Commit c71fd893 authored by Waiman Long's avatar Waiman Long Committed by Ingo Molnar
Browse files

locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER 



The owner field in the rw_semaphore structure is used primarily for
optimistic spinning. However, identifying the rwsem owner can also be
helpful in debugging as well as tracing locking related issues when
analyzing crash dump. The owner field may also store state information
that can be important to the operation of the rwsem.

So the owner field is now made a permanent member of the rw_semaphore
structure irrespective of CONFIG_RWSEM_SPIN_ON_OWNER.

Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190520205918.22251-2-longman@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 69d927bb

include/linux/rwsem.h

+5 −4
Original line number Diff line number Diff line
@@ -34,12 +34,12 @@ 
 */

struct rw_semaphore {

	atomic_long_t count;

#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

	/*

	 * Write owner. Used as a speculative check to see

	 * if the owner is running on the cpu.

	 * Write owner or one of the read owners. Can be used as a

	 * speculative check to see if the owner is running on the cpu.

	 */

	struct task_struct *owner;

#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

	struct optimistic_spin_queue osq; /* spinner MCS lock */

#endif

	raw_spinlock_t wait_lock;
@@ -73,13 +73,14 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem) 
#endif



#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL

#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED

#else

#define __RWSEM_OPT_INIT(lockname)

#endif



#define __RWSEM_INITIALIZER(name)				\

	{ __RWSEM_INIT_COUNT(name),				\

	  .owner = NULL,					\

	  .wait_list = LIST_HEAD_INIT((name).wait_list),	\

	  .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock)	\

	  __RWSEM_OPT_INIT(name)				\

kernel/locking/rwsem-xadd.c

+1 −1
Original line number Diff line number Diff line
@@ -86,8 +86,8 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name, 
	atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);

	raw_spin_lock_init(&sem->wait_lock);

	INIT_LIST_HEAD(&sem->wait_list);

#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

	sem->owner = NULL;

#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

	osq_lock_init(&sem->osq);

#endif

}

kernel/locking/rwsem.h

+0 −23
Original line number Diff line number Diff line
@@ -61,7 +61,6 @@ 
#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS

#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)



#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

/*

 * All writes to owner are protected by WRITE_ONCE() to make sure that

 * store tearing can't happen as optimistic spinners may read and use
@@ -126,7 +125,6 @@ static inline bool rwsem_has_anonymous_owner(struct task_struct *owner) 
 * real owner or one of the real owners. The only exception is when the

 * unlock is done by up_read_non_owner().

 */

#define rwsem_clear_reader_owned rwsem_clear_reader_owned

static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)

{

	unsigned long val = (unsigned long)current | RWSEM_READER_OWNED
@@ -135,28 +133,7 @@ static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem) 
		cmpxchg_relaxed((unsigned long *)&sem->owner, val,

				RWSEM_READER_OWNED | RWSEM_ANONYMOUSLY_OWNED);

}

#endif



#else

static inline void rwsem_set_owner(struct rw_semaphore *sem)

{

}



static inline void rwsem_clear_owner(struct rw_semaphore *sem)

{

}



static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,

					   struct task_struct *owner)

{

}



static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)

{

}

#endif



#ifndef rwsem_clear_reader_owned

static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)

{

}

lib/Kconfig.debug

+4 −4
Original line number Diff line number Diff line
@@ -1095,7 +1095,7 @@ config PROVE_LOCKING 
	select DEBUG_SPINLOCK

	select DEBUG_MUTEXES

	select DEBUG_RT_MUTEXES if RT_MUTEXES

	select DEBUG_RWSEMS if RWSEM_SPIN_ON_OWNER

	select DEBUG_RWSEMS

	select DEBUG_WW_MUTEX_SLOWPATH

	select DEBUG_LOCK_ALLOC

	select TRACE_IRQFLAGS
@@ -1199,10 +1199,10 @@ config DEBUG_WW_MUTEX_SLOWPATH 


config DEBUG_RWSEMS

	bool "RW Semaphore debugging: basic checks"

	depends on DEBUG_KERNEL && RWSEM_SPIN_ON_OWNER

	depends on DEBUG_KERNEL

	help

	  This debugging feature allows mismatched rw semaphore locks and unlocks

	  to be detected and reported.

	  This debugging feature allows mismatched rw semaphore locks

	  and unlocks to be detected and reported.



config DEBUG_LOCK_ALLOC

	bool "Lock debugging: detect incorrect freeing of live locks"

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