From: Michal Hocko mhocko@suse.com 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@i-love.sakura.... [2] http://lkml.kernel.org/r/20190117155159.GA4087@dhcp22.suse.cz

Link: http://lkml.kernel.org/r/20190212102129.26288-1-mhocko@kernel.org Signed-off-by: Michal Hocko mhocko@suse.com Reported-by: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Acked-by: Johannes Weiner hannes@cmpxchg.org Cc: David Rientjes rientjes@google.com Cc: Yong-Taek Lee ytk.lee@samsung.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

--- 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; _