Messages in this thread | | | Date | Thu, 10 Apr 2014 16:46:55 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH RESEND 2/2] tracing: syscall_regfunc() should not skip kernel threads |
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On 04/10, Steven Rostedt wrote: > > On Thu, 10 Apr 2014 15:38:55 +0200 > Oleg Nesterov <oleg@redhat.com> wrote: > > > > > 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. > > > > > > What about doing the set there? That is, we could add a check in the > > > call_userspacehelper() just before it does the do_execve, that if > > > sys_tracepoint_refcount is set, we set the TIF flag. > > > > But for what? > > Isn't call_usermodehelper() the reason you added this?
Sure. I meant, why complicate ____call_usermodehelper() and keep the unnecessary complication (PF_KTHREAD check( in syscall_*regfunc() ?
> > And if we do this, ____call_usermodehelper() needs write_lock_irq(tasklist) > > to serialize with syscall_*regfunc(). > > You mean for the slight race between checking if its set and when the > tracepoint is actually activated?
Or deactivated.
> I don't think we really care about that race.
OK, I won't argue. I agree, the problem is minor, but in this case imho it is better to do nothing than add the racy fix.
> I mean, the tracepoint is > activated usually by humans, and if they enabled it just as a usermode > helper is activated, and those are really fast to run, do we even care > if it is missed?
A user space task spawned by call_usermodehelper() can do everything, it can run forever.
> Now, if tracing is on and we need to set the flag, that should take the > task list lock to make sure that we don't miss clearing it. Missing the > set isn't a big deal, but missing the clearing of the flag is. > > void tracepoint_check_syscalls(void) > { > if (!sys_tracepoint_refcount) > return; > > read_lock(&tasklist_lock); > /* Make sure it wasn't cleared since taking the lock */ > if (sys_tracepoint_refcount) > set_tsk_thread_flag(current, TIF_SYSCALL_TRACEPOINT); > read_unlock(&tasklist_lock); > }
And how this can help to avoid the race? We need write_lock_irq().
Perhaps I missed something... and I simply do not understand why do you want to do this.
Oleg.
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