linux-kernel - Re: [RESEND PATCH v2] RISC-V: Add fast call path of crash

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Date:   Thu, 21 Jul 2022 17:11:06 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     xianting.tian@...ux.alibaba.com
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        wangkefeng.wang@...wei.com, philipp.tomsich@...ll.eu,
        ebiederm@...ssion.com, heiko@...ech.de, vitaly.wool@...sulko.com,
        tongtiangen@...wei.com, guoren@...nel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        xianting.tian@...ux.alibaba.com
Subject:     Re: [RESEND PATCH v2] RISC-V: Add fast call path of crash_kexec()

On Mon, 06 Jun 2022 01:23:08 PDT (-0700), xianting.tian@...ux.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@...nel.org>
> Tested-by: Xianting Tian <xianting.tian@...ux.alibaba.com>
> Signed-off-by: Xianting Tian <xianting.tian@...ux.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.