v2:
- Add Boqun's "Reviewed-by" tags & twist the mutex patch as suggested
by him.
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 | 8 ++------
kernel/locking/qspinlock_paravirt.h | 2 +-
kernel/locking/rwsem.c | 6 +++---
lib/Kconfig.debug | 4 ++--
4 files changed, 8 insertions(+), 12 deletions(-)
--
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]>
Reviewed-by: Boqun Feng <[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 up the mutex_destroy() function
declaration and the __DEBUG_MUTEX_INITIALIZER() macro above the "#ifndef
CONFIG_PREEMPT_RT" section 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]>
---
include/linux/mutex.h | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 7e208d46ba5b..67edc4ca2bee 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -32,11 +32,9 @@
# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
#endif
-#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);
@@ -49,6 +47,7 @@ static inline void mutex_destroy(struct mutex *lock) {}
#endif
+#ifndef CONFIG_PREEMPT_RT
/**
* mutex_init - initialize the mutex
* @mutex: the mutex to be initialized
@@ -101,9 +100,6 @@ 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)
--
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]>
Reviewed-by: Boqun Feng <[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
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]>
---
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
The following commit has been merged into the locking/core branch of tip:
Commit-ID: f22f71322a18e90e127f2fc2c11cc2d5191bc4c6
Gitweb: https://git.kernel.org/tip/f22f71322a18e90e127f2fc2c11cc2d5191bc4c6
Author: Waiman Long <[email protected]>
AuthorDate: Thu, 22 Feb 2024 10:05:40 -05:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Wed, 28 Feb 2024 13:08:38 +01:00
locking/rwsem: Make DEBUG_RWSEMS and PREEMPT_RT mutually exclusive
The debugging code enabled by CONFIG_DEBUG_RWSEMS=y 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]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
lib/Kconfig.debug | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 975a07f..cb695bc 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.
The following commit has been merged into the locking/core branch of tip:
Commit-ID: d6cac0b6b0115fd0a5f51a49401473626e4e4fe7
Gitweb: https://git.kernel.org/tip/d6cac0b6b0115fd0a5f51a49401473626e4e4fe7
Author: Waiman Long <[email protected]>
AuthorDate: Thu, 22 Feb 2024 10:05:38 -05:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Wed, 28 Feb 2024 13:08:37 +01:00
locking/mutex: Simplify <linux/mutex.h>
CONFIG_DEBUG_MUTEXES and CONFIG_PREEMPT_RT are mutually exclusive. They
can't be both set at the same time. Move up the mutex_destroy() function
declaration and the __DEBUG_MUTEX_INITIALIZER() macro above the "#ifndef
CONFIG_PREEMPT_RT" section 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]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
include/linux/mutex.h | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 7e208d4..67edc4c 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -32,11 +32,9 @@
# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
#endif
-#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);
@@ -49,6 +47,7 @@ static inline void mutex_destroy(struct mutex *lock) {}
#endif
+#ifndef CONFIG_PREEMPT_RT
/**
* mutex_init - initialize the mutex
* @mutex: the mutex to be initialized
@@ -101,9 +100,6 @@ 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)
The following commit has been merged into the locking/core branch of tip:
Commit-ID: ca4bc2e07b716509fd279d2b449bb42f4263a9c8
Gitweb: https://git.kernel.org/tip/ca4bc2e07b716509fd279d2b449bb42f4263a9c8
Author: Waiman Long <[email protected]>
AuthorDate: Thu, 22 Feb 2024 10:05:37 -05:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Wed, 28 Feb 2024 13:08:37 +01:00
locking/qspinlock: Fix 'wait_early' set but not used warning
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]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Closes: https://lore.kernel.org/oe-kbuild-all/[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 6a0184e..ae2b12f 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--) {
The following commit has been merged into the locking/core branch of tip:
Commit-ID: d566c78659eccf085f905fd266fc461de92eaa8f
Gitweb: https://git.kernel.org/tip/d566c78659eccf085f905fd266fc461de92eaa8f
Author: Waiman Long <[email protected]>
AuthorDate: Thu, 22 Feb 2024 10:05:39 -05:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Wed, 28 Feb 2024 13:08:38 +01:00
locking/rwsem: Clarify that RWSEM_READER_OWNED is just a hint
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]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Link: https://lore.kernel.org/r/[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 2340b6d..c6d17ae 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))
* tip-bot2 for Waiman Long <[email protected]> wrote:
> The following commit has been merged into the locking/core branch of tip:
>
> Commit-ID: ca4bc2e07b716509fd279d2b449bb42f4263a9c8
> Gitweb: https://git.kernel.org/tip/ca4bc2e07b716509fd279d2b449bb42f4263a9c8
> Author: Waiman Long <[email protected]>
> AuthorDate: Thu, 22 Feb 2024 10:05:37 -05:00
> Committer: Ingo Molnar <[email protected]>
> CommitterDate: Wed, 28 Feb 2024 13:08:37 +01:00
>
> locking/qspinlock: Fix 'wait_early' set but not used warning
>
> 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]>
> Signed-off-by: Waiman Long <[email protected]>
> Signed-off-by: Ingo Molnar <[email protected]>
> Reviewed-by: Boqun Feng <[email protected]>
> Cc: Linus Torvalds <[email protected]>
> Link: https://lore.kernel.org/r/[email protected]
>
> Closes: https://lore.kernel.org/oe-kbuild-all/[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 6a0184e..ae2b12f 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;
On a second thought, shouldn't this be solved via lockevent_cond_inc()'s
!CONFIG_LOCK_EVENT_COUNTS stub explicitly marking the variable as used, via
!something like:
#define lockevent_cond_inc(ev, c) do { (void)(c); } while (0)
or so, instead of uglifying the usage site?
Thanks,
Ingo
On 3/11/24 06:57, Ingo Molnar wrote:
> * tip-bot2 for Waiman Long <[email protected]> wrote:
>
>> The following commit has been merged into the locking/core branch of tip:
>>
>> Commit-ID: ca4bc2e07b716509fd279d2b449bb42f4263a9c8
>> Gitweb: https://git.kernel.org/tip/ca4bc2e07b716509fd279d2b449bb42f4263a9c8
>> Author: Waiman Long <[email protected]>
>> AuthorDate: Thu, 22 Feb 2024 10:05:37 -05:00
>> Committer: Ingo Molnar <[email protected]>
>> CommitterDate: Wed, 28 Feb 2024 13:08:37 +01:00
>>
>> locking/qspinlock: Fix 'wait_early' set but not used warning
>>
>> 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]>
>> Signed-off-by: Waiman Long <[email protected]>
>> Signed-off-by: Ingo Molnar <[email protected]>
>> Reviewed-by: Boqun Feng <[email protected]>
>> Cc: Linus Torvalds <[email protected]>
>> Link: https://lore.kernel.org/r/[email protected]
>>
>> Closes: https://lore.kernel.org/oe-kbuild-all/[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 6a0184e..ae2b12f 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;
> On a second thought, shouldn't this be solved via lockevent_cond_inc()'s
> !CONFIG_LOCK_EVENT_COUNTS stub explicitly marking the variable as used, via
> !something like:
>
> #define lockevent_cond_inc(ev, c) do { (void)(c); } while (0)
>
> or so, instead of uglifying the usage site?
Right, that should work too. Thanks for the suggestion. I will post
another to do that.
Cheers,
Longman