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Commit 49b550fe authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

Pull RCU fixes from Ingo Molnar:
 "This fixes sporadic ACPI related hangs in synchronize_rcu() that were
  caused by the ACPI code mistakenly relying on an aspect of RCU that
  was neither promised to work nor reliable but which happened to work -
  until in v4.9 we changed the RCU implementation, which made the hangs
  more prominent.

  Since the mis-use of the RCU facility wasn't properly detected and
  prevented either, these fixes make the RCU side work reliably instead
  of working around the problem in the ACPI code.

  Hence the slightly larger diffstat that goes beyond the normal scope
  of RCU fixes in -rc kernels"

* 'rcu-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rcu: Narrow early boot window of illegal synchronous grace periods
  rcu: Remove cond_resched() from Tiny synchronize_sched()
parents 9da96f99 3e4f7a49

include/linux/rcupdate.h

+4 −0
Original line number Diff line number Diff line
@@ -444,6 +444,10 @@ bool __rcu_is_watching(void); 
#error "Unknown RCU implementation specified to kernel configuration"

#endif



#define RCU_SCHEDULER_INACTIVE	0

#define RCU_SCHEDULER_INIT	1

#define RCU_SCHEDULER_RUNNING	2



/*

 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic

 * initialization and destruction of rcu_head on the stack. rcu_head structures

kernel/rcu/rcu.h

+1 −0
Original line number Diff line number Diff line
@@ -136,6 +136,7 @@ int rcu_jiffies_till_stall_check(void); 
#define TPS(x)  tracepoint_string(x)



void rcu_early_boot_tests(void);

void rcu_test_sync_prims(void);



/*

 * This function really isn't for public consumption, but RCU is special in

kernel/rcu/tiny.c

+0 −4
Original line number Diff line number Diff line
@@ -185,9 +185,6 @@ static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused 
 * benefits of doing might_sleep() to reduce latency.)

 *

 * Cool, huh?  (Due to Josh Triplett.)

 *

 * But we want to make this a static inline later.  The cond_resched()

 * currently makes this problematic.

 */

void synchronize_sched(void)

{
@@ -195,7 +192,6 @@ void synchronize_sched(void) 
			 lock_is_held(&rcu_lock_map) ||

			 lock_is_held(&rcu_sched_lock_map),

			 "Illegal synchronize_sched() in RCU read-side critical section");

	cond_resched();

}

EXPORT_SYMBOL_GPL(synchronize_sched);

kernel/rcu/tiny_plugin.h

+7 −2
Original line number Diff line number Diff line
@@ -60,12 +60,17 @@ EXPORT_SYMBOL_GPL(rcu_scheduler_active); 


/*

 * During boot, we forgive RCU lockdep issues.  After this function is

 * invoked, we start taking RCU lockdep issues seriously.

 * invoked, we start taking RCU lockdep issues seriously.  Note that unlike

 * Tree RCU, Tiny RCU transitions directly from RCU_SCHEDULER_INACTIVE

 * to RCU_SCHEDULER_RUNNING, skipping the RCU_SCHEDULER_INIT stage.

 * The reason for this is that Tiny RCU does not need kthreads, so does

 * not have to care about the fact that the scheduler is half-initialized

 * at a certain phase of the boot process.

 */

void __init rcu_scheduler_starting(void)

{

	WARN_ON(nr_context_switches() > 0);

	rcu_scheduler_active = 1;

	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;

}



#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

kernel/rcu/tree.c

+20 −13
Original line number Diff line number Diff line
@@ -127,13 +127,16 @@ int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ 
int sysctl_panic_on_rcu_stall __read_mostly;



/*

 * The rcu_scheduler_active variable transitions from zero to one just

 * before the first task is spawned.  So when this variable is zero, RCU

 * can assume that there is but one task, allowing RCU to (for example)

 * The rcu_scheduler_active variable is initialized to the value

 * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the

 * first task is spawned.  So when this variable is RCU_SCHEDULER_INACTIVE,

 * RCU can assume that there is but one task, allowing RCU to (for example)

 * optimize synchronize_rcu() to a simple barrier().  When this variable

 * is one, RCU must actually do all the hard work required to detect real

 * grace periods.  This variable is also used to suppress boot-time false

 * positives from lockdep-RCU error checking.

 * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required

 * to detect real grace periods.  This variable is also used to suppress

 * boot-time false positives from lockdep-RCU error checking.  Finally, it

 * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU

 * is fully initialized, including all of its kthreads having been spawned.

 */

int rcu_scheduler_active __read_mostly;

EXPORT_SYMBOL_GPL(rcu_scheduler_active);
@@ -3980,18 +3983,22 @@ static int __init rcu_spawn_gp_kthread(void) 
early_initcall(rcu_spawn_gp_kthread);



/*

 * This function is invoked towards the end of the scheduler's initialization

 * process.  Before this is called, the idle task might contain

 * RCU read-side critical sections (during which time, this idle

 * task is booting the system).  After this function is called, the

 * idle tasks are prohibited from containing RCU read-side critical

 * sections.  This function also enables RCU lockdep checking.

 * This function is invoked towards the end of the scheduler's

 * initialization process.  Before this is called, the idle task might

 * contain synchronous grace-period primitives (during which time, this idle

 * task is booting the system, and such primitives are no-ops).  After this

 * function is called, any synchronous grace-period primitives are run as

 * expedited, with the requesting task driving the grace period forward.

 * A later core_initcall() rcu_exp_runtime_mode() will switch to full

 * runtime RCU functionality.

 */

void rcu_scheduler_starting(void)

{

	WARN_ON(num_online_cpus() != 1);

	WARN_ON(nr_context_switches() > 0);

	rcu_scheduler_active = 1;

	rcu_test_sync_prims();

	rcu_scheduler_active = RCU_SCHEDULER_INIT;

	rcu_test_sync_prims();

}



/*