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Subject: Re: [PATCH] powerpc/kdump: fix kdump kernel hangup issue with hot add
 CPUs
To:     Sourabh Jain <sourabhjain@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>
From:   Hari Bathini <hbathini@linux.ibm.com>
Message-ID: <b8f5fad8-3ea8-cb8d-84d2-8769ed41cc38@linux.ibm.com>
Date:   Fri, 16 Apr 2021 15:03:38 +0530
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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>

>   /**
>    * 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?


Thanks
Hari