linux-kernel - Re: [PATCH v3] RISC-V: Add fixup to support fast call of crash

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Message-ID: <b2a45f97-0f97-6621-bb7e-11f51282c468@huawei.com>
Date:   Tue, 7 Jun 2022 09:21:44 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Xianting Tian <xianting.tian@...ux.alibaba.com>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <philipp.tomsich@...ll.eu>,
        <ebiederm@...ssion.com>, <heiko@...ech.de>,
        <vitaly.wool@...sulko.com>, <tongtiangen@...wei.com>,
        <guoren@...nel.org>
CC:     <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] RISC-V: Add fixup to support fast call of
 crash_kexec()


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@...nel.org>
> Signed-off-by: Xianting Tian <xianting.tian@...ux.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,

Reviewed-by: Kefeng Wang <wangkefeng.wang@...wei.com>

>   	bust_spinlocks(0);
>   	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
>   	spin_unlock_irq(&die_lock);