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authorPaul E. McKenney <paulmck@kernel.org>2023-11-24 23:55:37 +0100
committerBoqun Feng <boqun.feng@gmail.com>2024-02-14 16:53:49 +0100
commit120311acb01d7360dcc70c0862c83758fbcd28d2 (patch)
tree57c50d1c5e3b886e2daadbd3924bbd5628226880 /Documentation/RCU
parentLinux 6.8-rc2 (diff)
downloadlinux-120311acb01d7360dcc70c0862c83758fbcd28d2.tar.xz
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doc: Spinlocks are implied 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 the -rt locking primitives contain rcu_read_lock() and rcu_read_unlock(). Therefore, upgrade rcu_dereference.rst to document this non-obvious case. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Closes: https://lore.kernel.org/lkml/CAHk-=whGKvjHCtJ6W4pQ0_h_k9fiFQ8V2GpM=BqYnB2X=SJ+XQ@mail.gmail.com/ Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/rcu_dereference.rst5
1 files changed, 4 insertions, 1 deletions
diff --git a/Documentation/RCU/rcu_dereference.rst b/Documentation/RCU/rcu_dereference.rst
index 659d5913784d..2524dcdadde2 100644
--- a/Documentation/RCU/rcu_dereference.rst
+++ b/Documentation/RCU/rcu_dereference.rst
@@ -408,7 +408,10 @@ member of the rcu_dereference() to use in various situations:
RCU flavors, an RCU read-side critical section is entered
using rcu_read_lock(), anything that disables bottom halves,
anything that disables interrupts, or anything that disables
- preemption.
+ preemption. Please note that spinlock critical sections
+ are also implied RCU read-side critical sections, even when
+ they are preemptible, as they are in kernels built with
+ CONFIG_PREEMPT_RT=y.
2. If the access might be within an RCU read-side critical section
on the one hand, or protected by (say) my_lock on the other,