diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-08-08 08:59:54 +0400 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-08-20 20:00:10 +0400 |
| commit | 9079fd7c2e06a92cf27d05224a1f478581916c5b (patch) | |
| tree | 9f093e0efc716c18c3ca66fbd670e3f1099e4fe6 /include/linux/rcupdate.h | |
| parent | a57eb940d130477a799dfb24a570ee04979c0f7f (diff) | |
| download | linux-9079fd7c2e06a92cf27d05224a1f478581916c5b.tar.xz | |
rcu: update obsolete rcu_read_lock() comment.
The comment says that blocking is illegal in rcu_read_lock()-style
RCU read-side critical sections, which is no longer entirely true
given preemptible RCU. This commit provides a fix.
Suggested-by: David Miller <davem@davemloft.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'include/linux/rcupdate.h')
| -rw-r--r-- | include/linux/rcupdate.h | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 24b896649384..d7af96ef6fcf 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -458,7 +458,20 @@ extern int rcu_my_thread_group_empty(void); * will be deferred until the outermost RCU read-side critical section * completes. * - * It is illegal to block while in an RCU read-side critical section. + * You can avoid reading and understanding the next paragraph by + * following this rule: don't put anything in an rcu_read_lock() RCU + * read-side critical section that would block in a !PREEMPT kernel. + * But if you want the full story, read on! + * + * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it + * is illegal to block while in an RCU read-side critical section. In + * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) + * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may + * be preempted, but explicit blocking is illegal. Finally, in preemptible + * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, + * RCU read-side critical sections may be preempted and they may also + * block, but only when acquiring spinlocks that are subject to priority + * inheritance. */ static inline void rcu_read_lock(void) { |