linux-kernel - Re: [PATCH] Fix atomicity of TIF update in flush_thread() for x86

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Message-ID: <20070309022208.GB8387@Krystal>
Date:	Thu, 8 Mar 2007 21:22:08 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	David Miller <davem@...emloft.net>
Cc:	akpm@...ux-foundation.org, rschultz@...gle.com, ak@...e.de,
	mbligh@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix atomicity of TIF update in flush_thread() for x86_64

* David Miller (davem@...emloft.net) wrote:
> From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> Date: Thu, 8 Mar 2007 21:15:53 -0500
> 
> > Fix atomicity of TIF update in flush_thread() for x86_64
> > 
> > Race :
> > 
> > parent process executing :
> > sys_ptrace()
> >  (lock_kernel())
> >  (ptrace_get_task_struct(pid))
> >  arch_ptrace()
> >    ptrace_detach()
> >      ptrace_disable(child);
> >        clear_singlestep(child);
> >          clear_tsk_thread_flag(child, TIF_SINGLESTEP);
> >          (which clears the TIF_SINGLESTEP flag atomically from a different
> > 	  process)
> >  (put_task_struct(child))
> >  (unlock_kernel())
> > 
> > And at the same time, in the child process :
> > sys_execve()
> >  do_execve()
> >    search_binary_handler()
> >      load_elf_binary()
> >        flush_old_exec()
> >          flush_thread()
> >            doing a non-atomic thread flag update 
> > 
> > It applies on 2.6.20.
> > 
> > Signed-off-by: Rebecca Schultz <rschultz@...gle.com>
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> 
> Please fix all platforms, not just your favorite one, kthx.
> :-)

Please be comprehensive of the speed at which fingers can type on my
keyboard. Your quickness at replying to email is impressive though ;)

I am working on it, it won't take long.

Regards,

Mathieu

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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