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: Waiman Long <longman@redhat.com>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 2ea18a3def045b4f71ccea1cf428a92d8d50734b..148983e21d4707bdf3d821a1059c1e0efe4be7f9 100644 (file)
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -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)                                \

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 0b1f779572402d4736783cbc890bfbf748416b38..c0500679fd2f568fa0548b75d75bb4e43b72aaea 100644 (file)
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -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
 }

diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
index 64877f5294e35b194232b1dca59e0db84d48d32c..eb9c8534299b93ab526a8f20965aaebb02802433 100644 (file)
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -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)
 {
 }

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cbdfae37989653410332bc9acd9dd1237ace1712..417bdd9e80fbd38f5e30e19cecbae9e1b37fdffb 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -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"