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Commit 131906b0062ddde7f85bbe67754983c754648bd8

Authored by Paul E. McKenney
1 parent b0d304172f
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

rcu: decrease rcu_report_exp_rnp coupling with scheduler 

PREEMPT_RCU read-side critical sections blocking an expedited grace
period invoke rcu_report_exp_rnp().  When the last such critical section
has completed, rcu_report_exp_rnp() invokes the scheduler to wake up the
task that invoked synchronize_rcu_expedited() -- needlessly holding the
root rcu_node structure's lock while doing so, thus needlessly providing
a way for RCU and the scheduler to deadlock.

This commit therefore releases the root rcu_node structure's lock before
calling wake_up().

Reported-by: Ed Tomlinson <edt@aei.ca>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Showing 1 changed file with 4 additions and 2 deletions Side-by-side Diff

kernel/rcutree_plugin.h
Diff comments   View file @ 131906b
... ... @@ -695,9 +695,12 @@
695 695  
696 696 raw_spin_lock_irqsave(&rnp->lock, flags);
697 697 for (;;) {
698   - if (!sync_rcu_preempt_exp_done(rnp))
  698 + if (!sync_rcu_preempt_exp_done(rnp)) {
  699 + raw_spin_unlock_irqrestore(&rnp->lock, flags);
699 700 break;
  701 + }
700 702 if (rnp->parent == NULL) {
  703 + raw_spin_unlock_irqrestore(&rnp->lock, flags);
701 704 wake_up(&sync_rcu_preempt_exp_wq);
702 705 break;
703 706 }
... ... @@ -707,7 +710,6 @@
707 710 raw_spin_lock(&rnp->lock); /* irqs already disabled */
708 711 rnp->expmask &= ~mask;
709 712 }
710   - raw_spin_unlock_irqrestore(&rnp->lock, flags);
711 713 }
712 714  
713 715 /*