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

From: Xianting Tian
Date: Fri Jun 17 2022 - 02:40:52 EST


Hi Palmer

Will you apply this patch for 5.19?

thanks

在 2022/6/7 上午9:46, Xianting Tian 写道:

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);