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Diffstat (limited to 'Documentation/RCU/whatisRCU.rst')
| -rw-r--r-- | Documentation/RCU/whatisRCU.rst | 19 |
1 files changed, 15 insertions, 4 deletions
diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst index 60ce02475142d8..872ac665223fbd 100644 --- a/Documentation/RCU/whatisRCU.rst +++ b/Documentation/RCU/whatisRCU.rst @@ -172,14 +172,25 @@ rcu_read_lock() critical section. Reference counts may be used in conjunction with RCU to maintain longer-term references to data structures. + Note that anything that disables bottom halves, preemption, + or interrupts also enters an RCU read-side critical section. + Acquiring a spinlock also enters an RCU read-side critical + sections, even for spinlocks that do not disable preemption, + as is the case in kernels built with CONFIG_PREEMPT_RT=y. + Sleeplocks do *not* enter RCU read-side critical sections. + rcu_read_unlock() ^^^^^^^^^^^^^^^^^ void rcu_read_unlock(void); This temporal primitives is used by a reader to inform the reclaimer that the reader is exiting an RCU read-side critical - section. Note that RCU read-side critical sections may be nested - and/or overlapping. + section. Anything that enables bottom halves, preemption, + or interrupts also exits an RCU read-side critical section. + Releasing a spinlock also exits an RCU read-side critical section. + + Note that RCU read-side critical sections may be nested and/or + overlapping. synchronize_rcu() ^^^^^^^^^^^^^^^^^ @@ -952,8 +963,8 @@ unfortunately any spinlock in a ``SLAB_TYPESAFE_BY_RCU`` object must be initialized after each and every call to kmem_cache_alloc(), which renders reference-free spinlock acquisition completely unsafe. Therefore, when using ``SLAB_TYPESAFE_BY_RCU``, make proper use of a reference counter. -(Those willing to use a kmem_cache constructor may also use locking, -including cache-friendly sequence locking.) +(Those willing to initialize their locks in a kmem_cache constructor +may also use locking, including cache-friendly sequence locking.) With traditional reference counting -- such as that implemented by the kref library in Linux -- there is typically code that runs when the last |