random: forget lock in lockless accounting

The only mutable data accessed here is ->entropy_count, but since
10b3a32d ("random: fix accounting race condition") we use cmpxchg to
protect our accesses to ->entropy_count here.  Drop the use of the
lock.

Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Price <price@mit.edu>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

drivers/char/random.c

@@ -970,9 +970,6 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
 	int entropy_count, orig;
 	size_t ibytes;
 
-	/* Hold lock while accounting */
-	spin_lock_irqsave(&r->lock, flags);
-
 	BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
 
 	/* Can we pull enough? */
@@ -995,7 +992,6 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
 		    < random_write_wakeup_thresh)
 			wakeup_write = 1;
 	}
-	spin_unlock_irqrestore(&r->lock, flags);
 
 	trace_debit_entropy(r->name, 8 * ibytes);
 	if (wakeup_write) {