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authorAndrey Ryabinin <aryabinin@virtuozzo.com>2019-11-22 04:54:01 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2019-11-22 20:11:18 +0300
commit9a63236f1ad82d71a98aa80320b6cb618fb32f44 (patch)
tree84ff12b4f2967d245c12cf03abfb9f84e9680da1
parent7ce700bf11b5e2cb84e4352bbdf2123a7a239c84 (diff)
downloadlinux-9a63236f1ad82d71a98aa80320b6cb618fb32f44.tar.xz
mm/ksm.c: don't WARN if page is still mapped in remove_stable_node()
It's possible to hit the WARN_ON_ONCE(page_mapped(page)) in remove_stable_node() when it races with __mmput() and squeezes in between ksm_exit() and exit_mmap(). WARNING: CPU: 0 PID: 3295 at mm/ksm.c:888 remove_stable_node+0x10c/0x150 Call Trace: remove_all_stable_nodes+0x12b/0x330 run_store+0x4ef/0x7b0 kernfs_fop_write+0x200/0x420 vfs_write+0x154/0x450 ksys_write+0xf9/0x1d0 do_syscall_64+0x99/0x510 entry_SYSCALL_64_after_hwframe+0x49/0xbe Remove the warning as there is nothing scary going on. Link: http://lkml.kernel.org/r/20191119131850.5675-1-aryabinin@virtuozzo.com Fixes: cbf86cfe04a6 ("ksm: remove old stable nodes more thoroughly") Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Acked-by: Hugh Dickins <hughd@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/ksm.c14
1 files changed, 7 insertions, 7 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index dbee2eb4dd05..7905934cd3ad 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -885,13 +885,13 @@ static int remove_stable_node(struct stable_node *stable_node)
return 0;
}
- if (WARN_ON_ONCE(page_mapped(page))) {
- /*
- * This should not happen: but if it does, just refuse to let
- * merge_across_nodes be switched - there is no need to panic.
- */
- err = -EBUSY;
- } else {
+ /*
+ * Page could be still mapped if this races with __mmput() running in
+ * between ksm_exit() and exit_mmap(). Just refuse to let
+ * merge_across_nodes/max_page_sharing be switched.
+ */
+ err = -EBUSY;
+ if (!page_mapped(page)) {
/*
* The stable node did not yet appear stale to get_ksm_page(),
* since that allows for an unmapped ksm page to be recognized