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SubjectRe: [RFC PATCH 2/3] PM / Runtime: force memory allocation with no I/O during runtime_resume callbcack
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On Mon, Oct 15, 2012 at 10:14 PM, Alan Stern <stern@rowland.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@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);
>
> 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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