From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753708AbcLIHPD (ORCPT ); Fri, 9 Dec 2016 02:15:03 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33264 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751302AbcLIHPC (ORCPT ); Fri, 9 Dec 2016 02:15:02 -0500 Reply-To: xlpang@redhat.com Subject: Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages References: <1481164674-42775-1-git-send-email-zhongjiang@huawei.com> <58492ADC.4070305@redhat.com> <584A3D84.6040004@huawei.com> To: zhong jiang , xlpang@redhat.com Cc: akpm@linux-foundation.org, kexec@lists.infradead.org, ebiederm@xmission.com, linux-kernel@vger.kernel.org From: Xunlei Pang Message-ID: <584A5A47.6040602@redhat.com> Date: Fri, 9 Dec 2016 15:16:23 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <584A3D84.6040004@huawei.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 09 Dec 2016 07:15:02 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >>> >>> 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] [] dump_stack+0x19/0x1b >>> [ 237.301352] [] panic+0xd8/0x214 >>> [ 237.306196] [] watchdog_timer_fn+0x1cc/0x1e0 >>> [ 237.312157] [] ? watchdog_enable+0xc0/0xc0 >>> [ 237.317955] [] __hrtimer_run_queues+0xd2/0x260 >>> [ 237.324087] [] hrtimer_interrupt+0xb0/0x1e0 >>> [ 237.329963] [] ? call_softirq+0x1c/0x30 >>> [ 237.335500] [] local_apic_timer_interrupt+0x37/0x60 >>> [ 237.342228] [] smp_apic_timer_interrupt+0x3f/0x60 >>> [ 237.348771] [] apic_timer_interrupt+0x6d/0x80 >>> [ 237.354967] [] ? kimage_alloc_control_pages+0x80/0x270 >>> [ 237.362875] [] ? kmem_cache_alloc_trace+0x1ce/0x1f0 >>> [ 237.369592] [] ? do_kimage_alloc_init+0x1f/0x90 >>> [ 237.375992] [] kimage_alloc_init+0x12a/0x180 >>> [ 237.382103] [] SyS_kexec_load+0x20a/0x260 >>> [ 237.387957] [] 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 >>> --- >>> 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