linux-kernel - [patch] mm, oom: remove 3% bonus for CAP_SYS

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Message-ID: <alpine.DEB.2.20.1803071548510.6996@chino.kir.corp.google.com>
Date:   Wed, 7 Mar 2018 15:52:15 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Gaurav Kohli <gkohli@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>
cc:     mhocko@...e.com, kirill.shutemov@...ux.intel.com,
        Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: [patch] mm, oom: remove 3% bonus for CAP_SYS_ADMIN processes

Since the 2.6 kernel, the oom killer has slightly biased away from 
CAP_SYS_ADMIN processes by discounting some of its memory usage in 
comparison to other processes.

This has always been implicit and nothing exactly relies on the behavior.

Gaurav notices that __task_cred() can dereference a potentially freed 
pointer if the task under consideration is exiting because a reference to 
the task_struct is not held.

Remove the CAP_SYS_ADMIN bias so that all processes are treated equally.

If any CAP_SYS_ADMIN process would like to be biased against, it is always 
allowed to adjust /proc/pid/oom_score_adj.

Reported-by: Gaurav Kohli <gkohli@...eaurora.org>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 mm/oom_kill.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -224,13 +224,6 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
 		mm_pgtables_bytes(p->mm) / PAGE_SIZE;
 	task_unlock(p);

-	/*
-	 * Root processes get 3% bonus, just like the __vm_enough_memory()
-	 * implementation used by LSMs.
-	 */
-	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
-		points -= (points * 3) / 100;
-
 	/* Normalize to oom_score_adj units */
 	adj *= totalpages / 1000;
 	points += adj;