rcu: update obsolete rcu_read_lock() comment.
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 <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>
Signed-off-by: Paul E. McKenney <1e0ce936bb9b355d257bf5790d2513c3f28be22b@linux.vnet.ibm.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs