FAILED: patch "[PATCH] mm: treat indirectly reclaimable memory as free in overcommit" failed to apply to 4.16-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.16-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From d79f7aa496fc94d763f67b833a1f36f4c171176f Mon Sep 17 00:00:00 2001
From: Roman Gushchin <guro@fb.com>
Date: Tue, 10 Apr 2018 16:27:47 -0700
Subject: [PATCH] mm: treat indirectly reclaimable memory as free in overcommit
 logic

Indirectly reclaimable memory can consume a significant part of total
memory and it's actually reclaimable (it will be released under actual
memory pressure).

So, the overcommit logic should treat it as free.

Otherwise, it's possible to cause random system-wide memory allocation
failures by consuming a significant amount of memory by indirectly
reclaimable memory, e.g.  dentry external names.

If overcommit policy GUESS is used, it might be used for denial of
service attack under some conditions.

The following program illustrates the approach.  It causes the kernel to
allocate an unreclaimable kmalloc-256 chunk for each stat() call, so
that at some point the overcommit logic may start blocking large
allocation system-wide.

  int main()
  {
  	char buf[256];
  	unsigned long i;
  	struct stat statbuf;

  	buf[0] = '/';
  	for (i = 1; i < sizeof(buf); i++)
  		buf[i] = '_';

  	for (i = 0; 1; i++) {
  		sprintf(&buf[248], "%8lu", i);
  		stat(buf, &statbuf);
  	}

  	return 0;
  }

This patch in combination with related indirectly reclaimable memory
patches closes this issue.

Link: http://lkml.kernel.org/r/20180313130041.8078-1-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/util.c b/mm/util.c
index 029fc2f3b395..73676f0f1b43 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -667,6 +667,13 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 		 */
 		free += global_node_page_state(NR_SLAB_RECLAIMABLE);
 
+		/*
+		 * Part of the kernel memory, which can be released
+		 * under memory pressure.
+		 */
+		free += global_node_page_state(
+			NR_INDIRECTLY_RECLAIMABLE_BYTES) >> PAGE_SHIFT;
+
 		/*
 		 * Leave reserved pages. The pages are not for anonymous pages.
 		 */