tree 9d4f1ecda408dcbb34642d530bdd9837f877abcc
parent 8755f50ce5ff3bc644332b7c235da12cf942a24f
author Barret Rhoden <brho@cs.berkeley.edu> 1532034894 -0400
committer Barret Rhoden <brho@cs.berkeley.edu> 1532035312 -0400

rcu: Panic if a call_rcu() CB blocks

RCU callbacks are not allowed to block.  Here's what Linux has to say:

	... the callback function must be written to be called from softirq
	context.  In particular, it cannot block.

Same goes for us.  If a CB blocks, then all further CBs will be blocked
too, and the code that will wake up the first CB could also be blocked on a
later CB.

Note the distinction between RCU callbacks and RCU threads.  The threads
are critical parts of implementing RCU; they are never allowed to block on
RCU primitives.  Yes, any RCU callback will be run by an RCU thread, but
the problem is slightly different.

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>