Date:	Wed, 25 Nov 2015 00:59:52 +0200
From:	Andrew <nitr0@...i.kr.ua>
To:	Alexander Duyck <alexander.duyck@...il.com>, netdev@...r.kernel.org
Subject: Re: Kernel 4.1.12 crash

Hi.

I tried to reproduce errors in virtual environment (some VMs on my 
notebook).

I've tried to create 1000 client PPPoE sessions from this box via script:
for i in `seq 1 1000`; do pppd plugin rp-pppoe.so user test password 
test nodefaultroute maxfail 0 persist nodefaultroute holdoff 1 noauth 
eth0; done

And on VM that is used as client I've got strange random crashes (that 
are present only when server is online - so they're network-related):

http://postimg.org/image/ohr2mu3rj/ - crash is here:
(gdb) list *process_one_work+0x32
0xc10607b2 is in process_one_work 
(/var/testpoint/LEAF/source/i486-unknown-linux-uclibc/linux/linux-4.1/kernel/workqueue.c:1952).
1947    __releases(&pool->lock)
1948    __acquires(&pool->lock)
1949    {
1950        struct pool_workqueue *pwq = get_work_pwq(work);
1951        struct worker_pool *pool = worker->pool;
1952        bool cpu_intensive = pwq->wq->flags & WQ_CPU_INTENSIVE;
1953        int work_color;
1954        struct worker *collision;
1955    #ifdef CONFIG_LOCKDEP
1956        /*


http://postimg.org/image/x9mychssx/ - crash is here (noticed twice):
0xc10658bf is in kthread_data 
(/var/testpoint/LEAF/source/i486-unknown-linux-uclibc/linux/linux-4.1/kernel/kthread.c:136).
131     * The caller is responsible for ensuring the validity of @task when
132     * calling this function.
133     */
134    void *kthread_data(struct task_struct *task)
135    {
136        return to_kthread(task)->data;
137    }

which is leaded by strange place:
(gdb) list *kthread_create_on_node+0x120
0xc1065340 is in kthread 
(/var/testpoint/LEAF/source/i486-unknown-linux-uclibc/linux/linux-4.1/kernel/kthread.c:176).
171    {
172        __kthread_parkme(to_kthread(current));
173    }
174
175    static int kthread(void *_create)
176    {
177        /* Copy data: it's on kthread's stack */
178        struct kthread_create_info *create = _create;
179        int (*threadfn)(void *data) = create->threadfn;
180        void *data = create->data;

And earlier:
(gdb) list *ret_from_kernel_thread+0x21
0xc13bb181 is at 
/var/testpoint/LEAF/source/i486-unknown-linux-uclibc/linux/linux-4.1/arch/x86/kernel/entry_32.S:312.
307        popl_cfi %eax
308        pushl_cfi $0x0202        # Reset kernel eflags
309        popfl_cfi
310        movl PT_EBP(%esp),%eax
311        call *PT_EBX(%esp)
312        movl $0,PT_EAX(%esp)
313        jmp syscall_exit
314        CFI_ENDPROC
315    ENDPROC(ret_from_kernel_thread)
316

Stack corruption?..

I'll try to make test environment on real hardware. And I'll try to test 
with older kernels.

22.11.2015 07:17, Alexander Duyck пишет:
> On 11/21/2015 12:16 AM, Andrew wrote:
>> Memory corruption, if happens, IMHO shouldn't be a hardware-related - 
>> almost all of these boxes, except H61M-based box from 1st log, works 
>> for a long time with uptime more than year; and only software was 
>> changed on it; H61M-based box runs memtest86 for a tens of hours w/o 
>> any error. If it was caused by hardware - they should crash even 
>> earlier.
>
> I wasn't saying it was hardware related.  My thought is that it could 
> be some sort of use after free or double free type issue. Basically 
> what you end up with is the memory getting corrupted by software that 
> is accessing regions it shouldn't be.
>
>> Rarely on different servers I saw 'zram decompression error' messages 
>> (in this case I've got such message on H61M-based box).
>>
>> Also, other people that uses accel-ppp as BRAS software, have 
>> different kernel panics/bugs/oopses on fresh kernels.
>>
>> I'll try to apply these patches, and I'll try to switch back to 
>> kernels that were stable on some boxes.
>
> If you could bisect this it would be useful.  Basically we just need 
> to determine where in the git history these issues started popping up 
> so that we can then narrow down on the root cause.
>
> - Alex

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