diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/checklist.rst | 25 | ||||
| -rw-r--r-- | Documentation/RCU/rcu_dereference.rst | 27 | ||||
| -rw-r--r-- | Documentation/RCU/torture.rst | 2 |
3 files changed, 37 insertions, 17 deletions
diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst index bd3c58c44bef..2d42998a89a6 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 3b739f6243c8..659d5913784d 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 b3b6dfa85248..49e7beea6ae1 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:: |