another patch

2 files changed, 64 insertions, 0 deletions

diff --git a/mm-ksm.c-don-t-warn-if-page-is-still-mapped-in-remove_stable_node.patch b/mm-ksm.c-don-t-warn-if-page-is-still-mapped-in-remove_stable_node.patch
new file mode 100644
index 0000000..debe954
--- /dev/null
+++ b/mm-ksm.c-don-t-warn-if-page-is-still-mapped-in-remove_stable_node.patch
@@ -0,0 +1,63 @@
+From 9a63236f1ad82d71a98aa80320b6cb618fb32f44 Mon Sep 17 00:00:00 2001
+From: Andrey Ryabinin <aryabinin@virtuozzo.com>
+Date: Thu, 21 Nov 2019 17:54:01 -0800
+Subject: mm/ksm.c: don't WARN if page is still mapped in remove_stable_node()
+
+From: Andrey Ryabinin <aryabinin@virtuozzo.com>
+
+commit 9a63236f1ad82d71a98aa80320b6cb618fb32f44 upstream.
+
+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>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ mm/ksm.c |   14 +++++++-------
+ 1 file changed, 7 insertions(+), 7 deletions(-)
+
+--- a/mm/ksm.c
++++ b/mm/ksm.c
+@@ -713,13 +713,13 @@ 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
diff --git a/series b/series
index b6f1939..c0bab30 100644
--- a/series
+++ b/series
@@ -2,3 +2,4 @@ net-mlx4_en-fix-mlx4-ethtool-n-insertion.patch
 sfc-only-cancel-the-pps-workqueue-if-it-exists.patch
 net-sched-act_pedit-fix-warn-in-the-traffic-path.patch
 net-rtnetlink-prevent-underflows-in-do_setvfinfo.patch
+mm-ksm.c-don-t-warn-if-page-is-still-mapped-in-remove_stable_node.patch