Re: [PATCH -mm v2 1/3] mm/oom_kill: remove the wrong fatal_signal_pending() check in oom_kill_process()

[Tetsuo Handa]

Michal Hocko wrote:
> > --- a/fs/coredump.c
> > +++ b/fs/coredump.c
> > @@ -295,6 +295,8 @@ static int zap_process(struct task_struct *start, int exit_code, int flags)
> >         for_each_thread(start, t) {
> >                 task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
> >                 if (t != current && t->mm) {
> > +                       printk(KERN_INFO "Setting SIGKILL to %s(%u)\n",
> > +                              t->comm, t->pid);
> >                         sigaddset(&t->pending.signal, SIGKILL);
> >                         signal_wake_up(t, 1);
> >                         nr++;
> > ---------- debug printk() patch end ----------
> 
> OK, but all your tasks should trigger SEGV. You cannot find out whether
> all of them happened from the same zap_process, can you.

Indeed. I retested with updated patch. Not all of them are killed from
the same zap_process, but all of them are killed by the same SEGV event.
I think that coredump stops all threads sharing the same memory.

---------- debug printk() patch start ----------
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -292,14 +292,18 @@ static int zap_process(struct task_struct *start, int exit_code, int flags)
        start->signal->group_exit_code = exit_code;
        start->signal->group_stop_count = 0;

+       printk(KERN_INFO "%s(%d): Started zap_process()\n", current->comm, current->pid);
        for_each_thread(start, t) {
                task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
                if (t != current && t->mm) {
+                       printk(KERN_INFO "%s(%d): Setting SIGKILL to %s(%u)\n",
+                              current->comm, current->pid, t->comm, t->pid);
                        sigaddset(&t->pending.signal, SIGKILL);
                        signal_wake_up(t, 1);
                        nr++;
                }
        }
+       printk(KERN_INFO "%s(%d): zap_process() returned %d\n", current->comm, current->pid, nr);

        return nr;
 }
---------- debug printk() patch end ----------

---------- kernel log start ----------
[   71.808316] a.out[11057]: segfault at 7ac768 ip 00000000004007be sp 00000000007ac770 error 6 in a.out[400000+1000]
[   71.811003] a.out[11058]: segfault at 7ad778 ip 00000000004007be sp 00000000007ad780 error 6
[   71.811005]  in a.out[400000+1000]
[   71.813817] a.out(11058): Started zap_process()
[   71.813818] a.out(11058): Setting SIGKILL to a.out(11056)
[   71.813841] a.out(11058): Setting SIGKILL to a.out(11057)
[   71.813854] a.out(11058): Setting SIGKILL to a.out(11059)
[   71.813855] a.out(11058): Setting SIGKILL to a.out(11060)
[   71.813855] a.out(11058): Setting SIGKILL to a.out(11061)
[   71.813857] a.out(11058): zap_process() returned 5
[   71.813880] a.out(11058): Started zap_process()
[   71.813880] a.out(11058): Setting SIGKILL to a.out(11062)
[   71.813881] a.out(11058): zap_process() returned 1
[   71.813881] a.out(11058): Started zap_process()
[   71.813882] a.out(11058): Setting SIGKILL to a.out(11063)
[   71.813882] a.out(11058): zap_process() returned 1
[   71.813882] a.out(11058): Started zap_process()
[   71.813883] a.out(11058): Setting SIGKILL to a.out(11064)
[   71.813883] a.out(11058): zap_process() returned 1
[   71.813884] a.out(11058): Started zap_process()
[   71.813884] a.out(11058): Setting SIGKILL to a.out(11065)
[   71.813899] a.out(11058): zap_process() returned 1
[   71.813900] a.out(11058): Started zap_process()
[   71.813900] a.out(11058): Setting SIGKILL to a.out(11066)
[   71.813901] a.out(11058): zap_process() returned 1
[   71.813901] a.out(11058): Started zap_process()
[   71.813902] a.out(11058): Setting SIGKILL to a.out(11067)
[   71.813902] a.out(11058): zap_process() returned 1
[   71.813903] a.out(11058): Started zap_process()
[   71.813904] a.out(11058): Setting SIGKILL to a.out(11068)
[   71.813904] a.out(11058): zap_process() returned 1
[   71.813905] a.out(11058): Started zap_process()
[   71.813905] a.out(11058): Setting SIGKILL to a.out(11069)
[   71.813906] a.out(11058): zap_process() returned 1
[   71.813906] a.out(11058): Started zap_process()
[   71.813907] a.out(11058): Setting SIGKILL to a.out(11070)
[   71.813907] a.out(11058): zap_process() returned 1
[   71.813908] a.out(11058): Started zap_process()
[   71.813908] a.out(11058): Setting SIGKILL to a.out(11071)
[   71.813908] a.out(11058): zap_process() returned 1
[   71.813925] a.out[11068]: segfault at 7b7818 ip 00000000004007be sp 00000000007b7820 error 6 in a.out[400000+1000]
[   71.813938] a.out[11063]: segfault at 7b27c8 ip 00000000004007be sp 00000000007b27d0 error 6
[   71.813940] a.out[11064]: segfault at 7b37d8 ip 00000000004007be sp 00000000007b37e0 error 6
[   71.813941] a.out[11066]: segfault at 7b57f8 ip 00000000004007be sp 00000000007b5800 error 6
[   71.813943] a.out[11060]: segfault at 7af798 ip 00000000004007be sp 00000000007af7a0 error 6
[   71.813945] a.out[11062]: segfault at 7b17b8 ip 00000000004007be sp 00000000007b17c0 error 6
[   71.813946] a.out[11067]: segfault at 7b6808 ip 00000000004007be sp 00000000007b6810 error 6
[   71.813994] a.out[11070]: segfault at 7b9838 ip 00000000004007be sp 00000000007b9840 error 6
[   71.813995]  in a.out[400000+1000]
[   71.813998]  in a.out[400000+1000]
[   71.814002]  in a.out[400000+1000]
[   71.814004]  in a.out[400000+1000]
[   71.814008]  in a.out[400000+1000]
[   71.814011]  in a.out[400000+1000]
[   71.814015]  in a.out[400000+1000]
---------- kernel log end ----------
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