linux-kernel - Re: [RFC 0/6] migrate_pages(): batch TLB flushing

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Date:   Tue, 27 Sep 2022 16:16:42 +0530
From:   Bharata B Rao <bharata@....com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Oscar Salvador <osalvador@...e.de>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC 0/6] migrate_pages(): batch TLB flushing

On 9/23/2022 1:22 PM, Huang, Ying wrote:
> Bharata B Rao <bharata@....com> writes:
>>
>> Thanks for the patchset. I find it hitting the following BUG() when
>> running mmtests/autonumabench:
>>
>> kernel BUG at mm/migrate.c:2432!
>>
>> This is BUG_ON(!list_empty(&migratepages)) in migrate_misplaced_page().
> 
> Thank you very much for reporting!  I haven't reproduced this yet.  But
> I will pay special attention to this when develop the next version, even
> if I cannot reproduce this finally.

The following change fixes the above reported BUG_ON().

diff --git a/mm/migrate.c b/mm/migrate.c
index a0de0d9b4d41..c11dd82245e5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1197,7 +1197,7 @@ static int migrate_page_unmap(new_page_t get_new_page, free_page_t put_new_page,
         * references and be restored.
         */
        /* restore the page to right list. */
-       if (rc != -EAGAIN)
+       if (rc == -EAGAIN)
                 ret = NULL;
 
        migrate_page_undo_page(page, page_was_mapped, anon_vma, locked, ret);

The pages that returned from unmapping stage with -EAGAIN used to
end up on "ret" list rather than continuing on the "from" list.

Regards,
Bharata.