From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxxxxxx: give hugetlb_basepage_index() prototype the correct scope]
Link: https://lkml.kernel.org/r/b17d946b-d09-326e-b42a-52884c36df32@xxxxxxxxxx
Fixes: 800d8c63b2e9 ("shmem: add huge pages support")
Reported-by: Neel Natu <neelnatu@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Zhang Yi <wetpzy@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Darren Hart <dvhart@xxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/hugetlb.h | 16 ----------------
include/linux/pagemap.h | 13 +++++++------
kernel/futex.c | 3 +--
mm/hugetlb.c | 5 +----
4 files changed, 9 insertions(+), 28 deletions(-)
--- a/include/linux/hugetlb.h~mm-futex-fix-shared-futex-pgoff-on-shmem-huge-page
+++ a/include/linux/hugetlb.h
@@ -741,17 +741,6 @@ static inline int hstate_index(struct hs
return h - hstates;
}
-pgoff_t __basepage_index(struct page *page);
-
-/* Return page->index in PAGE_SIZE units */
-static inline pgoff_t basepage_index(struct page *page)
-{
- if (!PageCompound(page))
- return page->index;
-
- return __basepage_index(page);
-}
-
extern int dissolve_free_huge_page(struct page *page);
extern int dissolve_free_huge_pages(unsigned long start_pfn,
unsigned long end_pfn);
@@ -988,11 +977,6 @@ static inline int hstate_index(struct hs
return 0;
}
-static inline pgoff_t basepage_index(struct page *page)
-{
- return page->index;
-}
-
static inline int dissolve_free_huge_page(struct page *page)
{
return 0;
--- a/include/linux/pagemap.h~mm-futex-fix-shared-futex-pgoff-on-shmem-huge-page
+++ a/include/linux/pagemap.h
@@ -516,7 +516,7 @@ static inline struct page *read_mapping_
}
/*
- * Get index of the page with in radix-tree
+ * Get index of the page within radix-tree (but not for hugetlb pages).
* (TODO: remove once hugetlb pages will have ->index in PAGE_SIZE)
*/
static inline pgoff_t page_to_index(struct page *page)
@@ -535,15 +535,16 @@ static inline pgoff_t page_to_index(stru
return pgoff;
}
+extern pgoff_t hugetlb_basepage_index(struct page *page);
+
/*
- * Get the offset in PAGE_SIZE.
- * (TODO: hugepage should have ->index in PAGE_SIZE)
+ * Get the offset in PAGE_SIZE (even for hugetlb pages).
+ * (TODO: hugetlb pages should have ->index in PAGE_SIZE)
*/
static inline pgoff_t page_to_pgoff(struct page *page)
{
- if (unlikely(PageHeadHuge(page)))
- return page->index << compound_order(page);
-
+ if (unlikely(PageHuge(page)))
+ return hugetlb_basepage_index(page);
return page_to_index(page);
}
--- a/kernel/futex.c~mm-futex-fix-shared-futex-pgoff-on-shmem-huge-page
+++ a/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();
}
--- a/mm/hugetlb.c~mm-futex-fix-shared-futex-pgoff-on-shmem-huge-page
+++ a/mm/hugetlb.c
@@ -1588,15 +1588,12 @@ struct address_space *hugetlb_page_mappi
return NULL;
}
-pgoff_t __basepage_index(struct page *page)
+pgoff_t hugetlb_basepage_index(struct page *page)
{
struct page *page_head = compound_head(page);
pgoff_t index = page_index(page_head);
unsigned long compound_idx;
- if (!PageHuge(page_head))
- return page_index(page);
-
if (compound_order(page_head) >= MAX_ORDER)
compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
else
_
