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Commit 5149cbac authored by Waiman Long's avatar Waiman Long Committed by Ingo Molnar
Browse files

locking/rwsem: Add DEBUG_RWSEMS to look for lock/unlock mismatches 



For a rwsem, locking can either be exclusive or shared. The corresponding
exclusive or shared unlock must be used. Otherwise, the protected data
structures may get corrupted or the lock may be in an inconsistent state.

In order to detect such anomaly, a new configuration option DEBUG_RWSEMS
is added which can be enabled to look for such mismatches and print
warnings that that happens.

Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Acked-by: default avatarDavidlohr Bueso <dave@stgolabs.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1522445280-7767-2-git-send-email-longman@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 169310f7

kernel/locking/rwsem.c

+4 −0
Original line number Diff line number Diff line
@@ -117,6 +117,7 @@ EXPORT_SYMBOL(down_write_trylock); 
void up_read(struct rw_semaphore *sem)

{

	rwsem_release(&sem->dep_map, 1, _RET_IP_);

	DEBUG_RWSEMS_WARN_ON(sem->owner != RWSEM_READER_OWNED);



	__up_read(sem);

}
@@ -129,6 +130,7 @@ EXPORT_SYMBOL(up_read); 
void up_write(struct rw_semaphore *sem)

{

	rwsem_release(&sem->dep_map, 1, _RET_IP_);

	DEBUG_RWSEMS_WARN_ON(sem->owner != current);



	rwsem_clear_owner(sem);

	__up_write(sem);
@@ -142,6 +144,7 @@ EXPORT_SYMBOL(up_write); 
void downgrade_write(struct rw_semaphore *sem)

{

	lock_downgrade(&sem->dep_map, _RET_IP_);

	DEBUG_RWSEMS_WARN_ON(sem->owner != current);



	rwsem_set_reader_owned(sem);

	__downgrade_write(sem);
@@ -211,6 +214,7 @@ EXPORT_SYMBOL(down_write_killable_nested); 


void up_read_non_owner(struct rw_semaphore *sem)

{

	DEBUG_RWSEMS_WARN_ON(sem->owner != RWSEM_READER_OWNED);

	__up_read(sem);

}

kernel/locking/rwsem.h

+7 −1
Original line number Diff line number Diff line
@@ -16,6 +16,12 @@ 
 */

#define RWSEM_READER_OWNED	((struct task_struct *)1UL)



#ifdef CONFIG_DEBUG_RWSEMS

# define DEBUG_RWSEMS_WARN_ON(c)	DEBUG_LOCKS_WARN_ON(c)

#else

# define DEBUG_RWSEMS_WARN_ON(c)

#endif



#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

/*

 * All writes to owner are protected by WRITE_ONCE() to make sure that
@@ -41,7 +47,7 @@ static inline void rwsem_set_reader_owned(struct rw_semaphore *sem) 
	 * do a write to the rwsem cacheline when it is really necessary

	 * to minimize cacheline contention.

	 */

	if (sem->owner != RWSEM_READER_OWNED)

	if (READ_ONCE(sem->owner) != RWSEM_READER_OWNED)

		WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);

}

lib/Kconfig.debug

+8 −0
Original line number Diff line number Diff line
@@ -1075,6 +1075,13 @@ config DEBUG_WW_MUTEX_SLOWPATH 
	 even a debug kernel.  If you are a driver writer, enable it.  If

	 you are a distro, do not.



config DEBUG_RWSEMS

	bool "RW Semaphore debugging: basic checks"

	depends on DEBUG_KERNEL && RWSEM_SPIN_ON_OWNER

	help

	  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"

	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
@@ -1097,6 +1104,7 @@ 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_LOCK_ALLOC

	select TRACE_IRQFLAGS

	default n