lkml.org 
[lkml]   [2012]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: lots of suspicious RCU traces
On (10/24/12 12:41), Paul E. McKenney wrote:
> On Wed, Oct 24, 2012 at 12:17:16PM -0700, Sergey Senozhatsky wrote:
> > On (10/24/12 20:52), Oleg Nesterov wrote:
> > > On 10/24, Sergey Senozhatsky wrote:
> > > >
> > > > On (10/24/12 20:06), Oleg Nesterov wrote:
> > > > > On 10/24, Sergey Senozhatsky wrote:
> > > > > >
> > > > > > small question,
> > > > > >
> > > > > > ptrace_notify() and forward calls are able to both indirectly and directly call schedule(),
> > > > > > /* direct call from ptrace_stop()*/,
> > > > > > should, in this case, rcu_user_enter() be called before tracehook_report_syscall_exit(regs, step)
> > > > > > and ptrace chain?
> > > > >
> > > > > Well, I don't really understand this magic... but why?
> > > > >
> > > >
> > > > My understanding is (I may be wrong)
> > >
> > > Oh, I bet I have much more chances to be wrong ;)
> > >
> > > > that we can schedule() from ptrace chain to
> > >
> > > I don't understand how ptrace chain differs from, say, audit_syscall_exit().
> > > There is nothing special in ptrace_stop() in this respect.
> > >
> >
> > hm.
> >
> > > > some arbitrary task, which will continue its execution from the point where RCU assumes
> > > > CPU as not idle, while CPU in fact still in idle state -- no one said rcu_idle_exit()
> > >
> > > confused... of course it would be wrong if syscall_trace_leave() is
> > > called when CPU is considered idle,
> > >
> >
> > sorry, I meant idle from RCU point of view:
> >
> > int rcu_is_cpu_idle(void)
> > {
> > return !rcu_dynticks_nesting;
> > }
>
> Hmmm... This reproduces on UP builds, then?
>

I'll compile UP build (will offlining of N-1 CPUs do the trick?).

-ss

> > > > if so, does the same apply to in_user?
> > >
> > > Not sure we understand each other. But I believe that ->in_user should be
> > > already false when syscall_trace_leave() is called.
> >
> > oh, my apology. I was very wrong about this.
>
> Frederic, thoughts?
>
> Thanx, Paul
>


\
 
 \ /
  Last update: 2012-10-27 10:01    [W:0.107 / U:1.112 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site