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Subject: Re: [RESEND PATCH v2] RISC-V: Add fast call path of crash_kexec()
To:     Palmer Dabbelt <palmer@dabbelt.com>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>, aou@eecs.berkeley.edu,
        wangkefeng.wang@huawei.com, philipp.tomsich@vrull.eu,
        ebiederm@xmission.com, heiko@sntech.de, vitaly.wool@konsulko.com,
        tongtiangen@huawei.com, guoren@kernel.org,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
References: <mhng-c42cbd7f-4935-4d16-9150-5504fd06aedd@palmer-mbp2014>
From:   tianxianting <xianting.tian@linux.alibaba.com>
Message-ID: <6412d106-24c0-a2ad-79b9-de6664c8723d@linux.alibaba.com>
Date:   Fri, 22 Jul 2022 11:41:07 +0800
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在 2022/7/22 上午8:11, Palmer Dabbelt 写道:
> On Mon, 06 Jun 2022 01:23:08 PDT (-0700), 
> xianting.tian@linux.alibaba.com wrote:
>> Currently, almost all archs (x86, arm64, mips...) support fast call
>> of crash_kexec() when "regs && kexec_should_crash()" is true. But
>> RISC-V not, it can only enter crash system via panic(). However panic()
>> doesn't pass the regs of the real accident scene to crash_kexec(),
>> it caused we can't get accurate backtrace via gdb,
>>     $ riscv64-linux-gnu-gdb vmlinux vmcore
>>     Reading symbols from vmlinux...
>>     [New LWP 95]
>>     #0  console_unlock () at kernel/printk/printk.c:2557
>>     2557                    if (do_cond_resched)
>>     (gdb) bt
>>     #0  console_unlock () at kernel/printk/printk.c:2557
>>     #1  0x0000000000000000 in ?? ()
>>
>> With the patch we can get the accurate backtrace,
>>     $ riscv64-linux-gnu-gdb vmlinux vmcore
>>     Reading symbols from vmlinux...
>>     [New LWP 95]
>>     #0  0xffffffe00063a4e0 in test_thread (data=<optimized out>) at 
>> drivers/test_crash.c:81
>>     81             *(int *)p = 0xdead;
>>     (gdb)
>>     (gdb) bt
>>     #0  0xffffffe00064d5c0 in test_thread (data=<optimized out>) at 
>> drivers/test_crash.c:81
>>     #1  0x0000000000000000 in ?? ()
>>
>> Test code to produce NULL address dereference in test_crash.c,
>>     void *p = NULL;
>>     *(int *)p = 0xdead;
>>
>> Reviewed-by: Guo Ren <guoren@kernel.org>
>> Tested-by: Xianting Tian <xianting.tian@linux.alibaba.com>
>> Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
>> ---
>> Changes from v1:
>> - simplify the commit message
>> ---
>>  arch/riscv/kernel/traps.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
>> index fe92e119e6a3..e666ebfa2a64 100644
>> --- a/arch/riscv/kernel/traps.c
>> +++ b/arch/riscv/kernel/traps.c
>> @@ -16,6 +16,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/module.h>
>>  #include <linux/irq.h>
>> +#include <linux/kexec.h>
>>
>>  #include <asm/asm-prototypes.h>
>>  #include <asm/bug.h>
>> @@ -44,6 +45,9 @@ void die(struct pt_regs *regs, const char *str)
>>
>>      ret = notify_die(DIE_OOPS, str, regs, 0, regs->cause, SIGSEGV);
>>
>> +    if (regs && kexec_should_crash(current))
>> +        crash_kexec(regs);
>> +
>>      bust_spinlocks(0);
>>      add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
>>      spin_unlock_irq(&die_lock);
>
> Thanks, this is on for-next.

Palmer, thanks for the reply,

Last week, I commit a series of 
patches(https://lkml.org/lkml/2022/7/17/64 
<https://lkml.org/lkml/2022/7/17/64>), which contains this one.

This series of patches worked with crash-utility for RISCV64, Could you 
please review it?

We expect 5.19 could support crash-utility, it is a good functionality.

crash-utility patches for RISCV64:

https://lore.kernel.org/all/20220718025346.411758-1-xianting.tian@linux.alibaba.com/ 
<https://lore.kernel.org/all/20220718025346.411758-1-xianting.tian@linux.alibaba.com/>