linux-kernel - Re: [RFC PATCH 2/3] PM / Runtime: force memory allocation with no I/O during runtime

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Date:	Mon, 15 Oct 2012 22:35:50 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-pm@...r.kernel.org,
	Oliver Neukum <oneukum@...e.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [RFC PATCH 2/3] PM / Runtime: force memory allocation with no I/O
 during runtime_resume callbcack

On Mon, Oct 15, 2012 at 10:14 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Mon, 15 Oct 2012, Ming Lei wrote:
>
>> 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@...land.harvard.edu>
>> Cc: Oliver Neukum <oneukum@...e.de>
>> Cc: Rafael J. Wysocki <rjw@...k.pl>
>> Signed-off-by: Ming Lei <ming.lei@...onical.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);
>
> This is not so good.  What happens if I/O was already forbidden when
> this function was called?

You are right, the old flag should be saved before forbidding and restored
after allowing.

Thanks,
--
Ming Lei
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