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Subject: Re: [PATCH] RISC-V: Add fast call path of crash_kexec()
To:     paul.walmsley@sifive.com, aou@eecs.berkeley.edu,
        palmer@dabbelt.com, wangkefeng.wang@huawei.com,
        vitaly.wool@konsulko.com, rmk+kernel@armlinux.org.uk,
        ebiederm@xmission.com, tongtiangen@huawei.co
Cc:     linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        guoren@kernel.org, mick@ics.forth.gr
References: <20220515131407.946832-1-xianting.tian@linux.alibaba.com>
From:   Xianting Tian <xianting.tian@linux.alibaba.com>
Message-ID: <788c0f2a-1562-b4ca-a1ca-0289032b1f8a@linux.alibaba.com>
Date:   Tue, 24 May 2022 09:50:42 +0800
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just a friendly ping

?? 2022/5/15 ????9:14, Xianting Tian д??:
> 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/virtio/virtio_mmio.c:806
> 	806             *(int *)p = 0xdead;
> 	(gdb)
> 	(gdb) bt
> 	#0  0xffffffe00063a4e0 in test_thread (data=<optimized out>) at drivers/virtio/virtio_mmio.c:806
> 	#1  0x0000000000000000 in ?? ()
>
> Test code to produce NULL address dereference,
> 	+extern int panic_on_oops;
> 	+static struct task_struct *k;
> 	+static int test_thread(void *data) {
> 	+
> 	+       void *p = NULL;
> 	+
> 	+       while (!panic_on_oops)
> 	+               msleep(2000);
> 	+
> 	+       *(int *)p = 0xdead;
> 	+
> 	+       return 0;
> 	+}
> 	+
> 	 static int __init virtio_mmio_init(void)
> 	 {
> 	+       k = kthread_run(test_thread, NULL, "test_thread");
> 	+       if (IS_ERR(k))
> 	+               pr_err("Couldn't create test kthread\n");
> 	+
> 	        return platform_driver_register(&virtio_mmio_driver);
> 	 }
>
> Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
> ---
>   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);