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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-18 18:50:12 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-18 18:50:12 +0000
commit8665bd53f2f2e27e5511d90428cb3f60e6d0ce15 (patch)
tree8d58900dc0ebd4a3011f92c128d2fe45bc7c4bf2 /Documentation/RCU
parentAdding debian version 6.7.12-1. (diff)
downloadlinux-8665bd53f2f2e27e5511d90428cb3f60e6d0ce15.tar.xz
linux-8665bd53f2f2e27e5511d90428cb3f60e6d0ce15.zip
Merging upstream version 6.8.9.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/checklist.rst25
-rw-r--r--Documentation/RCU/rcu_dereference.rst27
-rw-r--r--Documentation/RCU/torture.rst2
3 files changed, 37 insertions, 17 deletions
diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst
index bd3c58c44b..2d42998a89 100644
--- a/Documentation/RCU/checklist.rst
+++ b/Documentation/RCU/checklist.rst
@@ -241,15 +241,22 @@ over a rather long period of time, but improvements are always welcome!
srcu_struct. The rules for the expedited RCU grace-period-wait
primitives are the same as for their non-expedited counterparts.
- If the updater uses call_rcu_tasks() or synchronize_rcu_tasks(),
- then the readers must refrain from executing voluntary
- context switches, that is, from blocking. If the updater uses
- call_rcu_tasks_trace() or synchronize_rcu_tasks_trace(), then
- the corresponding readers must use rcu_read_lock_trace() and
- rcu_read_unlock_trace(). If an updater uses call_rcu_tasks_rude()
- or synchronize_rcu_tasks_rude(), then the corresponding readers
- must use anything that disables preemption, for example,
- preempt_disable() and preempt_enable().
+ Similarly, it is necessary to correctly use the RCU Tasks flavors:
+
+ a. If the updater uses synchronize_rcu_tasks() or
+ call_rcu_tasks(), then the readers must refrain from
+ executing voluntary context switches, that is, from
+ blocking.
+
+ b. If the updater uses call_rcu_tasks_trace()
+ or synchronize_rcu_tasks_trace(), then the
+ corresponding readers must use rcu_read_lock_trace()
+ and rcu_read_unlock_trace().
+
+ c. If an updater uses call_rcu_tasks_rude() or
+ synchronize_rcu_tasks_rude(), then the corresponding
+ readers must use anything that disables preemption,
+ for example, preempt_disable() and preempt_enable().
Mixing things up will result in confusion and broken kernels, and
has even resulted in an exploitable security issue. Therefore,
diff --git a/Documentation/RCU/rcu_dereference.rst b/Documentation/RCU/rcu_dereference.rst
index 3b739f6243..659d591378 100644
--- a/Documentation/RCU/rcu_dereference.rst
+++ b/Documentation/RCU/rcu_dereference.rst
@@ -3,13 +3,26 @@
PROPER CARE AND FEEDING OF RETURN VALUES FROM rcu_dereference()
===============================================================
-Most of the time, you can use values from rcu_dereference() or one of
-the similar primitives without worries. Dereferencing (prefix "*"),
-field selection ("->"), assignment ("="), address-of ("&"), addition and
-subtraction of constants, and casts all work quite naturally and safely.
-
-It is nevertheless possible to get into trouble with other operations.
-Follow these rules to keep your RCU code working properly:
+Proper care and feeding of address and data dependencies is critically
+important to correct use of things like RCU. To this end, the pointers
+returned from the rcu_dereference() family of primitives carry address and
+data dependencies. These dependencies extend from the rcu_dereference()
+macro's load of the pointer to the later use of that pointer to compute
+either the address of a later memory access (representing an address
+dependency) or the value written by a later memory access (representing
+a data dependency).
+
+Most of the time, these dependencies are preserved, permitting you to
+freely use values from rcu_dereference(). For example, dereferencing
+(prefix "*"), field selection ("->"), assignment ("="), address-of
+("&"), casts, and addition or subtraction of constants all work quite
+naturally and safely. However, because current compilers do not take
+either address or data dependencies into account it is still possible
+to get into trouble.
+
+Follow these rules to preserve the address and data dependencies emanating
+from your calls to rcu_dereference() and friends, thus keeping your RCU
+readers working properly:
- You must use one of the rcu_dereference() family of primitives
to load an RCU-protected pointer, otherwise CONFIG_PROVE_RCU
diff --git a/Documentation/RCU/torture.rst b/Documentation/RCU/torture.rst
index b3b6dfa852..49e7beea6a 100644
--- a/Documentation/RCU/torture.rst
+++ b/Documentation/RCU/torture.rst
@@ -185,7 +185,7 @@ argument.
Not all changes require that all scenarios be run. For example, a change
to Tree SRCU might run only the SRCU-N and SRCU-P scenarios using the
--configs argument to kvm.sh as follows: "--configs 'SRCU-N SRCU-P'".
-Large systems can run multiple copies of of the full set of scenarios,
+Large systems can run multiple copies of the full set of scenarios,
for example, a system with 448 hardware threads can run five instances
of the full set concurrently. To make this happen::