[PATCH 5.4 375/389] RISC-V: Add fast call path of crash_kexec()

Greg Kroah-Hartman
2022-08-23T12:06:49Z

From: Xianting Tian <xianting.tian@linux.alibaba.com>

[ Upstream commit 3f1901110a89b0e2e13adb2ac8d1a7102879ea98 ]

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@kernel.org>
Tested-by: Xianting Tian <xianting.tian@linux.alibaba.com>
Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220606082308.2883458-1-xianting.tian@linux.alibaba.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 473de3ae8bb7..ae462037910b 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -15,6 +15,7 @@
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/irq.h>
+#include <linux/kexec.h>

#include <asm/processor.h>
#include <asm/ptrace.h>
@@ -43,6 +44,9 @@ void die(struct pt_regs *regs, const char *str)

ret = notify_die(DIE_OOPS, str, regs, 0, regs->scause, 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);
--
2.35.1