linux-kernel - Re: [PATCH] x86/unwind/orc: Fix unwind for newly forked tasks

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Message-ID: <afae0e1f-7033-858c-ea5d-2b4a5383e9c6@huaweicloud.com>
Date: Fri, 11 Oct 2024 14:50:32 +0800
From: Zheng Yejian <zhengyejian@...weicloud.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, brgerst@...il.com,
 samitolvanen@...gle.com, kees@...nel.org, x86@...nel.org,
 linux-kernel@...r.kernel.org, Ye Weihua <yeweihua4@...wei.com>
Subject: Re: [PATCH] x86/unwind/orc: Fix unwind for newly forked tasks

On 2024/9/14 07:11, Josh Poimboeuf wrote:
> On Fri, Sep 13, 2024 at 10:45:01AM +0800, Zheng Yejian wrote:
>> When arch_stack_walk_reliable() is called to unwind for newly forked
>> tasks, the return value is negative which means the call stack is
>> unreliable. This obviously does not meet expectations.
>>
>> The root cause is that after commit 3aec4ecb3d1f ("x86: Rewrite
>>   ret_from_fork() in C"), the 'ret_addr' of newly forked task is changed
>> to 'ret_from_fork_asm' (see copy_thread()), then at the start of the
>> unwind, it is incorrectly interprets not as a "signal" one because
>> 'ret_from_fork' is still used to determine the initial "signal" (see
>> __unwind_start()). Then the address gets incorrectly decremented in the
>> call to orc_find() (see unwind_next_frame()) and resulting in the
>> incorrect ORC data.
>>
>> To fix it, check 'ret_from_fork_asm' rather than 'ret_from_fork' in
>> __unwind_start().
>>
>> Fixes: 3aec4ecb3d1f ("x86: Rewrite ret_from_fork() in C")
>> Signed-off-by: Zheng Yejian <zhengyejian@...weicloud.com>
> 
> Thanks!
> 
> Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
> 

Hi, Josh, thanks for your ack!
Will this patch go into mainline soon?

-- 
Thanks,
Zheng Yejian