On 12/16/19 8:26 AM, Michal Hocko wrote: > On Thu 12-12-19 15:52:20, Waiman Long wrote: >> On 12/12/19 2:22 PM, Mike Kravetz wrote: >>> On 12/12/19 11:04 AM, Davidlohr Bueso wrote: >>>> There have been deadlock reports[1, 2] where put_page is called >>>> from softirq context and this causes trouble with the hugetlb_lock, >>>> as well as potentially the subpool lock. >>>> >>>> For such an unlikely scenario, lets not add irq dancing overhead >>>> to the lock+unlock operations, which could incur in expensive >>>> instruction dependencies, particularly when considering hard-irq >>>> safety. For example PUSHF+POPF on x86. >>>> >>>> Instead, just use a workqueue and do the free_huge_page() in regular >>>> task context. >>>> >>>> [1] https://lore.kernel.org/lkml/20191211194615.18502-1-longman@xxxxxxxxxx/ >>>> [2] https://lore.kernel.org/lkml/20180905112341.21355-1-aneesh.kumar@xxxxxxxxxxxxx/ >>>> >>>> Reported-by: Waiman Long <longman@xxxxxxxxxx> >>>> Reported-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> >>>> Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx> >>> Thank you Davidlohr. >>> >>> The patch does seem fairly simple and straight forward. I need to brush up >>> on my workqueue knowledge to provide a full review. >>> >>> Longman, >>> Do you have a test to reproduce the issue? If so, can you try running with >>> this patch. >> Yes, I do have a test that can reproduce the issue. I will run it with >> the patch and report the status tomorrow. > Can you extract guts of the testcase and integrate them into hugetlb > test suite? The test case that I used is the Red Hat internal "Fork vs. fast GUP race test" written by Jarod Wilson. I would have to ask him if he is OK with that. Cheers, Longman
