[PATCH kernel] powerpc/debug: Add missing warn flag to WARN_ON's non-builtin path

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[PATCH kernel] powerpc/debug: Add missing warn flag to WARN_ON's non-builtin path

Alexey Kardashevskiy
When trapped on WARN_ON(), report_bug() is expected to return
BUG_TRAP_TYPE_WARN so the caller could increment NIP by 4 and continue.
The __builtin_constant_p() path of the PPC's WARN_ON() calls (indirectly)
__WARN_FLAGS() which has BUGFLAG_WARNING set, however the other branch
does not which makes report_bug() report a bug rather than a warning.

Fixes: 19d436268dde95389 ("debug: Add _ONCE() logic to report_bug()")
Signed-off-by: Alexey Kardashevskiy <[hidden email]>
---

Actually 19d436268dde95389 replaced __WARN_TAINT() with __WARN_FLAGS()
and lost BUGFLAG_TAINT() and this is not in the commit log so it is
unclear:
1) why
2) whether this particular patch should be doing
   BUGFLAG_WARNING|BUGFLAG_TAINT(TAINT_WARN)
 or
   BUGFLAG_WARNING|(flags)

Any ideas? Thanks.


---
 arch/powerpc/include/asm/bug.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index f2c562a0a427..0151af6c2a50 100644
--- a/arch/powerpc/include/asm/bug.h
+++ b/arch/powerpc/include/asm/bug.h
@@ -104,7 +104,7 @@
  "1: "PPC_TLNEI" %4,0\n" \
  _EMIT_BUG_ENTRY \
  : : "i" (__FILE__), "i" (__LINE__), \
-  "i" (BUGFLAG_TAINT(TAINT_WARN)), \
+  "i" (BUGFLAG_WARNING|BUGFLAG_TAINT(TAINT_WARN)),\
   "i" (sizeof(struct bug_entry)), \
   "r" (__ret_warn_on)); \
  } \
--
2.11.0

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Re: [PATCH kernel] powerpc/debug: Add missing warn flag to WARN_ON's non-builtin path

Michael Ellerman-2
Alexey Kardashevskiy <[hidden email]> writes:

> When trapped on WARN_ON(), report_bug() is expected to return
> BUG_TRAP_TYPE_WARN so the caller could increment NIP by 4 and continue.
> The __builtin_constant_p() path of the PPC's WARN_ON() calls (indirectly)
> __WARN_FLAGS() which has BUGFLAG_WARNING set, however the other branch
> does not which makes report_bug() report a bug rather than a warning.
>
> Fixes: 19d436268dde95389 ("debug: Add _ONCE() logic to report_bug()")
> Signed-off-by: Alexey Kardashevskiy <[hidden email]>
> ---
>
> Actually 19d436268dde95389 replaced __WARN_TAINT() with __WARN_FLAGS()
> and lost BUGFLAG_TAINT() and this is not in the commit log so it is
> unclear:
> 1) why

I think the rename is because previously the argument was a taint value,
whereas now it is a flags value (which is a superset of taint).

> 2) whether this particular patch should be doing
>    BUGFLAG_WARNING|BUGFLAG_TAINT(TAINT_WARN)
>  or
>    BUGFLAG_WARNING|(flags)

There is no flags here so the latter won't work AFAICS.

> Any ideas? Thanks.

Your patch looks correct to me. I assume it works?


The bug isn't introduced by 19d436268dde ("debug: Add _ONCE() logic to
report_bug()") as far as I can see.

If you check out that revision you see that BUGFLAG_TAINT still contains
BUGFLAG_WARNING:

#define BUGFLAG_TAINT(taint) (BUGFLAG_WARNING | ((taint) << 8))

But that was removed in f26dee15103f ("debug: Avoid setting
BUGFLAG_WARNING twice"). So I think the Fixes: tag should point at that
commit.

cheers

> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index f2c562a0a427..0151af6c2a50 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -104,7 +104,7 @@
>   "1: "PPC_TLNEI" %4,0\n" \
>   _EMIT_BUG_ENTRY \
>   : : "i" (__FILE__), "i" (__LINE__), \
> -  "i" (BUGFLAG_TAINT(TAINT_WARN)), \
> +  "i" (BUGFLAG_WARNING|BUGFLAG_TAINT(TAINT_WARN)),\
>    "i" (sizeof(struct bug_entry)), \
>    "r" (__ret_warn_on)); \
>   } \
> --
> 2.11.0
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Re: [PATCH kernel] powerpc/debug: Add missing warn flag to WARN_ON's non-builtin path

Alexey Kardashevskiy
On 14/06/17 21:04, Michael Ellerman wrote:

> Alexey Kardashevskiy <[hidden email]> writes:
>
>> When trapped on WARN_ON(), report_bug() is expected to return
>> BUG_TRAP_TYPE_WARN so the caller could increment NIP by 4 and continue.
>> The __builtin_constant_p() path of the PPC's WARN_ON() calls (indirectly)
>> __WARN_FLAGS() which has BUGFLAG_WARNING set, however the other branch
>> does not which makes report_bug() report a bug rather than a warning.
>>
>> Fixes: 19d436268dde95389 ("debug: Add _ONCE() logic to report_bug()")
>> Signed-off-by: Alexey Kardashevskiy <[hidden email]>
>> ---
>>
>> Actually 19d436268dde95389 replaced __WARN_TAINT() with __WARN_FLAGS()
>> and lost BUGFLAG_TAINT() and this is not in the commit log so it is
>> unclear:
>> 1) why
>
> I think the rename is because previously the argument was a taint value,
> whereas now it is a flags value (which is a superset of taint).
>
>> 2) whether this particular patch should be doing
>>    BUGFLAG_WARNING|BUGFLAG_TAINT(TAINT_WARN)
>>  or
>>    BUGFLAG_WARNING|(flags)
>
> There is no flags here so the latter won't work AFAICS.
>
>> Any ideas? Thanks.
>
> Your patch looks correct to me. I assume it works?

Yes, it does.

>
>
> The bug isn't introduced by 19d436268dde ("debug: Add _ONCE() logic to
> report_bug()") as far as I can see.
>
> If you check out that revision you see that BUGFLAG_TAINT still contains
> BUGFLAG_WARNING:
>
> #define BUGFLAG_TAINT(taint) (BUGFLAG_WARNING | ((taint) << 8))
>
> But that was removed in f26dee15103f ("debug: Avoid setting
> BUGFLAG_WARNING twice"). So I think the Fixes: tag should point at that
> commit.

Ah, you're right. Should I repost the patch with the updated "fixes:" clause?


>
> cheers
>
>> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
>> index f2c562a0a427..0151af6c2a50 100644
>> --- a/arch/powerpc/include/asm/bug.h
>> +++ b/arch/powerpc/include/asm/bug.h
>> @@ -104,7 +104,7 @@
>>   "1: "PPC_TLNEI" %4,0\n" \
>>   _EMIT_BUG_ENTRY \
>>   : : "i" (__FILE__), "i" (__LINE__), \
>> -  "i" (BUGFLAG_TAINT(TAINT_WARN)), \
>> +  "i" (BUGFLAG_WARNING|BUGFLAG_TAINT(TAINT_WARN)),\
>>    "i" (sizeof(struct bug_entry)), \
>>    "r" (__ret_warn_on)); \
>>   } \
>> --
>> 2.11.0


--
Alexey
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Re: [PATCH kernel] powerpc/debug: Add missing warn flag to WARN_ON's non-builtin path

Michael Ellerman-2
Alexey Kardashevskiy <[hidden email]> writes:

> On 14/06/17 21:04, Michael Ellerman wrote:
>> Alexey Kardashevskiy <[hidden email]> writes:
>>
>>> When trapped on WARN_ON(), report_bug() is expected to return
>>> BUG_TRAP_TYPE_WARN so the caller could increment NIP by 4 and continue.
>>> The __builtin_constant_p() path of the PPC's WARN_ON() calls (indirectly)
>>> __WARN_FLAGS() which has BUGFLAG_WARNING set, however the other branch
>>> does not which makes report_bug() report a bug rather than a warning.
>>>
>>> Fixes: 19d436268dde95389 ("debug: Add _ONCE() logic to report_bug()")
>>> Signed-off-by: Alexey Kardashevskiy <[hidden email]>
>>> ---
>>>
>>> Actually 19d436268dde95389 replaced __WARN_TAINT() with __WARN_FLAGS()
>>> and lost BUGFLAG_TAINT() and this is not in the commit log so it is
>>> unclear:
>>> 1) why
>>
>> I think the rename is because previously the argument was a taint value,
>> whereas now it is a flags value (which is a superset of taint).
>>
>>> 2) whether this particular patch should be doing
>>>    BUGFLAG_WARNING|BUGFLAG_TAINT(TAINT_WARN)
>>>  or
>>>    BUGFLAG_WARNING|(flags)
>>
>> There is no flags here so the latter won't work AFAICS.
>>
>>> Any ideas? Thanks.
>>
>> Your patch looks correct to me. I assume it works?
>
> Yes, it does.

Thanks.

>> The bug isn't introduced by 19d436268dde ("debug: Add _ONCE() logic to
>> report_bug()") as far as I can see.
>>
>> If you check out that revision you see that BUGFLAG_TAINT still contains
>> BUGFLAG_WARNING:
>>
>> #define BUGFLAG_TAINT(taint) (BUGFLAG_WARNING | ((taint) << 8))
>>
>> But that was removed in f26dee15103f ("debug: Avoid setting
>> BUGFLAG_WARNING twice"). So I think the Fixes: tag should point at that
>> commit.
>
> Ah, you're right. Should I repost the patch with the updated "fixes:" clause?

No that's fine I can update it.

cheers
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Re: [kernel] powerpc/debug: Add missing warn flag to WARN_ON's non-builtin path

Michael Ellerman-3
In reply to this post by Alexey Kardashevskiy
On Wed, 2017-06-14 at 03:01:25 UTC, Alexey Kardashevskiy wrote:
> When trapped on WARN_ON(), report_bug() is expected to return
> BUG_TRAP_TYPE_WARN so the caller could increment NIP by 4 and continue.
> The __builtin_constant_p() path of the PPC's WARN_ON() calls (indirectly)
> __WARN_FLAGS() which has BUGFLAG_WARNING set, however the other branch
> does not which makes report_bug() report a bug rather than a warning.
>
> Fixes: f26dee15103f ("debug: Avoid setting BUGFLAG_WARNING twice")
> Signed-off-by: Alexey Kardashevskiy <[hidden email]>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/a093c92dc7f96a15de98ec8cfe38e6

cheers