diff options
| author | Paul E. McKenney <paulmck@kernel.org> | 2023-11-24 15:06:46 -0800 |
|---|---|---|
| committer | Boqun Feng <boqun.feng@gmail.com> | 2024-02-14 07:53:49 -0800 |
| commit | 8dbc33b4d1a19ff43930dc983c457946241078e8 (patch) | |
| tree | 60b585da1e2ce8d58475921516c244019525c6ee /Documentation/RCU/whatisRCU.rst | |
| parent | 120311acb01d7360dcc70c0862c83758fbcd28d2 (diff) | |
doc: Make whatisRCU.rst note that spinlocks are RCU readers
In kernels built with CONFIG_PREEMPT_RT=n, spinlock critical sections
are RCU readers because they disable preemption. However, they are also
RCU readers in CONFIG_PREEMPT_RT=y because in that case the locking
primitives contain rcu_read_lock() and rcu_read_unlock(). Therefore,
upgrade whatisRCU.rst to document this non-obvious case.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Diffstat (limited to 'Documentation/RCU/whatisRCU.rst')
| -rw-r--r-- | Documentation/RCU/whatisRCU.rst | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst index 60ce02475142..246ce0d0b4d1 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() ^^^^^^^^^^^^^^^^^ |