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

[Josh Poimboeuf <jpoimboe@kernel.org>]

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@huaweicloud.com>
> > 
> > Thanks!
> > 
> > Acked-by: Josh Poimboeuf <jpoimboe@kernel.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