	 * complicated and not efficient because device tree traversing
+	 * is involved.
+	 */
+	tsk_memalloc_forbid_io(current);
 	retval = rpm_callback(callback, dev);
+	tsk_memalloc_allow_io(current);
 	if (retval) {
 		__update_runtime_status(dev, RPM_SUSPENDED);
 		pm_runtime_cancel_pending(dev);
-- 
1.7.9.5