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authorHugh Dickins <hughd@google.com>2021-06-24 18:39:52 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-06-24 19:40:54 -0700
commitfe19bd3dae3d15d2fbfdb3de8839a6ea0fe94264 (patch)
treefab0cfb0af57acaa2ece48ca74d5cf2964b10862 /kernel
parent5fa54346caf67b4b1b10b1f390316ae466da4d53 (diff)
mm, futex: fix shared futex pgoff on shmem huge page
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. [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: 800d8c63b2e9 ("shmem: add huge pages support") Reported-by: Neel Natu <neelnatu@google.com> Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Acked-by: Thomas 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/futex.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 4938a00bc785..408cad5e8968 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -35,7 +35,6 @@
#include <linux/jhash.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
-#include <linux/hugetlb.h>
#include <linux/freezer.h>
#include <linux/memblock.h>
#include <linux/fault-inject.h>
@@ -650,7 +649,7 @@ again:
key->both.offset |= FUT_OFF_INODE; /* inode-based key */
key->shared.i_seq = get_inode_sequence_number(inode);
- key->shared.pgoff = basepage_index(tail);
+ key->shared.pgoff = page_to_pgoff(tail);
rcu_read_unlock();
}