From: Michal Hocko <mhocko@xxxxxxxx>
Subject: proc, oom: do not report alien mms when setting oom_score_adj
Tetsuo has reported that creating a thousands of processes sharing MM
without SIGHAND (aka alien threads) and setting /proc/<pid>/oom_score_adj
will swamp the kernel log and takes ages [1] to finish. This is
especially worrisome that all that printing is done under RCU lock and
this can potentially trigger RCU stall or softlockup detector.
The primary reason for the printk was to catch potential users who might
depend on the behavior prior to 44a70adec910 ("mm, oom_adj: make sure
processes sharing mm have same view of oom_score_adj") but after more than
2 years without a single report I guess it is safe to simply remove the
printk altogether.
The next step should be moving oom_score_adj over to the mm struct and
remove all the tasks crawling as suggested by [2]
[1] http://lkml.kernel.org/r/97fce864-6f75-bca5-14bc-12c9f890e740@xxxxxxxxxxxxxxxxxxx
[2] http://lkml.kernel.org/r/20190117155159.GA4087@xxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20190212102129.26288-1-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Yong-Taek Lee <ytk.lee@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/fs/proc/base.c~proc-oom-do-not-report-alien-mms-when-setting-oom_score_adj
+++ a/fs/proc/base.c
@@ -1086,10 +1086,6 @@ static int __set_oom_adj(struct file *fi
task_lock(p);
if (!p->vfork_done && process_shares_mm(p, mm)) {
- pr_info("updating oom_score_adj for %d (%s) from %d to %d because it shares mm with %d (%s). Report if this is unexpected.\n",
- task_pid_nr(p), p->comm,
- p->signal->oom_score_adj, oom_adj,
- task_pid_nr(task), task->comm);
p->signal->oom_score_adj = oom_adj;
if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE))
p->signal->oom_score_adj_min = (short)oom_adj;
_
