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Commit 9786cff3 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

Pull locking fixes from Ingo Molnar:
 "Spinlock performance regression fix, plus documentation fixes"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/static_keys: Fix up the static keys documentation
  locking/qspinlock/x86: Only emit the test-and-set fallback when building guest support
  locking/qspinlock/x86: Fix performance regression under unaccelerated VMs
  locking/static_keys: Fix a silly typo
parents 1b3dfde3 1975dbc2

Documentation/static-keys.txt

+2 −2
Original line number Diff line number Diff line
@@ -15,8 +15,8 @@ The updated API replacements are: 


DEFINE_STATIC_KEY_TRUE(key);

DEFINE_STATIC_KEY_FALSE(key);

static_key_likely()

statick_key_unlikely()

static_branch_likely()

static_branch_unlikely()



0) Abstract

arch/x86/include/asm/qspinlock.h

+14 −5
Original line number Diff line number Diff line
@@ -39,18 +39,27 @@ static inline void queued_spin_unlock(struct qspinlock *lock) 
}

#endif



#define virt_queued_spin_lock virt_queued_spin_lock



static inline bool virt_queued_spin_lock(struct qspinlock *lock)

#ifdef CONFIG_PARAVIRT

#define virt_spin_lock virt_spin_lock

static inline bool virt_spin_lock(struct qspinlock *lock)

{

	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))

		return false;



	while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0)

	/*

	 * On hypervisors without PARAVIRT_SPINLOCKS support we fall

	 * back to a Test-and-Set spinlock, because fair locks have

	 * horrible lock 'holder' preemption issues.

	 */



	do {

		while (atomic_read(&lock->val) != 0)

			cpu_relax();

	} while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);



	return true;

}

#endif /* CONFIG_PARAVIRT */



#include <asm-generic/qspinlock.h>

include/asm-generic/qspinlock.h

+2 −2
Original line number Diff line number Diff line
@@ -111,8 +111,8 @@ static inline void queued_spin_unlock_wait(struct qspinlock *lock) 
		cpu_relax();

}



#ifndef virt_queued_spin_lock

static __always_inline bool virt_queued_spin_lock(struct qspinlock *lock)

#ifndef virt_spin_lock

static __always_inline bool virt_spin_lock(struct qspinlock *lock)

{

	return false;

}

include/linux/jump_label.h

+4 −6
Original line number Diff line number Diff line
@@ -21,8 +21,8 @@ 
 *

 * DEFINE_STATIC_KEY_TRUE(key);

 * DEFINE_STATIC_KEY_FALSE(key);

 * static_key_likely()

 * statick_key_unlikely()

 * static_branch_likely()

 * static_branch_unlikely()

 *

 * Jump labels provide an interface to generate dynamic branches using

 * self-modifying code. Assuming toolchain and architecture support, if we
@@ -45,12 +45,10 @@ 
 * statement, setting the key to true requires us to patch in a jump

 * to the out-of-line of true branch.

 *

 * In addtion to static_branch_{enable,disable}, we can also reference count

 * In addition to static_branch_{enable,disable}, we can also reference count

 * the key or branch direction via static_branch_{inc,dec}. Thus,

 * static_branch_inc() can be thought of as a 'make more true' and

 * static_branch_dec() as a 'make more false'. The inc()/dec()

 * interface is meant to be used exclusively from the inc()/dec() for a given

 * key.

 * static_branch_dec() as a 'make more false'.

 *

 * Since this relies on modifying code, the branch modifying functions

 * must be considered absolute slow paths (machine wide synchronization etc.).

kernel/locking/qspinlock.c

+1 −1
Original line number Diff line number Diff line
@@ -289,7 +289,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) 
	if (pv_enabled())

		goto queue;



	if (virt_queued_spin_lock(lock))

	if (virt_spin_lock(lock))

		return;



	/*