Re: [PATCH v3] RISC-V: Add fixup to support fast call of crash_kexec()

[Xianting Tian <xianting.tian@linux.alibaba.com>]

Hi Palmer

Will you apply this patch for 5.19?

thanks

在 2022/6/7 上午9:46, Xianting Tian 写道:
>
> 在 2022/6/7 上午9:21, Kefeng Wang 写道:
>>
>> On 2022/6/6 20:37, Xianting Tian 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;
>>>
>>> Fixes: 76d2a0493a17 ("RISC-V: Init and Halt Code")
>>> Reviewed-by: Guo Ren <guoren@kernel.org>
>>> Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
>>> ---
>>> Changes from v1:
>>> - simplify the commit message
>>> Changes from v2:
>>> - add fixup in title
>>> ---
>>>   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 b40426509244..39d0f8bba4b4 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);
>>> +
>>
>> It seems that the regs won't be null, right? except that,
>
> Autually both regs won't be null, But if it is triggered by panic() , 
> the regs are got via riscv_crash_save_regs(), which are the regs of 
> that moment, but not the real accident scene.
>
>>
>> Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>>
>>>       bust_spinlocks(0);
>>>       add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
>>>       spin_unlock_irq(&die_lock);

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