Re: [PATCH v2] mm/hugetlb: defer free_huge_page() to a workqueue

[Michal Hocko]

On Thu 12-12-19 11:04:27, 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.

I am afraid that work_struct is too large to be stuffed into the struct
page array (because of the lockdep part).

I think that it would be just safer to make hugetlb_lock irq safe. Are
there any other locks that would require the same?
-- 
Michal Hocko
SUSE Labs