Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit d5671f6b authored by Denys Vlasenko's avatar Denys Vlasenko Committed by Paul E. McKenney
Browse files

rcu: Deinline rcu_read_lock_sched_held() if DEBUG_LOCK_ALLOC 

DEBUG_LOCK_ALLOC=y is not a production setting, but it is
not very unusual either. Many developers routinely
use kernels built with it enabled.

Apart from being selected by hand, it is also auto-selected by
PROVE_LOCKING "Lock debugging: prove locking correctness" and
LOCK_STAT "Lock usage statistics" config options.
LOCK STAT is necessary for "perf lock" to work.

I wouldn't spend too much time optimizing it, but this particular
function has a very large cost in code size: when it is deinlined,
code size decreases by 830,000 bytes:

    text     data      bss       dec     hex filename
85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
84837612 22294424 20627456 127759492 79d7484 vmlinux

(with this config: http://busybox.net/~vda/kernel_config

)

Signed-off-by: default avatarDenys Vlasenko <dvlasenk@redhat.com>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Lai Jiangshan <laijs@cn.fujitsu.com>
CC: Tejun Heo <tj@kernel.org>
CC: Oleg Nesterov <oleg@redhat.com>
CC: linux-kernel@vger.kernel.org
Reviewed-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent d1ec4c34

include/linux/rcupdate.h

+2 −38
Original line number Diff line number Diff line
@@ -469,46 +469,10 @@ int rcu_read_lock_bh_held(void); 
 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an

 * RCU-sched read-side critical section.  In absence of

 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side

 * critical section unless it can prove otherwise.  Note that disabling

 * of preemption (including disabling irqs) counts as an RCU-sched

 * read-side critical section.  This is useful for debug checks in functions

 * that required that they be called within an RCU-sched read-side

 * critical section.

 *

 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot

 * and while lockdep is disabled.

 *

 * Note that if the CPU is in the idle loop from an RCU point of

 * view (ie: that we are in the section between rcu_idle_enter() and

 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU

 * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs

 * that are in such a section, considering these as in extended quiescent

 * state, so such a CPU is effectively never in an RCU read-side critical

 * section regardless of what RCU primitives it invokes.  This state of

 * affairs is required --- we need to keep an RCU-free window in idle

 * where the CPU may possibly enter into low power mode. This way we can

 * notice an extended quiescent state to other CPUs that started a grace

 * period. Otherwise we would delay any grace period as long as we run in

 * the idle task.

 *

 * Similarly, we avoid claiming an SRCU read lock held if the current

 * CPU is offline.

 * critical section unless it can prove otherwise.

 */

#ifdef CONFIG_PREEMPT_COUNT

static inline int rcu_read_lock_sched_held(void)

{

	int lockdep_opinion = 0;



	if (!debug_lockdep_rcu_enabled())

		return 1;

	if (!rcu_is_watching())

		return 0;

	if (!rcu_lockdep_current_cpu_online())

		return 0;

	if (debug_locks)

		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);

	return lockdep_opinion || preempt_count() != 0 || irqs_disabled();

}

int rcu_read_lock_sched_held(void);

#else /* #ifdef CONFIG_PREEMPT_COUNT */

static inline int rcu_read_lock_sched_held(void)

{

kernel/rcu/update.c

+49 −0
Original line number Diff line number Diff line
@@ -62,6 +62,55 @@ MODULE_ALIAS("rcupdate"); 


module_param(rcu_expedited, int, 0);



#if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT)

/**

 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?

 *

 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an

 * RCU-sched read-side critical section.  In absence of

 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side

 * critical section unless it can prove otherwise.  Note that disabling

 * of preemption (including disabling irqs) counts as an RCU-sched

 * read-side critical section.  This is useful for debug checks in functions

 * that required that they be called within an RCU-sched read-side

 * critical section.

 *

 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot

 * and while lockdep is disabled.

 *

 * Note that if the CPU is in the idle loop from an RCU point of

 * view (ie: that we are in the section between rcu_idle_enter() and

 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU

 * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs

 * that are in such a section, considering these as in extended quiescent

 * state, so such a CPU is effectively never in an RCU read-side critical

 * section regardless of what RCU primitives it invokes.  This state of

 * affairs is required --- we need to keep an RCU-free window in idle

 * where the CPU may possibly enter into low power mode. This way we can

 * notice an extended quiescent state to other CPUs that started a grace

 * period. Otherwise we would delay any grace period as long as we run in

 * the idle task.

 *

 * Similarly, we avoid claiming an SRCU read lock held if the current

 * CPU is offline.

 */

int rcu_read_lock_sched_held(void)

{

	int lockdep_opinion = 0;



	if (!debug_lockdep_rcu_enabled())

		return 1;

	if (!rcu_is_watching())

		return 0;

	if (!rcu_lockdep_current_cpu_online())

		return 0;

	if (debug_locks)

		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);

	return lockdep_opinion || preempt_count() != 0 || irqs_disabled();

}

EXPORT_SYMBOL(rcu_read_lock_sched_held);

#endif



#ifndef CONFIG_TINY_RCU



static atomic_t rcu_expedited_nesting =