[Devel] [PATCH RHEL7 COMMIT] ms/memcg: prohibit unconditional exceeding the limit of dying tasks

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.41.1.vz7.183.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.41.1.vz7.183.3
------>
commit 30b7acd04f1384f4a69b98805b943bb868d1e420
Author: Vasily Averin <vvs at virtuozzo.com>
Date:   Tue Sep 14 09:57:01 2021 +0300

    ms/memcg: prohibit unconditional exceeding the limit of dying tasks
    
    The kernel currently allows dying tasks to exceed the memcg limits.
    The allocation is expected to be the last one and the occupied memory
    will be freed soon.
    This is not always true because it can be part of the huge vmalloc
    allocation. Allowed once, they will repeat over and over again.
    Moreover lifetime of the allocated object can differ from
    In addition the lifetime of the dying task.
    Multiple such allocations running concurrently can not only overuse
    the memcg limit, but can lead to a global out of memory and,
    in the worst case, cause the host to panic.
    
    [backport of upstream patch version]
    Link: https://lkml.org/lkml/2021/9/10/374
    https://jira.sw.ru/browse/PSBM-132705
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 mm/memcontrol.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b48c84b..4c3cc09 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3347,17 +3347,6 @@ retry:
 	}
 
 	/*
-	 * Unlike in global OOM situations, memcg is not in a physical
-	 * memory shortage.  Allow dying and OOM-killed tasks to
-	 * bypass the last charges so that they can exit quickly and
-	 * free their memory.
-	 */
-	if (unlikely(test_thread_flag(TIF_MEMDIE) ||
-		     fatal_signal_pending(current) ||
-		     current->flags & PF_EXITING))
-		goto bypass;
-
-	/*
 	 * Prevent unbounded recursion when reclaim operations need to
 	 * allocate memory. This might exceed the limits temporarily,
 	 * but we prefer facilitating memory reclaim and getting back
@@ -3411,9 +3400,6 @@ retry:
 	if (gfp_mask & __GFP_NOFAIL)
 		goto bypass;
 
-	if (fatal_signal_pending(current))
-		goto bypass;
-
 	/*
 	 * We might have [a lot of] reclaimable kmem which we cannot reclaim in
 	 * the current context, e.g. lot of inodes/dentries while tring to get