random: remove kernel.random.read_wakeup_threshold

commit c95ea0c69f upstream.

It has no effect any more, so remove it.  We can revert this if
there is some user code that expects to be able to set this sysctl.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/a74ed2cf0b5a5451428a246a9239f5bc4e29358f.1577088521.git.luto@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/random.c

@@ -370,12 +370,6 @@
 #define ENTROPY_SHIFT 3
 #define ENTROPY_BITS(r) ((r)->entropy_count >> ENTROPY_SHIFT)
 
-/*
- * The minimum number of bits of entropy before we wake up a read on
- * /dev/random.  Should be enough to do a significant reseed.
- */
-static int random_read_wakeup_bits = 64;
-
 /*
  * If the entropy count falls under this number of bits, then we
  * should wake up processes which are selecting or polling on write
@@ -2012,8 +2006,7 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
 
 #include <linux/sysctl.h>
 
-static int min_read_thresh = 8, min_write_thresh;
-static int max_read_thresh = OUTPUT_POOL_WORDS * 32;
+static int min_write_thresh;
 static int max_write_thresh = INPUT_POOL_WORDS * 32;
 static int random_min_urandom_seed = 60;
 static char sysctl_bootid[16];
@@ -2088,15 +2081,6 @@ struct ctl_table random_table[] = {
 		.proc_handler	= proc_do_entropy,
 		.data		= &input_pool.entropy_count,
 	},
-	{
-		.procname	= "read_wakeup_threshold",
-		.data		= &random_read_wakeup_bits,
-		.maxlen		= sizeof(int),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &min_read_thresh,
-		.extra2		= &max_read_thresh,
-	},
 	{
 		.procname	= "write_wakeup_threshold",
 		.data		= &random_write_wakeup_bits,