From: Paul E. McKenney Date: Fri, 24 Nov 2023 23:06:46 +0000 (-0800) Subject: doc: Make whatisRCU.rst note that spinlocks are RCU readers X-Git-Tag: v6.9-rc1~213^2~7 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8dbc33b4d1a19ff43930dc983c457946241078e8;p=thirdparty%2Fkernel%2Flinux.git 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 Signed-off-by: Boqun Feng --- diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst index 60ce02475142d..246ce0d0b4d11 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() ^^^^^^^^^^^^^^^^^