From: Matthew Wilcox <willy@infradead.org>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Zhang Yi <wetpzy@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>,
Mike Kravetz <mike.kravetz@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Neel Natu <neelnatu@google.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm, futex: Fix shared futex pgoff on shmem huge page
Date: Sun, 13 Jun 2021 11:27:26 +0100 [thread overview]
Message-ID: <YMXdjhwpRzP6r8Uj@casper.infradead.org> (raw)
In-Reply-To: <b17d946b-d09-326e-b42a-52884c36df32@google.com>
On Sat, Jun 12, 2021 at 08:16:58PM -0700, Hugh Dickins wrote:
> If more than one futex is placed on a shmem huge page, it can happen that
> waking the second wakes the first instead, and leaves the second waiting:
> the key's shared.pgoff is wrong.
>
> When 3.11 commit 13d60f4b6ab5 ("futex: Take hugepages into account when
> generating futex_key"), the only shared huge pages came from hugetlbfs,
> and the code added to deal with its exceptional page->index was put into
> hugetlb source. Then that was missed when 4.8 added shmem huge pages.
>
> page_to_pgoff() is what others use for this nowadays: except that, as
> currently written, it gives the right answer on hugetlbfs head, but
> nonsense on hugetlbfs tails. Fix that by calling hugetlbfs-specific
> hugetlb_basepage_index() on PageHuge tails as well as on head.
>
> Yes, it's unconventional to declare hugetlb_basepage_index() there in
> pagemap.h, rather than in hugetlb.h; but I do not expect anything but
> page_to_pgoff() ever to need it.
>
> Fixes: 800d8c63b2e9 ("shmem: add huge pages support")
> Reported-by: Neel Natu <neelnatu@google.com>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> Cc: <stable@vger.kernel.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
next prev parent reply other threads:[~2021-06-13 10:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-12 4:31 [PATCH] mm, futex: Fix shared futex pgoff on shmem huge page Hugh Dickins
2021-06-12 16:15 ` Matthew Wilcox
2021-06-13 3:14 ` Hugh Dickins
2021-06-13 3:16 ` [PATCH v2] " Hugh Dickins
2021-06-13 10:27 ` Matthew Wilcox [this message]
2021-06-15 14:53 ` Thomas Gleixner
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