diff options
Diffstat (limited to 'Documentation/locking')
| -rw-r--r-- | Documentation/locking/hwspinlock.rst | 57 | ||||
| -rw-r--r-- | Documentation/locking/index.rst | 7 | ||||
| -rw-r--r-- | Documentation/locking/locktypes.rst | 21 | ||||
| -rw-r--r-- | Documentation/locking/seqlock.rst | 11 |
4 files changed, 29 insertions, 67 deletions
diff --git a/Documentation/locking/hwspinlock.rst b/Documentation/locking/hwspinlock.rst index 2ffaa3cbd63f..a737c702a7d1 100644 --- a/Documentation/locking/hwspinlock.rst +++ b/Documentation/locking/hwspinlock.rst @@ -40,17 +40,6 @@ User API :: - struct hwspinlock *hwspin_lock_request(void); - -Dynamically assign an hwspinlock and return its address, or NULL -in case an unused hwspinlock isn't available. Users of this -API will usually want to communicate the lock's id to the remote core -before it can be used to achieve synchronization. - -Should be called from a process context (might sleep). - -:: - struct hwspinlock *hwspin_lock_request_specific(unsigned int id); Assign a specific hwspinlock id and return its address, or NULL @@ -312,17 +301,6 @@ The caller should **never** unlock an hwspinlock which is already unlocked. Doing so is considered a bug (there is no protection against this). This function will never sleep. -:: - - int hwspin_lock_get_id(struct hwspinlock *hwlock); - -Retrieve id number of a given hwspinlock. This is needed when an -hwspinlock is dynamically assigned: before it can be used to achieve -mutual exclusion with a remote cpu, the id number should be communicated -to the remote task with which we want to synchronize. - -Returns the hwspinlock id number, or -EINVAL if hwlock is null. - Typical usage ============= @@ -331,40 +309,7 @@ Typical usage #include <linux/hwspinlock.h> #include <linux/err.h> - int hwspinlock_example1(void) - { - struct hwspinlock *hwlock; - int ret; - - /* dynamically assign a hwspinlock */ - hwlock = hwspin_lock_request(); - if (!hwlock) - ... - - id = hwspin_lock_get_id(hwlock); - /* probably need to communicate id to a remote processor now */ - - /* take the lock, spin for 1 sec if it's already taken */ - ret = hwspin_lock_timeout(hwlock, 1000); - if (ret) - ... - - /* - * we took the lock, do our thing now, but do NOT sleep - */ - - /* release the lock */ - hwspin_unlock(hwlock); - - /* free the lock */ - ret = hwspin_lock_free(hwlock); - if (ret) - ... - - return ret; - } - - int hwspinlock_example2(void) + int hwspinlock_example(void) { struct hwspinlock *hwlock; int ret; diff --git a/Documentation/locking/index.rst b/Documentation/locking/index.rst index 6a9ea96c8bcb..9278d95b7dcb 100644 --- a/Documentation/locking/index.rst +++ b/Documentation/locking/index.rst @@ -24,10 +24,3 @@ Locking percpu-rw-semaphore robust-futexes robust-futex-ABI - -.. only:: subproject and html - - Indices - ======= - - * :ref:`genindex` diff --git a/Documentation/locking/locktypes.rst b/Documentation/locking/locktypes.rst index 80c914f6eae7..37b6a5670c2f 100644 --- a/Documentation/locking/locktypes.rst +++ b/Documentation/locking/locktypes.rst @@ -204,6 +204,27 @@ per-CPU data structures on a non PREEMPT_RT kernel. local_lock is not suitable to protect against preemption or interrupts on a PREEMPT_RT kernel due to the PREEMPT_RT specific spinlock_t semantics. +CPU local scope and bottom-half +------------------------------- + +Per-CPU variables that are accessed only in softirq context should not rely on +the assumption that this context is implicitly protected due to being +non-preemptible. In a PREEMPT_RT kernel, softirq context is preemptible, and +synchronizing every bottom-half-disabled section via implicit context results +in an implicit per-CPU "big kernel lock." + +A local_lock_t together with local_lock_nested_bh() and +local_unlock_nested_bh() for locking operations help to identify the locking +scope. + +When lockdep is enabled, these functions verify that data structure access +occurs within softirq context. +Unlike local_lock(), local_unlock_nested_bh() does not disable preemption and +does not add overhead when used without lockdep. + +On a PREEMPT_RT kernel, local_lock_t behaves as a real lock and +local_unlock_nested_bh() serializes access to the data structure, which allows +removal of serialization via local_bh_disable(). raw_spinlock_t and spinlock_t ============================= diff --git a/Documentation/locking/seqlock.rst b/Documentation/locking/seqlock.rst index ec6411d02ac8..9899871d3d9a 100644 --- a/Documentation/locking/seqlock.rst +++ b/Documentation/locking/seqlock.rst @@ -1,3 +1,5 @@ +.. SPDX-License-Identifier: GPL-2.0 + ====================================== Sequence counters and sequential locks ====================================== @@ -218,13 +220,14 @@ Read path, three categories: according to a passed marker. This is used to avoid lockless readers starvation (too much retry loops) in case of a sharp spike in write activity. First, a lockless read is tried (even marker passed). If - that trial fails (odd sequence counter is returned, which is used as - the next iteration marker), the lockless read is transformed to a - full locking read and no retry loop is necessary:: + that trial fails (sequence counter doesn't match), make the marker + odd for the next iteration, the lockless read is transformed to a + full locking read and no retry loop is necessary, for example:: /* marker; even initialization */ - int seq = 0; + int seq = 1; do { + seq++; /* 2 on the 1st/lockless path, otherwise odd */ read_seqbegin_or_lock(&foo_seqlock, &seq); /* ... [[read-side critical section]] ... */ |