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-rw-r--r--Documentation/RCU/checklist.rst32
-rw-r--r--Documentation/RCU/rcu_dereference.rst5
-rw-r--r--Documentation/RCU/torture.rst2
-rw-r--r--Documentation/RCU/whatisRCU.rst19
4 files changed, 40 insertions, 18 deletions
diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst
index 2d42998a89..3e6407de23 100644
--- a/Documentation/RCU/checklist.rst
+++ b/Documentation/RCU/checklist.rst
@@ -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,
@@ -382,16 +383,17 @@ over a rather long period of time, but improvements are always welcome!
must use whatever locking or other synchronization is required
to safely access and/or modify that data structure.
- Do not assume that RCU callbacks will be executed on the same
- CPU that executed the corresponding call_rcu() or call_srcu().
- For example, if a given CPU goes offline while having an RCU
- callback pending, then that RCU callback will execute on some
- surviving CPU. (If this was not the case, a self-spawning RCU
- callback would prevent the victim CPU from ever going offline.)
- Furthermore, CPUs designated by rcu_nocbs= might well *always*
- have their RCU callbacks executed on some other CPUs, in fact,
- for some real-time workloads, this is the whole point of using
- the rcu_nocbs= kernel boot parameter.
+ Do not assume that RCU callbacks will be executed on
+ the same CPU that executed the corresponding call_rcu(),
+ call_srcu(), call_rcu_tasks(), call_rcu_tasks_rude(), or
+ call_rcu_tasks_trace(). For example, if a given CPU goes offline
+ while having an RCU callback pending, then that RCU callback
+ will execute on some surviving CPU. (If this was not the case,
+ a self-spawning RCU callback would prevent the victim CPU from
+ ever going offline.) Furthermore, CPUs designated by rcu_nocbs=
+ might well *always* have their RCU callbacks executed on some
+ other CPUs, in fact, for some real-time workloads, this is the
+ whole point of using the rcu_nocbs= kernel boot parameter.
In addition, do not assume that callbacks queued in a given order
will be invoked in that order, even if they all are queued on the
@@ -444,7 +446,7 @@ 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.
@@ -490,6 +492,12 @@ over a rather long period of time, but improvements are always welcome!
since the last time that you passed that same object to
call_rcu() (or friends).
+ CONFIG_RCU_STRICT_GRACE_PERIOD:
+ combine with KASAN to check for pointers leaked out
+ of RCU read-side critical sections. This Kconfig
+ option is tough on both performance and scalability,
+ and so is limited to four-CPU systems.
+
__rcu sparse checks:
tag the pointer to the RCU-protected data structure
with __rcu, and sparse will warn you if you access that
diff --git a/Documentation/RCU/rcu_dereference.rst b/Documentation/RCU/rcu_dereference.rst
index 659d591378..2524dcdadd 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,
diff --git a/Documentation/RCU/torture.rst b/Documentation/RCU/torture.rst
index 49e7beea6a..4b1f99c418 100644
--- a/Documentation/RCU/torture.rst
+++ b/Documentation/RCU/torture.rst
@@ -318,7 +318,7 @@ Suppose that a previous kvm.sh run left its output in this directory::
tools/testing/selftests/rcutorture/res/2022.11.03-11.26.28
-Then this run can be re-run without rebuilding as follow:
+Then this run can be re-run without rebuilding as follow::
kvm-again.sh tools/testing/selftests/rcutorture/res/2022.11.03-11.26.28
diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst
index 60ce024751..872ac66522 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