Re: Re: [PATCH v2] mm/page_alloc: fix alloc_pages_bulk/set_page_owner panic on irq disabled

From: Mel Gorman
Date: Thu Jul 15 2021 - 10:05:45 EST

On Thu, Jul 15, 2021 at 09:02:14PM +0800, ?????? wrote:
> >> Fixes: 0f87d9d30f21 ("mm/page_alloc: add an array-based interface to the bulk page allocator")
> >> Reported-by: syzbot+b07d8440edb5f8988eea@xxxxxxxxxxxxxxxxxxxxxxxxx
> >> Suggested-by: Wang Qing <wangqing@xxxxxxxx>
> >> Signed-off-by: Yang Huan <link@xxxxxxxx>
> >
> >
> >is now part of a series that has being sent to Linus. Hence, the Fixes
> >part is no longer applicable and the patch will no longer be addresing
> >an atomic sleep bug. This patch should be treated as an enhancement
> Hi Mel Gorman, thanks for your reply.
> I see the fix patch, it fix this bug by abandon alloc bulk feature when page_owner is set.
> But in my opinion, it can't really fix this bug, it's a circumvention plan.

Yes, it's a circumvention plan for reasons as laid out in the changelog.

> >to allow bulk allocations when PAGE_OWNER is set. For that, it should
> >include a note on the performance if PAGE_OWNER is used with either NFS
> >or high-speed networking to justify the additional complexity.
> My patch just split the prep_new_page page_gfp into alloc_gfp(for alloc bulk is GFP_ATOMIC,
> for other's no change) and trace page gfp. So, we will not use the error way to get memory.
> So, I think this will not affect alloc bulk performance when page_owner is on(compare with origin patch) but
> can really fix this bug rather than evade.
> And this patch can let alloc bulk feature and page_owner feature work togher
> So, I will send patch again based on the fix patch.

Your fix should revert the workaround. Also your changelog should note
that in some cases that PAGE_OWNER information will be lost if the
GFP_ATOMIC allocation from bulk allocation context fails.

Mel Gorman