The patch titled
Subject: mm/ksm.c: don't WARN if page is still mapped in remove_stable_node()
has been added to the -mm tree. Its filename is
mm-ksm-dont-warn-if-page-is-still-mapped-in-remove_stable_node.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-ksm-dont-warn-if-page-is-still-mapped-in-remove_stable_node.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-ksm-dont-warn-if-page-is-still-mapped-in-remove_stable_node.patch
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------------------------------------------------------
From: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxx
Fixes: cbf86cfe04a6 ("ksm: remove old stable nodes more thoroughly")
Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/ksm.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
--- a/mm/ksm.c~mm-ksm-dont-warn-if-page-is-still-mapped-in-remove_stable_node
+++ a/mm/ksm.c
@@ -885,13 +885,13 @@ static int remove_stable_node(struct sta
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
_
Patches currently in -mm which might be from aryabinin@xxxxxxxxxxxxx are
mm-ksm-dont-warn-if-page-is-still-mapped-in-remove_stable_node.patch
mm-vmscan-remove-unused-lru_pages-argument.patch
