Messages in this thread | | | Date | Fri, 5 Dec 2008 08:47:36 +0530 | From | Dipankar Sarma <> | Subject | Re: [PATCH 2/3] ftrace: use struct pid |
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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
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