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Subject: Re: [patch] mm, oom: dump stack of victim when reaping failed
To:     Michal Hocko <mhocko@kernel.org>,
        David Rientjes <rientjes@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <alpine.DEB.2.21.2001141519280.200484@chino.kir.corp.google.com>
 <20200115084336.GW19428@dhcp22.suse.cz>
From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Message-ID: <9a7cbbf0-4283-f932-e422-84b4fb42a055@I-love.SAKURA.ne.jp>
Date:   Wed, 15 Jan 2020 18:18:25 +0900
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On 2020/01/15 17:43, Michal Hocko wrote:
> On Tue 14-01-20 15:20:04, David Rientjes wrote:
>> When a process cannot be oom reaped, for whatever reason, currently the
>> list of locks that are held is currently dumped to the kernel log.
>>
>> Much more interesting is the stack trace of the victim that cannot be
>> reaped.  If the stack trace is dumped, we have the ability to find
>> related occurrences in the same kernel code and hopefully solve the
>> issue that is making it wedged.
>>
>> Dump the stack trace when a process fails to be oom reaped.
> 
> Yes, this is really helpful.

tsk would be a thread group leader, but the thread which got stuck is not
always a thread group leader. Maybe dump all threads in that thread group
without PF_EXITING (or something) ?

> 
>> Signed-off-by: David Rientjes <rientjes@google.com>
> 
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
> Thanks!
> 
>> ---
>>  mm/oom_kill.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
>> --- a/mm/oom_kill.c
>> +++ b/mm/oom_kill.c
>> @@ -26,6 +26,7 @@
>>  #include <linux/sched/mm.h>
>>  #include <linux/sched/coredump.h>
>>  #include <linux/sched/task.h>
>> +#include <linux/sched/debug.h>
>>  #include <linux/swap.h>
>>  #include <linux/timex.h>
>>  #include <linux/jiffies.h>
>> @@ -620,6 +621,7 @@ static void oom_reap_task(struct task_struct *tsk)
>>  
>>  	pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
>>  		task_pid_nr(tsk), tsk->comm);
>> +	sched_show_task(tsk);
>>  	debug_show_all_locks();
>>  
>>  done:
>