[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 1 Feb 2012 16:55:54 -0800
From: Josh Triplett <josh@...htriplett.org>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
dipankar@...ibm.com, akpm@...ux-foundation.org,
mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
fweisbec@...il.com, patches@...aro.org
Subject: Re: [PATCH RFC tip/core/rcu 03/41] rcu: Add lockdep-RCU checks for
simple self-deadlock
On Wed, Feb 01, 2012 at 11:41:21AM -0800, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
>
> It is illegal to have a grace period within a same-flavor RCU read-side
> critical section, so this commit adds lockdep-RCU checks to splat when
> such abuse is encountered. This commit does not detect more elaborate
> RCU deadlock situations. These situations might be a job for lockdep
> enhancements.
Since doing so also violates the prohibition on blocking within an RCU
read-side critical section, wouldn't it suffice to call might_sleep() or
equivalent, which also detects other problems? (Obviously this doesn't
apply to SRCU, but it applies to the other variants of RCU.)
> --- a/kernel/rcutiny.c
> +++ b/kernel/rcutiny.c
> @@ -319,6 +319,9 @@ static void rcu_process_callbacks(struct softirq_action *unused)
> */
> void synchronize_sched(void)
> {
> + rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
> + "Illegal grace period in RCU read-side "
> + "critical section");
This message doesn't seem entirely obvious to me. A grace period didn't
occur; a synchronize call did, which tried to request a grace period
that can never happen.
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1816,6 +1816,9 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
> */
> void synchronize_sched(void)
> {
> + rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
> + "Illegal synchronize_sched() in RCU-sched "
> + "read-side critical section");
> if (rcu_blocking_is_gp())
> return;
> wait_rcu_gp(call_rcu_sched);
> @@ -1833,6 +1836,9 @@ EXPORT_SYMBOL_GPL(synchronize_sched);
> */
> void synchronize_rcu_bh(void)
> {
> + rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
> + "Illegal synchronize_sched() in RCU-bh "
> + "read-side critical section");
Copy-paste problem here: this should say synchronize_sched_bh. (Or
perhaps it should say __func__. :) )
> --- a/kernel/srcu.c
> +++ b/kernel/srcu.c
> @@ -172,6 +172,10 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
> {
> int idx;
>
> + rcu_lockdep_assert(!lock_is_held(&sp->dep_map),
> + "Illegal SRCU grace period in same-type "
> + "SRCU read-side critical section");
Same issue with the message: a grace period didn't occur, and it never
will; a call to synchronize_srcu requesting a grace period occurred.
- Josh Triplett
--
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/
Powered by blists - more mailing lists