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authorArnd Bergmann <arnd@arndb.de>2012-01-09 16:06:31 +0000
committerArnd Bergmann <arnd@arndb.de>2012-01-09 16:06:31 +0000
commitb48741cce3be32a48af9a2b272f3f13a077375cf (patch)
treee4bc91713e02fa6d8f08b07de53ea8f905593dfa /kernel/futex.c
parent54b6c82ac9a124804816f244f587c0f40d25ad01 (diff)
parenta07613a54d700a974f3a4a657da78ef5d097315d (diff)
Merge branch 'samsung/cleanup' into next/cleanup2
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c28
1 files changed, 20 insertions, 8 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index ea87f4d2f45..1614be20173 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -314,17 +314,29 @@ again:
#endif
lock_page(page_head);
+
+ /*
+ * If page_head->mapping is NULL, then it cannot be a PageAnon
+ * page; but it might be the ZERO_PAGE or in the gate area or
+ * in a special mapping (all cases which we are happy to fail);
+ * or it may have been a good file page when get_user_pages_fast
+ * found it, but truncated or holepunched or subjected to
+ * invalidate_complete_page2 before we got the page lock (also
+ * cases which we are happy to fail). And we hold a reference,
+ * so refcount care in invalidate_complete_page's remove_mapping
+ * prevents drop_caches from setting mapping to NULL beneath us.
+ *
+ * The case we do have to guard against is when memory pressure made
+ * shmem_writepage move it from filecache to swapcache beneath us:
+ * an unlikely race, but we do need to retry for page_head->mapping.
+ */
if (!page_head->mapping) {
+ int shmem_swizzled = PageSwapCache(page_head);
unlock_page(page_head);
put_page(page_head);
- /*
- * ZERO_PAGE pages don't have a mapping. Avoid a busy loop
- * trying to find one. RW mapping would have COW'd (and thus
- * have a mapping) so this page is RO and won't ever change.
- */
- if ((page_head == ZERO_PAGE(address)))
- return -EFAULT;
- goto again;
+ if (shmem_swizzled)
+ goto again;
+ return -EFAULT;
}
/*