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Commit cb7e9704 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'rcu/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu 

Pull RCU fixes from Paul McKenney:
 "I must confess that this past merge window was not RCU's best showing.
  This series contains three more fixes for RCU regressions:

   1.   A fix to __DECLARE_TRACE_RCU() that causes it to act as an
        interrupt from idle rather than as a task switch from idle.
        This change is needed due to the recent use of _rcuidle()
        tracepoints that can be invoked from interrupt handlers as well
        as from idle.  Without this fix, invoking _rcuidle() tracepoints
        from interrupt handlers results in splats and (more seriously)
        confusion on RCU's part as to whether a given CPU is idle or not.
        This confusion can in turn result in too-short grace periods and
        therefore random memory corruption.

   2.   A fix to a subtle deadlock that could result due to RCU doing
        a wakeup while holding one of its rcu_node structure's locks.
        Although the probability of occurrence is low, it really
        does happen.  The fix, courtesy of Steven Rostedt, uses
        irq_work_queue() to avoid the deadlock.

   3.   A fix to a silent deadlock (invisible to lockdep) due to the
        interaction of timeouts posted by RCU debug code enabled by
        CONFIG_PROVE_RCU_DELAY=y, grace-period initialization, and CPU
        hotplug operations.  This will not occur in production kernels,
        but really does occur in randconfig testing.  Diagnosis courtesy
        of Steven Rostedt"

* 'rcu/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  rcu: Fix deadlock with CPU hotplug, RCU GP init, and timer migration
  rcu: Don't call wakeup() with rcu_node structure ->lock held
  trace: Allow idle-safe tracepoints to be called from irq
parents dcae7f2d 971394f3

include/linux/tracepoint.h

+2 −2
Original line number Diff line number Diff line
@@ -145,8 +145,8 @@ static inline void tracepoint_synchronize_unregister(void) 
				TP_PROTO(data_proto),			\

				TP_ARGS(data_args),			\

				TP_CONDITION(cond),			\

				rcu_idle_exit(),			\

				rcu_idle_enter());			\

				rcu_irq_enter(),			\

				rcu_irq_exit());			\

	}

#else

#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)

init/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -431,6 +431,7 @@ choice 
config TREE_RCU

	bool "Tree-based hierarchical RCU"

	depends on !PREEMPT && SMP

	select IRQ_WORK

	help

	  This option selects the RCU implementation that is

	  designed for very large SMP system with hundreds or

kernel/rcutree.c

+17 −4
Original line number Diff line number Diff line
@@ -1451,9 +1451,9 @@ static int rcu_gp_init(struct rcu_state *rsp) 
					    rnp->grphi, rnp->qsmask);

		raw_spin_unlock_irq(&rnp->lock);

#ifdef CONFIG_PROVE_RCU_DELAY

		if ((prandom_u32() % (rcu_num_nodes * 8)) == 0 &&

		if ((prandom_u32() % (rcu_num_nodes + 1)) == 0 &&

		    system_state == SYSTEM_RUNNING)

			schedule_timeout_uninterruptible(2);

			udelay(200);

#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */

		cond_resched();

	}
@@ -1613,6 +1613,14 @@ static int __noreturn rcu_gp_kthread(void *arg) 
	}

}



static void rsp_wakeup(struct irq_work *work)

{

	struct rcu_state *rsp = container_of(work, struct rcu_state, wakeup_work);



	/* Wake up rcu_gp_kthread() to start the grace period. */

	wake_up(&rsp->gp_wq);

}



/*

 * Start a new RCU grace period if warranted, re-initializing the hierarchy

 * in preparation for detecting the next grace period.  The caller must hold
@@ -1637,8 +1645,12 @@ rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, 
	}

	rsp->gp_flags = RCU_GP_FLAG_INIT;



	/* Wake up rcu_gp_kthread() to start the grace period. */

	wake_up(&rsp->gp_wq);

	/*

	 * We can't do wakeups while holding the rnp->lock, as that

	 * could cause possible deadlocks with the rq->lock. Deter

	 * the wakeup to interrupt context.

	 */

	irq_work_queue(&rsp->wakeup_work);

}



/*
@@ -3235,6 +3247,7 @@ static void __init rcu_init_one(struct rcu_state *rsp, 


	rsp->rda = rda;

	init_waitqueue_head(&rsp->gp_wq);

	init_irq_work(&rsp->wakeup_work, rsp_wakeup);

	rnp = rsp->level[rcu_num_lvls - 1];

	for_each_possible_cpu(i) {

		while (i > rnp->grphi)

kernel/rcutree.h

+2 −0
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ 
#include <linux/threads.h>

#include <linux/cpumask.h>

#include <linux/seqlock.h>

#include <linux/irq_work.h>



/*

 * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
@@ -442,6 +443,7 @@ struct rcu_state { 
	char *name;				/* Name of structure. */

	char abbr;				/* Abbreviated name. */

	struct list_head flavors;		/* List of RCU flavors. */

	struct irq_work wakeup_work;		/* Postponed wakeups */

};



/* Values for rcu_state structure's gp_flags field. */