• Hugh Dickins's avatar
    mm, futex: fix shared futex pgoff on shmem huge page · fe19bd3d
    Hugh Dickins authored
    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 13d60f4b ("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.
    
    [akpm@linux-foundation.org: give hugetlb_basepage_index() prototype the correct scope]
    
    Link: https://lkml.kernel.org/r/b17d946b-d09-326e-b42a-52884c36df32@google.com
    Fixes: 800d8c63 ("shmem: add huge pages support")
    Reported-by: default avatarNeel Natu <neelnatu@google.com>
    Signed-off-by: default avatarHugh Dickins <hughd@google.com>
    Reviewed-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
    Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    Cc: Zhang Yi <wetpzy@gmail.com>
    Cc: Mel Gorman <mgorman@techsingularity.net>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Darren Hart <dvhart@infradead.org>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    fe19bd3d
hugetlb.c 167 KB