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

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Message-Id: <201510022133.IJB87676.OOOHFFMtVFSQJL@I-love.SAKURA.ne.jp>
Date:	Fri, 2 Oct 2015 21:33:08 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mhocko@...nel.org
Cc:	oleg@...hat.com, akpm@...ux-foundation.org, rientjes@...gle.com,
	kwalker@...hat.com, skozina@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm v2 1/3] mm/oom_kill: remove the wrong fatal_signal_pending() check in oom_kill_process()

Michal Hocko wrote:
> > Since T sends SIGKILL to all clone(CLONE_VM) tasks upon coredump, P needs
> > to do
> 
> It does that only to all threads in the _same_ thread group AFAIU.

I'm confused. What the _same_ thread group?

I can observe that SIGKILL is sent to all

  clone(CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)
  clone(CLONE_SIGHAND | CLONE_VM)
  clone(CLONE_VM)

threads upon coredump.

---------- testing program start ----------
#define _GNU_SOURCE
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <sched.h>
#include <sys/mman.h>

static int file_mapper(void *unused)
{
        const int fd = open("/proc/self/exe", O_RDONLY);
        void *ptr[10000]; /* Will cause SIGSEGV due to stack overflow */
        int i;
        sleep(2);
        while (1) {
                for (i = 0; i < 10000; i++)
                        ptr[i] = mmap(NULL, 4096, PROT_READ, MAP_PRIVATE, fd,
                                      0);
                for (i = 0; i < 10000; i++)
                        munmap(ptr[i], 4096);
        }
        return 0;
}

int main(int argc, char *argv[])
{
        int i;
        for (i = 0; i < 5; i++) {
                char *cp = malloc(4 * 1024);
                if (!cp || clone(file_mapper, cp + 4 * 1024,
                                 CLONE_THREAD | CLONE_SIGHAND | CLONE_VM, NULL) == -1)
                        break;
        }
        for (i = 0; i < 5; i++) {
                char *cp = malloc(4 * 1024);
                if (!cp || clone(file_mapper, cp + 4 * 1024,
                                 CLONE_SIGHAND | CLONE_VM, NULL) == -1)
                        break;
        }
        for (i = 0; i < 5; i++) {
                char *cp = malloc(4 * 1024);
                if (!cp || clone(file_mapper, cp + 4 * 1024,
                                 CLONE_VM, NULL) == -1)
                        break;
        }
        while (1)
                pause();
        return 0;
}
---------- testing program end ----------

---------- debug printk() patch start ----------
--- 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 ----------

---------- kernel log start ----------
[ 4829.770899] a.out[11614]: segfault at 1e1f768 ip 00000000004007be sp 0000000001e1f770 error 6 in a.out[400000+1000]
[ 4829.774190] Setting SIGKILL to a.out(11613)
[ 4829.775954] Setting SIGKILL to a.out(11615)
[ 4829.777191] Setting SIGKILL to a.out(11616)
[ 4829.778381] Setting SIGKILL to a.out(11617)
[ 4829.779537] Setting SIGKILL to a.out(11618)
[ 4829.781057] Setting SIGKILL to a.out(11619)
[ 4829.782236] Setting SIGKILL to a.out(11620)
[ 4829.783401] Setting SIGKILL to a.out(11621)
[ 4829.784569] Setting SIGKILL to a.out(11622)
[ 4829.785700] Setting SIGKILL to a.out(11623)
[ 4829.786848] Setting SIGKILL to a.out(11624)
[ 4829.788001] Setting SIGKILL to a.out(11625)
[ 4829.789132] Setting SIGKILL to a.out(11626)
[ 4829.790332] Setting SIGKILL to a.out(11627)
[ 4829.791593] Setting SIGKILL to a.out(11628)
[ 4829.792941] a.out[11624]: segfault at 1e29808 ip 00000000004007be sp 0000000001e29810 error 6 in a.out[400000+1000]
[ 4829.795493] a.out[11622]: segfault at 1e277e8 ip 00000000004007be sp 0000000001e277f0 error 6
[ 4829.797171] a.out[11623]: segfault at 1e287f8 ip 00000000004007be sp 0000000001e28800 error 6
[ 4829.797545] a.out[11621]: segfault at 1e267d8 ip 00000000004007be sp 0000000001e267e0 error 6
[ 4829.797547] a.out[11618]: segfault at 1e237a8 ip 00000000004007be sp 0000000001e237b0 error 6
[ 4829.797548] a.out[11617]: segfault at 1e22798 ip 00000000004007be sp 0000000001e227a0 error 6
[ 4829.797550] a.out[11619]: segfault at 1e247b8 ip 00000000004007be sp 0000000001e247c0 error 6
[ 4829.797552] a.out[11620]: segfault at 1e257c8 ip 00000000004007be sp 0000000001e257d0 error 6
[ 4829.802631] a.out[11615]: segfault at 1e20778 ip 00000000004007be sp 0000000001e20780 error 6
[ 4829.802633]  in a.out[400000+1000]
[ 4829.802639]  in a.out[400000+1000]
[ 4829.802642]  in a.out[400000+1000]
[ 4829.802655]  in a.out[400000+1000]
[ 4829.802659]  in a.out[400000+1000]
[ 4829.802662]  in a.out[400000+1000]
[ 4829.814605]  in a.out[400000+1000]
[ 4829.819500]  in a.out[400000+1000]
---------- kernel log end ----------
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