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doc: Make checklist.rst note that spinlocks are implied RCU readers

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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 checklist.rst to document this non-obvious case.

While in the area, fix a typo by changing "read-side critical" to
"read-side critical section".

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
This commit is contained in:
Paul E. McKenney 2023-11-24 16:23:56 -08:00 committed by Boqun Feng
parent 8dbc33b4d1
commit 3cf5016121
1 changed files with 3 additions and 2 deletions
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5
Documentation/RCU/checklist.rst
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@ -68,7 +68,8 @@ over a rather long period of time, but improvements are always welcome!
rcu_read_lock_sched(), or by the appropriate update-side lock.
Explicit disabling of preemption (preempt_disable(), for example)
can serve as rcu_read_lock_sched(), but is less readable and
prevents lockdep from detecting locking issues.
prevents lockdep from detecting locking issues. Acquiring a
spinlock also enters an RCU read-side critical section.
Please note that you *cannot* rely on code known to be built
only in non-preemptible kernels. Such code can and will break,
@ -444,7 +445,7 @@ over a rather long period of time, but improvements are always welcome!
real-time workloads than is synchronize_rcu_expedited().
It is also permissible to sleep in RCU Tasks Trace read-side
critical, which are delimited by rcu_read_lock_trace() and
critical section, which are delimited by rcu_read_lock_trace() and
rcu_read_unlock_trace(). However, this is a specialized flavor
of RCU, and you should not use it without first checking with
its current users. In most cases, you should instead use SRCU.