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: Waiman Long <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index f549c552dbf1e376a412efc1cb7a95a7029f2f7a..30465a2f2b6cf8e072ee797d1b58219f0799cb66 100644 (file)
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -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);
 }
 

diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
index a883b8f1fdc6efbadcab3ca130120cd28130e518..a17cba8d94bb10b4e3d6d038ea90259349e8a193 100644 (file)
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -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);
 }
 

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 64155e310a9f2119ee7443268e767fc74b32043e..88650ab5cedb2936fe52f1c0b9ecba83ead89e78 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -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