linux-kernel - Re: [PATCH 2/3] ftrace: use struct pid

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20081205031736.GA5265@in.ibm.com>
Date:	Fri, 5 Dec 2008 08:47:36 +0530
From:	Dipankar Sarma <dipankar@...ibm.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <srostedt@...hat.com>,
	containers@...ts.osdl.org, Ingo Molnar <mingo@...e.hu>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/3] ftrace: use struct pid

On Thu, Dec 04, 2008 at 05:07:02AM -0800, Dave Hansen wrote:
> On Thu, 2008-12-04 at 04:56 -0800, Dave Hansen wrote:
> > On Thu, 2008-12-04 at 04:42 -0800, Eric W. Biederman wrote:
> > > 
> > > > +static void clear_ftrace_pid_task(struct pid **pid)
> > > > +{
> > > > +     struct task_struct *p;
> > > > +
> > >         rcu_read_lock();
> > > 
> > > > +     do_each_pid_task(*pid, PIDTYPE_PID, p) {
> > > > +             clear_tsk_trace_trace(p);
> > > > +     } while_each_pid_task(*pid, PIDTYPE_PID, p);
> > >         rcu_read_unlock()
> > > 
> > > > +     put_pid(*pid);
> > > > +
> > > > +     *pid = NULL;
> > > > +}
> > 
> > Could we get away with sticking the rcu_read_{un}lock() inside those
> > macros?  Those are going to get used in pretty high level code and we're
> > allowed to nest rcu_read_lock().  No danger of deadlocks or lock
> > inversions.
> 
> Why don't any of the other users of do_each_pid_task() use
> rcu_read_lock()?  They all seem to be under read_lock(&tasklist_lock)
> (except one is under a write lock of the same).

The pid hash list is protected by tasklist_lock, right ? If so,
holding read_lock(&tasklist_lock) will make this safe, you don't
need rcu_read_lock/unlock(). This isn't a lock-free reader.

Thanks
Dipankar
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/