[dm-devel] [PATCH] md: fix bug due to nested suspend

[NeilBrown]

On Thu, Dec 17 2015, Mikulas Patocka wrote:

> On Wed, 16 Dec 2015, NeilBrown wrote:
>
>> On Thu, Nov 26 2015, Mikulas Patocka wrote:
>> 
>> > The patch c7bfced9a6716ff66c9d61f934bb60af08d4688c committed to 4.4-rc 
>> > causes crash in LVM test shell/lvchange-raid.sh. The kernel crashes with 
>> > this BUG, the reason is that we attempt to suspend a device that is 
>> > already suspended. See also 
>> > https://bugzilla.redhat.com/show_bug.cgi?id=1283491
>> >
>> > This patch fixes the bug by introducing functions mddev_nested_suspend and
>> > mddev_nested_resume that can be called when the device is already
>> > suspended. The number of calls to mddev_nested_suspend is kept in the
>> > variable mddev->suspended.
>> 
>> Hi,
>>  thanks for the report and patch.
>> 
>> I think I would rather just make mddev_suspend() always nest.
>> It is always called under ->reconfig_mutex or some similar guarentee of
>> being single-threaded in dm-raid, so we don't need an atomic_t.
>> 
>> Just
>>   mddev_suspend()
>> 	if (mddev->suspended++)
>>         	return;
>>         ...do the suspend.
>> 
>> and
>>   mddev_resume()
>>        if (--mddev->suspended)
>>        		return;
>>        ... to the resume
>> 
>> Does that seem reasonable to you?
>
> Yes, it seems OK.
>
> Mikulas

Thanks.  I've revised your original patch to behave as above and will
send to Linus today or tomorrow.

Thanks,
NeilBrown
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