From: Paul E. McKenney Date: Tue, 29 Sep 2015 14:55:41 +0000 (-0700) Subject: rcu: Remove lock-acquisition loop from rcu_read_unlock_special() X-Git-Tag: v4.14-rc1~4092^2^2~1^3~10 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=8ba9153b2c3ab733d64e22adb57820ccb6afc496;p=platform%2Fkernel%2Flinux-rpi.git rcu: Remove lock-acquisition loop from rcu_read_unlock_special() Several releases have come and gone without the warning triggering, so remove the lock-acquisition loop. Retain the WARN_ON_ONCE() out of sheer paranoia. Signed-off-by: Paul E. McKenney --- diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 57ba873..ae4ce2b 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -449,19 +449,13 @@ void rcu_read_unlock_special(struct task_struct *t) /* * Remove this task from the list it blocked on. The task - * now remains queued on the rcu_node corresponding to - * the CPU it first blocked on, so the first attempt to - * acquire the task's rcu_node's ->lock will succeed. - * Keep the loop and add a WARN_ON() out of sheer paranoia. + * now remains queued on the rcu_node corresponding to the + * CPU it first blocked on, so there is no longer any need + * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia. */ - for (;;) { - rnp = t->rcu_blocked_node; - raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ - if (rnp == t->rcu_blocked_node) - break; - WARN_ON_ONCE(1); - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - } + rnp = t->rcu_blocked_node; + raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ + WARN_ON_ONCE(rnp != t->rcu_blocked_node); empty_norm = !rcu_preempt_blocked_readers_cgp(rnp); empty_exp = sync_rcu_preempt_exp_done(rnp); smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */