Messages in this thread Patch in this message | | | Date | Wed, 9 Apr 2014 18:40:41 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 2/5] tracepoint: Convert process iteration to use for_each_process_thread() |
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On Wed, Apr 09, 2014 at 04:28:35PM +0000, Mathieu Desnoyers wrote: > ----- Original Message ----- > > From: "Frederic Weisbecker" <fweisbec@gmail.com> > > To: "LKML" <linux-kernel@vger.kernel.org> > > Cc: "Frederic Weisbecker" <fweisbec@gmail.com>, "Andrew Morton" <akpm@linux-foundation.org>, "Ingo Molnar" > > <mingo@kernel.org>, "Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>, "Oleg Nesterov" <oleg@redhat.com>, "Steven > > Rostedt" <rostedt@goodmis.org> > > Sent: Wednesday, April 9, 2014 12:11:19 PM > > Subject: [PATCH 2/5] tracepoint: Convert process iteration to use for_each_process_thread() > > > > do_each_thread/while_each_thread iterators are deprecated by > > for_each_thread/for_each_process_thread() APIs. > > > > Lets convert the callers in the tracepoint code. The ultimate > > goal is to remove the struct task_struct::thread_group field and > > the corresponding do_each_thread/while_each_thread iterators that are > > RCU unsafe. > > > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: Ingo Molnar <mingo@kernel.org> > > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > Cc: Oleg Nesterov <oleg@redhat.com> > > Cc: Steven Rostedt <rostedt@goodmis.org> > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > > --- > > kernel/tracepoint.c | 12 ++++++------ > > 1 file changed, 6 insertions(+), 6 deletions(-) > > > > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c > > index fb0a38a..00a7e8b 100644 > > --- a/kernel/tracepoint.c > > +++ b/kernel/tracepoint.c > > @@ -561,15 +561,15 @@ static int sys_tracepoint_refcount; > > void syscall_regfunc(void) > > { > > unsigned long flags; > > - struct task_struct *g, *t; > > + struct task_struct *p, *t; > > > > if (!sys_tracepoint_refcount) { > > read_lock_irqsave(&tasklist_lock, flags); > > - do_each_thread(g, t) { > > + for_each_process_thread(p, t) { > > What are the locking rules for for_each_process_thread() ? > > Is it required to hold RCU read-side lock ? (it's not the case here) > > Is tasklist_lock read-side lock sufficient ?
It's the same requirements than do_each_thread while_each_thread: tasklist_lock or RCU. Except that it's really RCU-safe. while_each_thread isn't really safe due to issues with concurrent exec/de_thread()
Then it depends on your requirement, if you can tolerate concurrent adds and removals or not. Here tasklist_lock seems required or we may miss some tasks' syscall traces.
> > A quick glance at those for_each iterator defines in sched.h was not > helpful in finding this information.
Agreed, I'm going to add comments to precise that.
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