linux-kernel - Re: [PATCH 2/2] tracing: syscall_regfunc() should not skip kernel threads

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Date:	Sun, 17 Mar 2013 20:04:38 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 2/2] tracing: syscall_regfunc() should not skip kernel
	threads

On 03/17, Steven Rostedt wrote:
>
> On Sun, 2013-03-17 at 19:28 +0100, Oleg Nesterov wrote:
> > syscall_regfunc() ignores the kernel thread because "it has
> > no effect", see cc3b13c1 "Don't trace kernel thread syscalls".
> >
> > However, this means that a user-space task spawned by
> > call_usermodehelper() won't report the system calls if
> > kernel_execve() is called when sys_tracepoint_refcount != 0.
> >
> > Remove this check. Hopefully the unnecessary report from
> > ret_from_fork path mentioned by cc3b13c1 is fine. In fact
> > "this is the only case" is not true. Say, kernel_execve()
> > itself does "int 80" on X86_32. Hopefully fine too.
>
> I'm really thinking the TIF_SYSCALL_TRACEPOINT flag is getting a bit
> ridiculous. We really should have a "swap syscall table when tracepoints
> enabled" that changes the syscall table that does exactly the same thing
> as the normal table but wraps the system call with the tracepoints.

But we also need to force the slow path in system_call...

Anyway, do you agree with this change for now?

Oleg.

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