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Date:   Tue, 6 Dec 2022 16:15:56 +0000
From:   Conor Dooley <conor@kernel.org>
To:     Liu Shixin <liushixin2@huawei.com>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Changbin Du <changbin.du@intel.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: stacktrace: Fix missing the first frame
Message-ID: <Y49qvHb3LVas1cvO@spud>
References: <20221205132936.493245-1-liushixin2@huawei.com>
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On Mon, Dec 05, 2022 at 09:29:36PM +0800, Liu Shixin wrote:
> When running kfence_test, I found some testcases failed like this:
>=20
>  # 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
>=20
> The corresponding call-trace is:
>=20
>  BUG: KFENCE: out-of-bounds read in kunit_try_run_case+0x38/0x84
>=20
>  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
>=20
> 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=3D=3DNULL || task=3D=3Dcurrent).
>=20
> With this patch, the call-trace will be:
>=20
>  BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0x88/0x19e
>=20
>  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
>=20
> 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=3D'Fixes: %h (\"%s\")'

Thanks,
Conor.

> Signed-off-by: Liu Shixin <liushixin2@huawei.com>
> ---
>  arch/riscv/kernel/stacktrace.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>=20
> diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrac=
e.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 =3D (unsigned long)__builtin_frame_address(0);
>  		sp =3D current_stack_pointer;
>  		pc =3D (unsigned long)walk_stackframe;
> +		level =3D -1;
>  	} else {
>  		/* task blocked in __switch_to */
>  		fp =3D 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;
> =20
> -		if (unlikely(!__kernel_text_address(pc) || (level++ >=3D 1 && !fn(arg,=
 pc))))
> +		if (unlikely(!__kernel_text_address(pc) || (level++ >=3D 0 && !fn(arg,=
 pc))))
>  			break;
> =20
>  		/* Validate frame pointer */
> --=20
> 2.25.1
>=20

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