From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Steven Rostedt <rostedt@goodmis.org>,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Ingo Molnar <mingo@redhat.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Paul Mackerras <paulus@samba.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v1 07/22] powerpc/ftrace: Use patch_instruction() return directly
Date: Wed, 4 May 2022 12:01:49 +0000 [thread overview]
Message-ID: <b7e8ffec-e13f-a423-4baf-b13cb8b5ad41@csgroup.eu> (raw)
In-Reply-To: <20220418154418.72ccc00c@gandalf.local.home>
Le 18/04/2022 à 21:44, Steven Rostedt a écrit :
> On Mon, 18 Apr 2022 11:51:16 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>
>>> --- a/arch/powerpc/kernel/trace/ftrace.c
>>> +++ b/arch/powerpc/kernel/trace/ftrace.c
>>> @@ -78,10 +78,7 @@ ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_t new)
>>> }
>>>
>>> /* replace the text with the new text */
>>> - if (patch_instruction((u32 *)ip, new))
>>> - return -EPERM;
>>> -
>>> - return 0;
>>> + return patch_instruction((u32 *)ip, new);
>>
>> I think the reason we were returning -EPERM is so that ftrace_bug() can
>
> That is correct.
>
>> throw the right error message. That will change due to this patch,
>> though I'm not sure how much it matters. -EFAULT and -EPERM seem to
>> print almost the same error message.
>
> In these cases it helps to know the type of failure, as the way to debug it
> is different.
>
> -EFAULT: It failed to read it the location. This means that the memory is
> likely not even mapped in, or the pointer is way off.
>
> -EINVAL: Means that what was read did not match what was expected (the code
> was already updated, pointing to the wrong location, or simply the
> calculation of what to expect is incorrect).
>
> -EPERM: Means the write failed. What was read was expected, but the
> permissions to write have not been updated properly.
>
> Differentiating the three is crucial to looking at where the issue lies
> when an ftrace_bug() triggers.
>
Apparently no caller really care about the value returned by
patch_instruction(), the ones who check the return value just check that
it's not 0.
So the most performant would be to have patch_instruction() return
-EPERM instead of -EFAULT in case of failure.
Christophe
next prev parent reply other threads:[~2022-05-04 12:01 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-24 14:29 [PATCH v1 00/22] powerpc: ftrace optimisation and cleanup and more [v1] Christophe Leroy
2022-03-24 14:29 ` [PATCH v1 01/22] powerpc/ftrace: Refactor prepare_ftrace_return() Christophe Leroy
2022-03-24 14:29 ` [PATCH v1 02/22] powerpc/ftrace: Remove redundant create_branch() calls Christophe Leroy
2022-03-24 14:29 ` [PATCH v1 03/22] powerpc/code-patching: Inline is_offset_in_{cond}_branch_range() Christophe Leroy
2022-03-24 14:29 ` [PATCH v1 04/22] powerpc/ftrace: Use is_offset_in_branch_range() Christophe Leroy
2022-03-24 14:29 ` [PATCH v1 05/22] powerpc/code-patching: Inline create_branch() Christophe Leroy
2022-03-24 14:29 ` [PATCH v1 06/22] powerpc/ftrace: Inline ftrace_modify_code() Christophe Leroy
2022-04-18 6:07 ` Naveen N. Rao
2022-04-22 9:12 ` Michael Ellerman
2022-05-04 11:43 ` Christophe Leroy
2022-03-24 14:29 ` [PATCH v1 07/22] powerpc/ftrace: Use patch_instruction() return directly Christophe Leroy
2022-04-18 6:21 ` Naveen N. Rao
2022-04-18 19:44 ` Steven Rostedt
2022-05-04 12:01 ` Christophe Leroy [this message]
2022-03-24 14:29 ` [PATCH v1 08/22] powerpc/ftrace: Make __ftrace_make_{nop/call}() common to PPC32 and PPC64 Christophe Leroy
2022-04-18 6:40 ` Naveen N. Rao
2022-05-04 12:19 ` Christophe Leroy
2022-05-06 11:41 ` Christophe Leroy
2022-03-24 14:29 ` [PATCH v1 09/22] powerpc/ftrace: Don't include ftrace.o for CONFIG_FTRACE_SYSCALLS Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 10/22] powerpc/ftrace: Use CONFIG_FUNCTION_TRACER instead of CONFIG_DYNAMIC_FTRACE Christophe Leroy
2022-04-18 7:00 ` Naveen N. Rao
2022-05-06 11:41 ` Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 11/22] powerpc/ftrace: Remove ftrace_plt_tramps[] Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 12/22] powerpc/ftrace: Use BRANCH_SET_LINK instead of value 1 Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 13/22] powerpc/ftrace: Use PPC_RAW_xxx() macros instead of opencoding Christophe Leroy
2022-04-18 7:38 ` Naveen N. Rao
2022-05-04 12:39 ` Christophe Leroy
2022-05-05 16:47 ` Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 14/22] powerpc/ftrace: Use size macro " Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 15/22] powerpc/ftrace: Simplify expected_nop_sequence() Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 16/22] powerpc/ftrace: Minimise number of #ifdefs Christophe Leroy
2022-04-18 7:59 ` Naveen N. Rao
2022-05-04 12:44 ` Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 17/22] powerpc/inst: Add __copy_inst_from_kernel_nofault() Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 18/22] powerpc/ftrace: Don't use copy_from_kernel_nofault() in module_trampoline_target() Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 19/22] powerpc/inst: Remove PPC_INST_BRANCH Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 20/22] powerpc/modules: Use PPC_INST_BRANCH_MASK instead of opencoding Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 21/22] powerpc/inst: Remove PPC_INST_BL Christophe Leroy
2022-03-24 14:30 ` [PATCH v1 22/22] powerpc/opcodes: Remove unused PPC_INST_XXX macros Christophe Leroy
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