[PATCH] RISC-V: Add fast call path of crash_kexec()

[Guo Ren]

Great Job, I think it's a fixup, we should add Fix: and Cc: stable at kernel.org

Reviewed-by: Guo Ren <guoren at kernel.org>

On Sun, May 15, 2022 at 9:14 PM Xianting Tian
<xianting.tian at 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/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 at 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);
> --
> 2.17.1
>


-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/