linux-kernel - Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control

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Date:   Fri, 9 Dec 2016 13:13:40 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     <xlpang@...hat.com>
CC:     Xunlei Pang <xpang@...hat.com>, <ebiederm@...ssion.com>,
        <akpm@...ux-foundation.org>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages

On 2016/12/8 17:41, Xunlei Pang wrote:
> On 12/08/2016 at 10:37 AM, zhongjiang wrote:
>> From: zhong jiang <zhongjiang@...wei.com>
>>
>> A soft lookup will occur when I run trinity in syscall kexec_load.
>> the corresponding stack information is as follows.
>>
>> [  237.235937] BUG: soft lockup - CPU#6 stuck for 22s! [trinity-c6:13859]
>> [  237.242699] Kernel panic - not syncing: softlockup: hung tasks
>> [  237.248573] CPU: 6 PID: 13859 Comm: trinity-c6 Tainted: G           O L ----V-------   3.10.0-327.28.3.35.zhongjiang.x86_64 #1
>> [  237.259984] Hardware name: Huawei Technologies Co., Ltd. Tecal BH622 V2/BC01SRSA0, BIOS RMIBV386 06/30/2014
>> [  237.269752]  ffffffff8187626b 0000000018cfde31 ffff88184c803e18 ffffffff81638f16
>> [  237.277471]  ffff88184c803e98 ffffffff8163278f 0000000000000008 ffff88184c803ea8
>> [  237.285190]  ffff88184c803e48 0000000018cfde31 ffff88184c803e67 0000000000000000
>> [  237.292909] Call Trace:
>> [  237.295404]  <IRQ>  [<ffffffff81638f16>] dump_stack+0x19/0x1b
>> [  237.301352]  [<ffffffff8163278f>] panic+0xd8/0x214
>> [  237.306196]  [<ffffffff8111d6fc>] watchdog_timer_fn+0x1cc/0x1e0
>> [  237.312157]  [<ffffffff8111d530>] ? watchdog_enable+0xc0/0xc0
>> [  237.317955]  [<ffffffff810aa182>] __hrtimer_run_queues+0xd2/0x260
>> [  237.324087]  [<ffffffff810aa720>] hrtimer_interrupt+0xb0/0x1e0
>> [  237.329963]  [<ffffffff8164ae5c>] ? call_softirq+0x1c/0x30
>> [  237.335500]  [<ffffffff81049a77>] local_apic_timer_interrupt+0x37/0x60
>> [  237.342228]  [<ffffffff8164bacf>] smp_apic_timer_interrupt+0x3f/0x60
>> [  237.348771]  [<ffffffff8164a11d>] apic_timer_interrupt+0x6d/0x80
>> [  237.354967]  <EOI>  [<ffffffff810f3a00>] ? kimage_alloc_control_pages+0x80/0x270
>> [  237.362875]  [<ffffffff811c3ebe>] ? kmem_cache_alloc_trace+0x1ce/0x1f0
>> [  237.369592]  [<ffffffff810f362f>] ? do_kimage_alloc_init+0x1f/0x90
>> [  237.375992]  [<ffffffff810f3d1a>] kimage_alloc_init+0x12a/0x180
>> [  237.382103]  [<ffffffff810f3f9a>] SyS_kexec_load+0x20a/0x260
>> [  237.387957]  [<ffffffff816494c9>] system_call_fastpath+0x16/0x1b
>>
>> the first time allocate control pages may take too much time because
>> crash_res.end can be set to a higher value. we need to add cond_resched
>> to avoid the issue.
>>
>> The patch have been tested and above issue is not appear.
>>
>> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
>> ---
>>  kernel/kexec_core.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>> index 5616755..bfc9621 100644
>> --- a/kernel/kexec_core.c
>> +++ b/kernel/kexec_core.c
>> @@ -441,6 +441,8 @@ static struct page *kimage_alloc_crash_control_pages(struct kimage *image,
>>  	while (hole_end <= crashk_res.end) {
>>  		unsigned long i;
>>  
>> +		cond_resched();
>> +
> I can't see why it would take a long time to loop inside, the job it does is simply to find a control area
> not overlapped with image->segment[], you can see the loop "for (i = 0; i < image->nr_segments; i++)",
> @hole_end will be advanced to the end of its next nearby segment once overlap was detected each loop,
> also there are limited (<=16) segments, so it won't take long to locate the right area.
>
> Am I missing something?
>
> Regards,
> Xunlei
  if the crashkernel = auto is set in cmdline.  it represent crashk_res.end will exceed to 4G, the first allocate control pages will
  loop  million times. if we set crashk_res.end to the higher value manually,  you can image....

  Thanks
  zhongjiang
>>  		if (hole_end > KEXEC_CRASH_CONTROL_MEMORY_LIMIT)
>>  			break;
>>  		/* See if I overlap any of the segments */
>
> .
>