+ mm-increment-gen-before-restarting-traversal.patch added to mm-unstable branch

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The patch titled
     Subject: mm: increment gen # before restarting traversal
has been added to the -mm mm-unstable branch.  Its filename is
     mm-increment-gen-before-restarting-traversal.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-increment-gen-before-restarting-traversal.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Kinsey Ho <kinseyho@xxxxxxxxxx>
Subject: mm: increment gen # before restarting traversal
Date: Thu, 5 Sep 2024 00:30:52 +0000

The generation number in struct mem_cgroup_reclaim_iter should be
incremented on every round-trip.  Currently, it is possible for a
concurrent reclaimer to jump in at the end of the hierarchy, causing a
traversal restart (resetting the iteration position) without incrementing
the generation number.

By resetting the position without incrementing the generation, it's
possible for another ongoing mem_cgroup_iter() thread to walk the tree
twice.

Move the traversal restart such that the generation number is
incremented before the restart.

Link: https://lkml.kernel.org/r/20240905003058.1859929-4-kinseyho@xxxxxxxxxx
Signed-off-by: Kinsey Ho <kinseyho@xxxxxxxxxx>
Reviewed-by: T.J. Mercier <tjmercier@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michal Koutný <mkoutny@xxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Cc: Zefan Li <lizefan.x@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/memcontrol.c |   22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

--- a/mm/memcontrol.c~mm-increment-gen-before-restarting-traversal
+++ a/mm/memcontrol.c
@@ -999,7 +999,7 @@ struct mem_cgroup *mem_cgroup_iter(struc
 		root = root_mem_cgroup;
 
 	rcu_read_lock();
-
+restart:
 	if (reclaim) {
 		struct mem_cgroup_per_node *mz;
 
@@ -1026,14 +1026,6 @@ struct mem_cgroup *mem_cgroup_iter(struc
 	for (;;) {
 		css = css_next_descendant_pre(css, &root->css);
 		if (!css) {
-			/*
-			 * Reclaimers share the hierarchy walk, and a
-			 * new one might jump in right at the end of
-			 * the hierarchy - make sure they see at least
-			 * one group and restart from the beginning.
-			 */
-			if (!prev)
-				continue;
 			break;
 		}
 
@@ -1056,8 +1048,18 @@ struct mem_cgroup *mem_cgroup_iter(struc
 		 */
 		(void)cmpxchg(&iter->position, pos, memcg);
 
-		if (!memcg)
+		if (!memcg) {
 			iter->generation++;
+
+			/*
+			 * Reclaimers share the hierarchy walk, and a
+			 * new one might jump in right at the end of
+			 * the hierarchy - make sure they see at least
+			 * one group and restart from the beginning.
+			 */
+			if (!prev)
+				goto restart;
+		}
 	}
 
 out_unlock:
_

Patches currently in -mm which might be from kinseyho@xxxxxxxxxx are

cgroup-clarify-css-sibling-linkage-is-protected-by-cgroup_mutex-or-rcu.patch
mm-dont-hold-css-refcnt-during-traversal.patch
mm-increment-gen-before-restarting-traversal.patch
mm-restart-if-multiple-traversals-raced.patch
mm-clean-up-mem_cgroup_iter.patch





[Index of Archives]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]

  Powered by Linux