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Subject: Re: [PATCH] powerpc/kdump: fix kdump kernel hangup issue with hot add
 CPUs
To:     Hari Bathini <hbathini@linux.ibm.com>, mpe@ellerman.id.au
Cc:     mahesh@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
        linuxppc-dev@ozlabs.org
References: <20210416064749.657585-1-sourabhjain@linux.ibm.com>
 <b8f5fad8-3ea8-cb8d-84d2-8769ed41cc38@linux.ibm.com>
From:   Sourabh Jain <sourabhjain@linux.ibm.com>
Message-ID: <e478b65c-d41d-48e7-2d11-7cef8bb6f274@linux.ibm.com>
Date:   Fri, 16 Apr 2021 16:57:55 +0530
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On 16/04/21 3:03 pm, Hari Bathini wrote:
>
>
> On 16/04/21 12:17 pm, Sourabh Jain wrote:
>> With the kexec_file_load system call when system crashes on the hot add
>> CPU the capture kernel hangs and failed to collect the vmcore.
>>
>>   Kernel panic - not syncing: sysrq triggered crash
>>   CPU: 24 PID: 6065 Comm: echo Kdump: loaded Not tainted 
>> 5.12.0-rc5upstream #54
>>   Call Trace:
>>   [c0000000e590fac0] [c0000000007b2400] dump_stack+0xc4/0x114 
>> (unreliable)
>>   [c0000000e590fb00] [c000000000145290] panic+0x16c/0x41c
>>   [c0000000e590fba0] [c0000000008892e0] sysrq_handle_crash+0x30/0x40
>>   [c0000000e590fc00] [c000000000889cdc] __handle_sysrq+0xcc/0x1f0
>>   [c0000000e590fca0] [c00000000088a538] write_sysrq_trigger+0xd8/0x178
>>   [c0000000e590fce0] [c0000000005e9b7c] proc_reg_write+0x10c/0x1b0
>>   [c0000000e590fd10] [c0000000004f26d0] vfs_write+0xf0/0x330
>>   [c0000000e590fd60] [c0000000004f2aec] ksys_write+0x7c/0x140
>>   [c0000000e590fdb0] [c000000000031ee0] 
>> system_call_exception+0x150/0x290
>>   [c0000000e590fe10] [c00000000000ca5c] system_call_common+0xec/0x278
>>   --- interrupt: c00 at 0x7fff905b9664
>>   NIP:  00007fff905b9664 LR: 00007fff905320c4 CTR: 0000000000000000
>>   REGS: c0000000e590fe80 TRAP: 0c00   Not tainted (5.12.0-rc5upstream)
>>   MSR:  800000000280f033 <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE>  CR: 
>> 28000242
>>         XER: 00000000
>>   IRQMASK: 0
>>   GPR00: 0000000000000004 00007ffff5fedf30 00007fff906a7300 
>> 0000000000000001
>>   GPR04: 000001002a7355b0 0000000000000002 0000000000000001 
>> 00007ffff5fef616
>>   GPR08: 0000000000000001 0000000000000000 0000000000000000 
>> 0000000000000000
>>   GPR12: 0000000000000000 00007fff9073a160 0000000000000000 
>> 0000000000000000
>>   GPR16: 0000000000000000 0000000000000000 0000000000000000 
>> 0000000000000000
>>   GPR20: 0000000000000000 00007fff906a4ee0 0000000000000002 
>> 0000000000000001
>>   GPR24: 00007fff906a0898 0000000000000000 0000000000000002 
>> 000001002a7355b0
>>   GPR28: 0000000000000002 00007fff906a1790 000001002a7355b0 
>> 0000000000000002
>>   NIP [00007fff905b9664] 0x7fff905b9664
>>   LR [00007fff905320c4] 0x7fff905320c4
>>   --- interrupt: c00
>
> <SNIP>
>
> I will update the commit message.
>
>>   /**
>>    * setup_new_fdt_ppc64 - Update the flattend device-tree of the kernel
>>    *                       being loaded.
>> @@ -1020,6 +1113,13 @@ int setup_new_fdt_ppc64(const struct kimage 
>> *image, void *fdt,
>>           }
>>       }
>>   +    /* Update cpus nodes information to account hotplug CPUs. */
>> +    if (image->type == KEXEC_TYPE_CRASH) {
>
> Shouldn't this apply to regular kexec_file_load case as well? Yeah, 
> there won't be a hang in regular kexec_file_load case but for 
> correctness, that kernel should also not see stale CPU info in FDT?
>
> Yes better to update the fdt for both kexec and kdump.
>
> Thanks for the review Hari.
>
> - Sourabh Jain