On 12/09/16 at 03:16pm, Xunlei Pang wrote:
> 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?
It's very interesting. I got the different result by mental arithmatic.
Assume nr_segments is 16, and they are placed in continuous physical
memory, then in the first while loop, it will failed in image->segment[0]
and adjust hole_start and hole_end. Then it failed in 2nd while loop
after comparing with image->segment[0] and image->segment[1]. Finally it
will get a new position after image->segment[15] after 16 comparision in
the 16th while loop. So the amount should be (1+2+3+3+16) which is
(1+16)*8, 136 times.
Not sure if the counting is right, I am wondering how it will loop
millions of times even though crashk_res.end will exceed to 4G. The
times should not be related to how much memory resreved, only the
nr_segments, maybe I am wrong.
Thanks
Baoquan
