On 12/09/2016 at 01:13 PM, zhong jiang wrote:
> On 2016/12/8 17:41, Xunlei Pang wrote:
>> On 12/08/2016 at 10:37 AM, zhongjiang wrote:
>>> From: zhong jiang <zhongjiang at huawei.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 at huawei.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....
How does "loop million times" happen? See my inlined comments prefixed with "pxl".
kimage_alloc_crash_control_pages():
while (hole_end <= crashk_res.end) {
unsigned long i;
if (hole_end > KEXEC_CRASH_CONTROL_MEMORY_LIMIT)
break;
/* See if I overlap any of the segments */
for (i = 0; i < image->nr_segments; i++) { // pxl: max 16 loops, all existent segments are not overlapped, though may not sorted.
unsigned long mstart, mend;
mstart = image->segment[i].mem;
mend = mstart + image->segment[i].memsz - 1;
if ((hole_end >= mstart) && (hole_start <= mend)) {
/* Advance the hole to the end of the segment */
hole_start = (mend + (size - 1)) & ~(size - 1);
hole_end = hole_start + size - 1;
break; // pxl: If overlap was found, break for loop, @hole_end starts after the overlapped segment area, and will while loop again
}
}
/* If I don't overlap any segments I have found my hole! */
if (i == image->nr_segments) {
pages = pfn_to_page(hole_start >> PAGE_SHIFT);
image->control_page = hole_end;
break; // pxl: no overlap with all the segments, get the result and break the while loop. END.
}
}
So, the worst "while" loops in theory would be (image->nr_segments + 1), no?
Regards,
Xunlei
