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

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Message-ID: <20241011153938.knk2yp46ajjo27gj@treble>
Date: Fri, 11 Oct 2024 08:39:38 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Zheng Yejian <zhengyejian@...weicloud.com>
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 Fri, Oct 11, 2024 at 02:50:32PM +0800, Zheng Yejian wrote:
> 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?

Sorry about that, I'll go ahead and queue this up.

-- 
Josh