[RFC PATCH] riscv: stacktrace: fix the riscv stacktrace when CONFIG_FRAME_POINTER enabled

[Palmer Dabbelt]

On Thu, 29 Apr 2021 00:03:48 PDT (-0700), chenhuang5 at huawei.com wrote:
> As [1] and [2] said, the arch_stack_walk should not to trace itself, or it will
> leave the trace unexpectedly when called. The example is when we do "cat
> /sys/kernel/debug/page_owner", all pages' stack is the same.
>
> arch_stack_walk+0x18/0x20
> stack_trace_save+0x40/0x60
> register_dummy_stack+0x24/0x5e
> init_page_owner+0x2e
>
> So we use __builtin_frame_address(1) as the first frame to be walked. And mark
> the arch_stack_walk() noinline.
>
> We found that pr_cont will affact pages' stack whose task state is RUNNING when
> testing "echo t > /proc/sysrq-trigger". So move the place of pr_cont and mark
> the function dump_backtrace() noinline.
>
> Also we move the case when task == NULL into else branch, and test for it in
> "echo c > /proc/sysrq-trigger".
>
> [1] https://lore.kernel.org/lkml/20210319184106.5688-1-mark.rutland@arm.com/
> [2] https://lore.kernel.org/lkml/20210317142050.57712-1-chenjun102@huawei.com/
>
> Signed-off-by: Chen Huang <chenhuang5 at huawei.com>
> ---
> In this way, some crash will loss the print info "Call trace:", likes that:
> # echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
> [   61.774690] lkdtm: Performing direct entry BUG
> [   61.775350] ------------[ cut here ]------------
> [   61.775611] kernel BUG at drivers/misc/lkdtm/bugs.c:76!
> [   61.776073] Kernel BUG [#1]
> [   61.776319] Modules linked in:
> [   61.776696] CPU: 3 PID: 1 Comm: sh Not tainted 5.11.0-rc6-next-20210208-00013-gb16da2c3b9aa #132
> [   61.777185] Hardware name: riscv-virtio,qemu (DT)
> [   61.777594] epc : lkdtm_BUG+0x6/0x8
> [   61.777916]  ra : lkdtm_do_action+0x14/0x1c
> [   61.778212] epc : ffffffe00048a7e8 ra : ffffffe0006d71a8 sp : ffffffe07fedbd90
> [   61.778646]  gp : ffffffe0012e4208 tp : ffffffe07fed0000 t0 : ffffffe0012f2097
> [   61.779115]  t1 : ffffffe0012f2088 t2 : 0000000000000000 s0 : ffffffe07fedbda0
> [   61.779588]  s1 : 0000000000000010 a0 : ffffffe000c7fbb8 a1 : ffffffe001284d28
> [   61.780017]  a2 : 0000000000000010 a3 : 0000000000000000 a4 : c10724222fbe9200
> [   61.780473]  a5 : ffffffe00048a7e2 a6 : c0000000ffffefff a7 : 0000000000000064
> [   61.780932]  s2 : ffffffe000c7fbc8 s3 : ffffffe000d9e3f8 s4 : ffffffe081969000
> [   61.781405]  s5 : 000000000000004b s6 : 0000000000000004 s7 : ffffffe07fedbe80
> [   61.781872]  s8 : 0000003ffff987e4 s9 : 0000002ab0b7ac50 s10: 0000002ab0bacb90
> [   61.782336]  s11: 0000000000000000 t3 : 000000000000006c t4 : ffffffffffffffff
> [   61.782794]  t5 : 0000000000000037 t6 : ffffffe07fedbae8
> [   61.783158] status: 0000000000000120 badaddr: 0000000000000000 cause: 0000000000000003
> [   61.783680] [<ffffffe00048a7e8>] lkdtm_BUG+0x6/0x8
> [   61.784149] [<ffffffe0006d71a8>] lkdtm_do_action+0x14/0x1c
> [   61.784516] [<ffffffe00048a5ee>] direct_entry+0xc0/0x10a
> [   61.784849] [<ffffffe0002498ce>] full_proxy_write+0x42/0x6a
> [   61.785209] [<ffffffe000114b7c>] vfs_write+0x7e/0x218
> [   61.785562] [<ffffffe000114e84>] ksys_write+0x98/0xc0
> [   61.785904] [<ffffffe000114eba>] sys_write+0xe/0x16
> [   61.786275] [<ffffffe000003466>] ret_from_syscall+0x0/0x2
> [   61.787175] ---[ end trace 6919e7283b64f492 ]---
> [   61.787707] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
> [   61.788270] SMP: stopping secondary CPUs
> [   61.788934] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---
>
>  arch/riscv/kernel/stacktrace.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
> index 2b3e0cb90d78..bde85fc53357 100644
> --- a/arch/riscv/kernel/stacktrace.c
> +++ b/arch/riscv/kernel/stacktrace.c
> @@ -27,10 +27,10 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
>  		fp = frame_pointer(regs);
>  		sp = user_stack_pointer(regs);
>  		pc = instruction_pointer(regs);
> -	} else if (task == NULL || task == current) {
> -		fp = (unsigned long)__builtin_frame_address(0);
> -		sp = sp_in_global;
> -		pc = (unsigned long)walk_stackframe;
> +	} else if (task == current) {
> +		fp = (unsigned long)__builtin_frame_address(1);
> +		sp = (unsigned long)__builtin_frame_address(0);
> +		pc = (unsigned long)__builtin_return_address(0);
>  	} else {
>  		/* task blocked in __switch_to */
>  		fp = task->thread.s[0];
> @@ -106,15 +106,15 @@ static bool print_trace_address(void *arg, unsigned long pc)
>  	return true;
>  }
>
> -void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
> +noinline void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
>  		    const char *loglvl)
>  {
> -	pr_cont("%sCall Trace:\n", loglvl);
>  	walk_stackframe(task, regs, print_trace_address, (void *)loglvl);
>  }
>
>  void show_stack(struct task_struct *task, unsigned long *sp, const char *loglvl)
>  {
> +	pr_cont("%sCall Trace:\n", loglvl);
>  	dump_backtrace(NULL, task, loglvl);
>  }
>
> @@ -139,7 +139,7 @@ unsigned long get_wchan(struct task_struct *task)
>
>  #ifdef CONFIG_STACKTRACE
>
> -void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
> +noinline void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
>  		     struct task_struct *task, struct pt_regs *regs)
>  {
>  	walk_stackframe(task, regs, consume_entry, cookie);

Thanks, this is on fixes.