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

[Xianting Tian]

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@xxxxxxxxxx>
> > Signed-off-by: Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx>
> > ---
> > 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@xxxxxxxxxx>
>
> >       bust_spinlocks(0);
> >       add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
> >       spin_unlock_irq(&die_lock);