From: "Joel Fernandes (Google)" <[email protected]> This commit updates the documentation with information about usage of lockdep with list_for_each_entry_rcu().
Signed-off-by: Joel Fernandes (Google) <[email protected]> [ paulmck: Wordsmithing. ] Signed-off-by: Paul E. McKenney <[email protected]> --- Documentation/RCU/lockdep.txt | 18 ++++++++++++++---- Documentation/RCU/whatisRCU.txt | 10 +++++++++- 2 files changed, 23 insertions(+), 5 deletions(-) diff --git a/Documentation/RCU/lockdep.txt b/Documentation/RCU/lockdep.txt index da51d30..89db949e 100644 --- a/Documentation/RCU/lockdep.txt +++ b/Documentation/RCU/lockdep.txt @@ -96,7 +96,17 @@ other flavors of rcu_dereference(). On the other hand, it is illegal to use rcu_dereference_protected() if either the RCU-protected pointer or the RCU-protected data that it points to can change concurrently. -There are currently only "universal" versions of the rcu_assign_pointer() -and RCU list-/tree-traversal primitives, which do not (yet) check for -being in an RCU read-side critical section. In the future, separate -versions of these primitives might be created. +Like rcu_dereference(), when lockdep is enabled, RCU list and hlist +traversal primitives check for being called from within an RCU read-side +critical section. However, a lockdep expression can be passed to them +as a additional optional argument. With this lockdep expression, these +traversal primitives will complain only if the lockdep expression is +false and they are called from outside any RCU read-side critical section. + +For example, the workqueue for_each_pwq() macro is intended to be used +either within an RCU read-side critical section or with wq->mutex held. +It is thus implemented as follows: + + #define for_each_pwq(pwq, wq) + list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node, + lock_is_held(&(wq->mutex).dep_map)) diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 17f4831..58ba05c 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -290,7 +290,7 @@ rcu_dereference() at any time, including immediately after the rcu_dereference(). And, again like rcu_assign_pointer(), rcu_dereference() is typically used indirectly, via the _rcu list-manipulation - primitives, such as list_for_each_entry_rcu(). + primitives, such as list_for_each_entry_rcu() [2]. [1] The variant rcu_dereference_protected() can be used outside of an RCU read-side critical section as long as the usage is @@ -305,6 +305,14 @@ rcu_dereference() a lockdep splat is emitted. See Documentation/RCU/Design/Requirements/Requirements.rst and the API's code comments for more details and example usage. + [2] If the list_for_each_entry_rcu() instance might be used by + update-side code as well as by RCU readers, then an additional + lockdep expression can be added to its list of arguments. + For example, given an additional "lock_is_held(&mylock)" argument, + the RCU lockdep code would complain only if this instance was + invoked outside of an RCU read-side critical section and without + the protection of mylock. + The following diagram shows how each API communicates among the reader, updater, and reclaimer. -- 2.9.5
