This series contains a number of cleanup locking patches.
Waiman Long (4):
locking/qspinlock: Fix 'wait_early' set but not used warning
locking/mutex: Clean up mutex.h
locking/rwsem: Clarify that RWSEM_READER_OWNED is just a hint
locking/rwsem: Make DEBUG_RWSEMS and PREEMPT_RT mutually exclusive
include/linux/mutex.h | 23 +++++++++++------------
kernel/locking/qspinlock_paravirt.h | 2 +-
kernel/locking/rwsem.c | 6 +++---
lib/Kconfig.debug | 4 ++--
4 files changed, 17 insertions(+), 18 deletions(-)
--
2.39.3
The debugging code enabled by CONFIG_DEBUG_RWSEMS will only be
compiled in when CONFIG_PREEMPT_RT isn't set. There is no point to
allow CONFIG_DEBUG_RWSEMS to be set in a kernel configuration where
CONFIG_PREEMPT_RT is also set. Make them mutually exclusive.
Signed-off-by: Waiman Long <[email protected]>
---
lib/Kconfig.debug | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 975a07f9f1cc..cb695bc76d30 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1303,7 +1303,7 @@ config PROVE_LOCKING
select DEBUG_SPINLOCK
select DEBUG_MUTEXES if !PREEMPT_RT
select DEBUG_RT_MUTEXES if RT_MUTEXES
- select DEBUG_RWSEMS
+ select DEBUG_RWSEMS if !PREEMPT_RT
select DEBUG_WW_MUTEX_SLOWPATH
select DEBUG_LOCK_ALLOC
select PREEMPT_COUNT if !ARCH_NO_PREEMPT
@@ -1426,7 +1426,7 @@ config DEBUG_WW_MUTEX_SLOWPATH
config DEBUG_RWSEMS
bool "RW Semaphore debugging: basic checks"
- depends on DEBUG_KERNEL
+ depends on DEBUG_KERNEL && !PREEMPT_RT
help
This debugging feature allows mismatched rw semaphore locks
and unlocks to be detected and reported.
--
2.39.3
When CONFIG_LOCK_EVENT_COUNTS is off, the wait_early variable will be
set but not used. This is expected. Recent compilers will not generate
wait_early code in this case.
Add the __maybe_unused attribute to wait_early for suppressing this
W=1 warning.
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Waiman Long <[email protected]>
---
kernel/locking/qspinlock_paravirt.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 6a0184e9c234..ae2b12f68b90 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -294,8 +294,8 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
{
struct pv_node *pn = (struct pv_node *)node;
struct pv_node *pp = (struct pv_node *)prev;
+ bool __maybe_unused wait_early;
int loop;
- bool wait_early;
for (;;) {
for (wait_early = false, loop = SPIN_THRESHOLD; loop; loop--) {
--
2.39.3
CONFIG_DEBUG_MUTEXES and CONFIG_PREEMPT_RT are mutually exclusive. They
can't be both set at the same time. Move down the mutex_destroy()
function declaration to the bottom of mutex.h to eliminate duplicated
mutex_destroy() declaration.
Also remove the duplicated mutex_trylock() function declaration in the
CONFIG_PREEMPT_RT section.
Signed-off-by: Waiman Long <[email protected]>
---
include/linux/mutex.h | 23 +++++++++++------------
1 file changed, 11 insertions(+), 12 deletions(-)
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 7e208d46ba5b..bad383713db2 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -35,18 +35,10 @@
#ifndef CONFIG_PREEMPT_RT
#ifdef CONFIG_DEBUG_MUTEXES
-
-#define __DEBUG_MUTEX_INITIALIZER(lockname) \
+# define __DEBUG_MUTEX_INITIALIZER(lockname) \
, .magic = &lockname
-
-extern void mutex_destroy(struct mutex *lock);
-
#else
-
# define __DEBUG_MUTEX_INITIALIZER(lockname)
-
-static inline void mutex_destroy(struct mutex *lock) {}
-
#endif
/**
@@ -101,9 +93,6 @@ extern bool mutex_is_locked(struct mutex *lock);
extern void __mutex_rt_init(struct mutex *lock, const char *name,
struct lock_class_key *key);
-extern int mutex_trylock(struct mutex *lock);
-
-static inline void mutex_destroy(struct mutex *lock) { }
#define mutex_is_locked(l) rt_mutex_base_is_locked(&(l)->rtmutex)
@@ -170,6 +159,16 @@ extern void mutex_unlock(struct mutex *lock);
extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
+#ifdef CONFIG_DEBUG_MUTEXES
+
+extern void mutex_destroy(struct mutex *lock);
+
+#else
+
+static inline void mutex_destroy(struct mutex *lock) {}
+
+#endif
+
DEFINE_GUARD(mutex, struct mutex *, mutex_lock(_T), mutex_unlock(_T))
DEFINE_GUARD_COND(mutex, _try, mutex_trylock(_T))
DEFINE_GUARD_COND(mutex, _intr, mutex_lock_interruptible(_T) == 0)
--
2.39.3
Clarify in the comments that the RWSEM_READER_OWNED bit in the owner
field is just a hint, not an authoritative state of the rwsem.
Signed-off-by: Waiman Long <[email protected]>
---
kernel/locking/rwsem.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 2340b6d90ec6..c6d17aee4209 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -35,7 +35,7 @@
/*
* The least significant 2 bits of the owner value has the following
* meanings when set.
- * - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
+ * - Bit 0: RWSEM_READER_OWNED - rwsem may be owned by readers (just a hint)
* - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
*
* When the rwsem is reader-owned and a spinning writer has timed out,
@@ -1002,8 +1002,8 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
/*
* To prevent a constant stream of readers from starving a sleeping
- * waiter, don't attempt optimistic lock stealing if the lock is
- * currently owned by readers.
+ * writer, don't attempt optimistic lock stealing if the lock is
+ * very likely owned by readers.
*/
if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
(rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
--
2.39.3
On Mon, Feb 12, 2024 at 10:16:53PM -0500, Waiman Long wrote:
> When CONFIG_LOCK_EVENT_COUNTS is off, the wait_early variable will be
> set but not used. This is expected. Recent compilers will not generate
> wait_early code in this case.
>
> Add the __maybe_unused attribute to wait_early for suppressing this
> W=1 warning.
>
> Reported-by: kernel test robot <[email protected]>
> Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
> Signed-off-by: Waiman Long <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Regards,
Boqun
> ---
> kernel/locking/qspinlock_paravirt.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
> index 6a0184e9c234..ae2b12f68b90 100644
> --- a/kernel/locking/qspinlock_paravirt.h
> +++ b/kernel/locking/qspinlock_paravirt.h
> @@ -294,8 +294,8 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
> {
> struct pv_node *pn = (struct pv_node *)node;
> struct pv_node *pp = (struct pv_node *)prev;
> + bool __maybe_unused wait_early;
> int loop;
> - bool wait_early;
>
> for (;;) {
> for (wait_early = false, loop = SPIN_THRESHOLD; loop; loop--) {
> --
> 2.39.3
>
On Mon, Feb 12, 2024 at 10:16:55PM -0500, Waiman Long wrote:
> Clarify in the comments that the RWSEM_READER_OWNED bit in the owner
> field is just a hint, not an authoritative state of the rwsem.
>
> Signed-off-by: Waiman Long <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Regards,
Boqun
> ---
> kernel/locking/rwsem.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index 2340b6d90ec6..c6d17aee4209 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -35,7 +35,7 @@
> /*
> * The least significant 2 bits of the owner value has the following
> * meanings when set.
> - * - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
> + * - Bit 0: RWSEM_READER_OWNED - rwsem may be owned by readers (just a hint)
> * - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
> *
> * When the rwsem is reader-owned and a spinning writer has timed out,
> @@ -1002,8 +1002,8 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
>
> /*
> * To prevent a constant stream of readers from starving a sleeping
> - * waiter, don't attempt optimistic lock stealing if the lock is
> - * currently owned by readers.
> + * writer, don't attempt optimistic lock stealing if the lock is
> + * very likely owned by readers.
> */
> if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
> (rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
> --
> 2.39.3
>
On Mon, Feb 12, 2024 at 10:16:54PM -0500, Waiman Long wrote:
> CONFIG_DEBUG_MUTEXES and CONFIG_PREEMPT_RT are mutually exclusive. They
> can't be both set at the same time. Move down the mutex_destroy()
> function declaration to the bottom of mutex.h to eliminate duplicated
> mutex_destroy() declaration.
>
> Also remove the duplicated mutex_trylock() function declaration in the
> CONFIG_PREEMPT_RT section.
>
> Signed-off-by: Waiman Long <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Although, can you move the first "#ifdef CONFIG_DEBUG_MUTEXES" out of
the "#ifndef CONFIG_PREEMPT_RT" and combine it with the second one, i.e.
#ifdef CONFIG_DEBUG_MUTEXES
# define __DEBUG_MUTEX_INITIALIZER(lockname) ...
extern void mutex_destroy(struct mutex *lock);
#else
# define __DEBUG_MUTEX_INITIALIZER(lockname) ..
static inline void mutex_destroy(struct mutex *lock) {}
#endif
#ifndef CONFIG_PREEMPT_RT
...
Thoughts?
Regards,
Boqun
> ---
> include/linux/mutex.h | 23 +++++++++++------------
> 1 file changed, 11 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index 7e208d46ba5b..bad383713db2 100644
> --- a/include/linux/mutex.h
> +++ b/include/linux/mutex.h
> @@ -35,18 +35,10 @@
> #ifndef CONFIG_PREEMPT_RT
>
> #ifdef CONFIG_DEBUG_MUTEXES
> -
> -#define __DEBUG_MUTEX_INITIALIZER(lockname) \
> +# define __DEBUG_MUTEX_INITIALIZER(lockname) \
> , .magic = &lockname
> -
> -extern void mutex_destroy(struct mutex *lock);
> -
> #else
> -
> # define __DEBUG_MUTEX_INITIALIZER(lockname)
> -
> -static inline void mutex_destroy(struct mutex *lock) {}
> -
> #endif
>
> /**
> @@ -101,9 +93,6 @@ extern bool mutex_is_locked(struct mutex *lock);
>
> extern void __mutex_rt_init(struct mutex *lock, const char *name,
> struct lock_class_key *key);
> -extern int mutex_trylock(struct mutex *lock);
> -
> -static inline void mutex_destroy(struct mutex *lock) { }
>
> #define mutex_is_locked(l) rt_mutex_base_is_locked(&(l)->rtmutex)
>
> @@ -170,6 +159,16 @@ extern void mutex_unlock(struct mutex *lock);
>
> extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
>
> +#ifdef CONFIG_DEBUG_MUTEXES
> +
> +extern void mutex_destroy(struct mutex *lock);
> +
> +#else
> +
> +static inline void mutex_destroy(struct mutex *lock) {}
> +
> +#endif
> +
> DEFINE_GUARD(mutex, struct mutex *, mutex_lock(_T), mutex_unlock(_T))
> DEFINE_GUARD_COND(mutex, _try, mutex_trylock(_T))
> DEFINE_GUARD_COND(mutex, _intr, mutex_lock_interruptible(_T) == 0)
> --
> 2.39.3
>
On Mon, Feb 12, 2024 at 10:16:56PM -0500, Waiman Long wrote:
> The debugging code enabled by CONFIG_DEBUG_RWSEMS will only be
> compiled in when CONFIG_PREEMPT_RT isn't set. There is no point to
> allow CONFIG_DEBUG_RWSEMS to be set in a kernel configuration where
> CONFIG_PREEMPT_RT is also set. Make them mutually exclusive.
>
> Signed-off-by: Waiman Long <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Regards,
Boqun
> ---
> lib/Kconfig.debug | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 975a07f9f1cc..cb695bc76d30 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1303,7 +1303,7 @@ config PROVE_LOCKING
> select DEBUG_SPINLOCK
> select DEBUG_MUTEXES if !PREEMPT_RT
> select DEBUG_RT_MUTEXES if RT_MUTEXES
> - select DEBUG_RWSEMS
> + select DEBUG_RWSEMS if !PREEMPT_RT
> select DEBUG_WW_MUTEX_SLOWPATH
> select DEBUG_LOCK_ALLOC
> select PREEMPT_COUNT if !ARCH_NO_PREEMPT
> @@ -1426,7 +1426,7 @@ config DEBUG_WW_MUTEX_SLOWPATH
>
> config DEBUG_RWSEMS
> bool "RW Semaphore debugging: basic checks"
> - depends on DEBUG_KERNEL
> + depends on DEBUG_KERNEL && !PREEMPT_RT
> help
> This debugging feature allows mismatched rw semaphore locks
> and unlocks to be detected and reported.
> --
> 2.39.3
>
On 2/21/24 23:33, Boqun Feng wrote:
> On Mon, Feb 12, 2024 at 10:16:54PM -0500, Waiman Long wrote:
>> CONFIG_DEBUG_MUTEXES and CONFIG_PREEMPT_RT are mutually exclusive. They
>> can't be both set at the same time. Move down the mutex_destroy()
>> function declaration to the bottom of mutex.h to eliminate duplicated
>> mutex_destroy() declaration.
>>
>> Also remove the duplicated mutex_trylock() function declaration in the
>> CONFIG_PREEMPT_RT section.
>>
>> Signed-off-by: Waiman Long <[email protected]>
> Reviewed-by: Boqun Feng <[email protected]>
>
> Although, can you move the first "#ifdef CONFIG_DEBUG_MUTEXES" out of
> the "#ifndef CONFIG_PREEMPT_RT" and combine it with the second one, i.e.
>
> #ifdef CONFIG_DEBUG_MUTEXES
> # define __DEBUG_MUTEX_INITIALIZER(lockname) ...
> extern void mutex_destroy(struct mutex *lock);
> #else
> # define __DEBUG_MUTEX_INITIALIZER(lockname) ..
> static inline void mutex_destroy(struct mutex *lock) {}
> #endif
>
> #ifndef CONFIG_PREEMPT_RT
> ...
>
> Thoughts?
Sure. I can move it up and combine the two pieces.
Thanks for the review.
Cheers,
Longman
>
> Regards,
> Boqun
>
>> ---
>> include/linux/mutex.h | 23 +++++++++++------------
>> 1 file changed, 11 insertions(+), 12 deletions(-)
>>
>> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
>> index 7e208d46ba5b..bad383713db2 100644
>> --- a/include/linux/mutex.h
>> +++ b/include/linux/mutex.h
>> @@ -35,18 +35,10 @@
>> #ifndef CONFIG_PREEMPT_RT
>>
>> #ifdef CONFIG_DEBUG_MUTEXES
>> -
>> -#define __DEBUG_MUTEX_INITIALIZER(lockname) \
>> +# define __DEBUG_MUTEX_INITIALIZER(lockname) \
>> , .magic = &lockname
>> -
>> -extern void mutex_destroy(struct mutex *lock);
>> -
>> #else
>> -
>> # define __DEBUG_MUTEX_INITIALIZER(lockname)
>> -
>> -static inline void mutex_destroy(struct mutex *lock) {}
>> -
>> #endif
>>
>> /**
>> @@ -101,9 +93,6 @@ extern bool mutex_is_locked(struct mutex *lock);
>>
>> extern void __mutex_rt_init(struct mutex *lock, const char *name,
>> struct lock_class_key *key);
>> -extern int mutex_trylock(struct mutex *lock);
>> -
>> -static inline void mutex_destroy(struct mutex *lock) { }
>>
>> #define mutex_is_locked(l) rt_mutex_base_is_locked(&(l)->rtmutex)
>>
>> @@ -170,6 +159,16 @@ extern void mutex_unlock(struct mutex *lock);
>>
>> extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
>>
>> +#ifdef CONFIG_DEBUG_MUTEXES
>> +
>> +extern void mutex_destroy(struct mutex *lock);
>> +
>> +#else
>> +
>> +static inline void mutex_destroy(struct mutex *lock) {}
>> +
>> +#endif
>> +
>> DEFINE_GUARD(mutex, struct mutex *, mutex_lock(_T), mutex_unlock(_T))
>> DEFINE_GUARD_COND(mutex, _try, mutex_trylock(_T))
>> DEFINE_GUARD_COND(mutex, _intr, mutex_lock_interruptible(_T) == 0)
>> --
>> 2.39.3
>>