Re: [BUG] sched: leaf_cfs_rq_list use after free

[Kazuki Yamaguchi <k@rhe.jp>]

Hello,

I got similar kernel crashes after the patch, which went to 4.4:

2e91fa7 cgroup: keep zombies associated with their original cgroups

I was just about to report, but maybe this is related?

^^^^^^^[    0.761718] BUG: unable to handle kernel NULL pointer 
dereference at 00000000000008b0
[    0.762860] IP: [<ffffffff81052630>] update_blocked_averages+0x80/0x600
[    0.764020] PGD 3fc067 PUD 3a9067 PMD 0
[    0.764020] Oops: 0000 [#1] SMP
[    0.764020] CPU: 0 PID: 56 Comm: test Not tainted 4.5.0-rc7 #25
[    0.764020] task: ffff8800003d2700 ti: ffff8800003e8000 task.ti: 
ffff8800003e8000
[    0.764020] RIP: 0010:[<ffffffff81052630>]  [<ffffffff81052630>] 
update_blocked_averages+0x80/0x600
[    0.764020] RSP: 0000:ffff880007c03e50  EFLAGS: 00000016
[    0.764020] RAX: 0000000000000000 RBX: 00000000ffff165e RCX: 
000000002d5096e1
[    0.764020] RDX: 00000000000d281c RSI: ffff880000138200 RDI: 
00000000000d281c
[    0.764020] RBP: ffff880007c03eb0 R08: ffffffff811567e0 R09: 
0000000000000100
[    0.764020] R10: 0000000000000000 R11: 0000000000000000 R12: 
ffff880007c11920
[    0.764020] R13: 00000000000110c0 R14: afb504000afb5041 R15: 
ffff880007c110c0
[    0.764020] FS:  0000000001b69880(0063) GS:ffff880007c00000(0000) 
knlGS:0000000000000000
[    0.764020] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[    0.764020] CR2: 00000000000008b0 CR3: 00000000003a4000 CR4: 
00000000000006b0
[    0.764020] Stack:
[    0.764020]  0000000080000100 0000000000000286 ffff880007c0c7f8 
0000000000000006
[    0.764020]  0000000007c0c5c0 ffff880000138200 ffffffff8104ce00 
00000000ffff165e
[    0.764020]  ffff880007c110c0 00000000000110c0 0000000000000007 
0000000000000000
[    0.764020] Call Trace:
[    0.764020]  <IRQ>
[    0.764020]  [<ffffffff8104ce00>] ? wake_up_process+0x10/0x20
[    0.764020]  [<ffffffff8105978d>] run_rebalance_domains+0x6d/0x290
[    0.764020]  [<ffffffff81072cab>] ? run_timer_softirq+0x19b/0x220
[    0.764020]  [<ffffffff810318ee>] __do_softirq+0xde/0x1e0
[    0.764020]  [<ffffffff81031aef>] irq_exit+0x5f/0x70
[    0.764020]  [<ffffffff81020238>] 
smp_trace_apic_timer_interrupt+0x68/0x90
[    0.764020]  [<ffffffff81020269>] smp_apic_timer_interrupt+0x9/0x10
[    0.764020]  [<ffffffff8114dd4c>] apic_timer_interrupt+0x7c/0x90
[    0.764020]  <EOI>
[    0.764020]  [<ffffffff810b76f6>] ? find_vma+0x16/0x70
[    0.764020]  [<ffffffff81026d18>] __do_page_fault+0xe8/0x360
[    0.764020]  [<ffffffff81026fcc>] do_page_fault+0xc/0x10
[    0.764020]  [<ffffffff8114e5cf>] page_fault+0x1f/0x30
[    0.764020] Code: 00 48 8d b0 28 ff ff ff 49 be 41 50 fb 0a 00 04 b5 
af 48 89 74 24 28 48 8b 74 24 28 c7 44 24 24 00 00 00 00 48 8b 86 c8 00 
00 00 <48> 8b 90 b0 08 00 00 48 8b 86 a0 00 00 00 48 85 c0 74 46 31 c0
[    0.764020] RIP  [<ffffffff81052630>] update_blocked_averages+0x80/0x600
[    0.764020]  RSP <ffff880007c03e50>
[    0.764020] CR2: 00000000000008b0
[    0.764020] ---[ end trace 754fbc727003a126 ]---
[    0.764020] Kernel panic - not syncing: Fatal exception in interrupt
[    0.764020] Shutting down cpus with NMI
[    0.764020] Kernel Offset: disabled
[    0.764020] ---[ end Kernel panic - not syncing: Fatal exception in 
interrupt


I can reproduce it on QEMU (qemu-system-x86_64 -smp 2).

enabled config:
CONFIG_PID_NS=y
CONFIG_FAIR_GROUP_SCHED=y
CONFIG_SMP=y


init.sh:
#!/bin/sh
mkdir /testg
mount -t cgroup -o cpu cgroup /testg
echo /agent.sh > /testg/release_agent
echo 1 > /testg/notify_on_release

mkdir /temp-mnt
while :; do
    echo -n ^
    ./test
done


agent.sh:
#!/bin/sh
rmdir /testg$1


test.c:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sched.h>
#include <sys/wait.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/ptrace.h>

int
main(void)
{
     mount("none", "/temp-mnt", "tmpfs", 0, "");
     unshare(CLONE_NEWPID);
     pid_t pid = fork();
     if (pid == 0) {
         fork();
     } else {
         ptrace(PTRACE_SEIZE, pid, 0, PTRACE_O_TRACEFORK);
         char template[128] = "/testg/XXXXXX";
         if (!mkdtemp(template)) abort();
         FILE *f = fopen(strcat(template, "/cgroup.procs"), "w");
         fprintf(f, "%d\n", pid);
         fclose(f);
         wait(NULL); // stopped at fork()
         kill(pid, SIGKILL);
         umount("/temp-mnt");
     }
     return 0;
}

-- 
Kazuki Yamaguchi <k@rhe.jp>