Messages in this thread Patch in this message | | | Date | Fri, 27 Apr 2018 09:44:16 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing with preempt on |
| |
On Fri, Apr 27, 2018 at 12:13:30PM -0400, Steven Rostedt wrote: > On Fri, 27 Apr 2018 08:57:01 -0700 > "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote: > > > > + if (preempt_on) { \ > > > + WARN_ON_ONCE(in_nmi()); /* no srcu from nmi */ \ > > > > Very good on this check, thank you! > > I think you need to return and not call the read lock.
Works for me either way, at least assuming that the splat actually gets printed. ;-)
> if (WARN_ON_ONCE(in_nmi())) > return; > > > > > > + idx = srcu_read_lock(&tracepoint_srcu); \ > > > > Hmmm... Do I need to create a _notrace variant of srcu_read_lock() > > and srcu_read_unlock()? > > I think so.
OK, please see the (untested) patch below. Of course, srcu_read_lock_notrace() invokes __srcu_read_lock(), which looks as follows:
int __srcu_read_lock(struct srcu_struct *sp) { int idx;
idx = READ_ONCE(sp->srcu_idx) & 0x1; this_cpu_inc(sp->sda->srcu_lock_count[idx]); smp_mb(); /* B */ /* Avoid leaking the critical section. */ return idx; }
Do I also need to make a notrace version of __srcu_read_lock()? Same question for __srcu_read_unlock(), which is similar. If so, assuming that there is no need for a notrace variant of this_cpu_inc() and smp_mb(), I suppose I could simply macro-ize the internals in both cases, but perhaps you have a better approach.
Thanx, Paul
------------------------------------------------------------------------
diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 91494d7e8e41..e2e2cf05a6eb 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -195,6 +195,16 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) return retval; } +/* Used by tracing, cannot be traced and cannot invoke lockdep. */ +static inline notrace int +srcu_read_lock_notrace(struct srcu_struct *sp) __acquires(sp) +{ + int retval; + + retval = __srcu_read_lock(sp); + return retval; +} + /** * srcu_read_unlock - unregister a old reader from an SRCU-protected structure. * @sp: srcu_struct in which to unregister the old reader. @@ -205,6 +215,13 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) static inline void srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp) { + __srcu_read_unlock(sp, idx); +} + +/* Used by tracing, cannot be traced and cannot call lockdep. */ +static inline notrace void +srcu_read_unlock_notrace(struct srcu_struct *sp, int idx) __releases(sp) +{ rcu_lock_release(&(sp)->dep_map); __srcu_read_unlock(sp, idx); }
| |