linux-kernel - Re: [PATCH] riscv: stacktrace: Fix missing the first frame

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Date:   Tue, 6 Dec 2022 16:15:56 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Liu Shixin <liushixin2@...wei.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Changbin Du <changbin.du@...el.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: stacktrace: Fix missing the first frame

On Mon, Dec 05, 2022 at 09:29:36PM +0800, Liu Shixin wrote:
> When running kfence_test, I found some testcases failed like this:
> 
>  # test_out_of_bounds_read: EXPECTATION FAILED at mm/kfence/kfence_test.c:346
>  Expected report_matches(&expect) to be true, but is false
>  not ok 1 - test_out_of_bounds_read
> 
> The corresponding call-trace is:
> 
>  BUG: KFENCE: out-of-bounds read in kunit_try_run_case+0x38/0x84
> 
>  Out-of-bounds read at 0x(____ptrval____) (32B right of kfence-#10):
>   kunit_try_run_case+0x38/0x84
>   kunit_generic_run_threadfn_adapter+0x12/0x1e
>   kthread+0xc8/0xde
>   ret_from_exception+0x0/0xc
> 
> The kfence_test using the first frame of call trace to check whether the
> testcase is succeed or not. Patch a7c5c7e8ff78 skip first frame for all
> case, which results the kfence_test failed. Indeed, we only need to skip
> the first frame for case (task==NULL || task==current).
> 
> With this patch, the call-trace will be:
> 
>  BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0x88/0x19e
> 
>  Out-of-bounds read at 0x(____ptrval____) (1B left of kfence-#7):
>   test_out_of_bounds_read+0x88/0x19e
>   kunit_try_run_case+0x38/0x84
>   kunit_generic_run_threadfn_adapter+0x12/0x1e
>   kthread+0xc8/0xde
>   ret_from_exception+0x0/0xc
> 
> Fixes: a7c5c7e8ff78 ("riscv: eliminate unreliable __builtin_frame_address(1)")

This fixes tag is not right, did checkpatch not warn about it?

The correct fixes tag would be:
Fixes: 6a00ef449370 ("riscv: eliminate unreliable __builtin_frame_address(1)")

Maybe consider automating the creation of fixes tags, like so:
git log -1 --format='Fixes: %h (\"%s\")'

Thanks,
Conor.

> Signed-off-by: Liu Shixin <liushixin2@...wei.com>
> ---
>  arch/riscv/kernel/stacktrace.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
> index 08d11a53f39e..5fe2ae4cf135 100644
> --- a/arch/riscv/kernel/stacktrace.c
> +++ b/arch/riscv/kernel/stacktrace.c
> @@ -30,6 +30,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
>  		fp = (unsigned long)__builtin_frame_address(0);
>  		sp = current_stack_pointer;
>  		pc = (unsigned long)walk_stackframe;
> +		level = -1;
>  	} else {
>  		/* task blocked in __switch_to */
>  		fp = task->thread.s[0];
> @@ -41,7 +42,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
>  		unsigned long low, high;
>  		struct stackframe *frame;
>  
> -		if (unlikely(!__kernel_text_address(pc) || (level++ >= 1 && !fn(arg, pc))))
> +		if (unlikely(!__kernel_text_address(pc) || (level++ >= 0 && !fn(arg, pc))))
>  			break;
>  
>  		/* Validate frame pointer */
> -- 
> 2.25.1
> 

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