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Commit 9079fd7c authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarDavid Miller <davem@davemloft.net>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent a57eb940

include/linux/rcupdate.h

+14 −1
Original line number Diff line number Diff line
@@ -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)

{