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 44a70ade ("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.ne.jp [2] http://lkml.kernel.org/r/20190117155159.GA4087@dhcp22.suse.cz Link: http://lkml.kernel.org/r/20190212102129.26288-1-mhocko@kernel.orgSigned-off-by: NMichal Hocko <mhocko@suse.com> Reported-by: NTetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> Acked-by: NJohannes 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: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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