random: quiet urandom warning ratelimit suppression message

random.c ratelimits how much it warns about uninitialized urandom reads
using __ratelimit(). When the RNG is finally initialized, it prints the
number of missed messages due to ratelimiting.

It has been this way since that functionality was introduced back in
2018. Recently, cc1e127b ("random: remove ratelimiting for in-kernel
unseeded randomness") put a bit more stress on the urandom ratelimiting,
which teased out a bug in the implementation.

Specifically, when under pressure, __ratelimit() will print its own
message and reset the count back to 0, making the final message at the
end less useful. Secondly, it does so as a pr_warn(), which apparently
is undesirable for people's CI.

Fortunately, __ratelimit() has the RATELIMIT_MSG_ON_RELEASE flag exactly
for this purpose, so we set the flag.

Fixes: 4e00b339 ("random: rate limit unseeded randomness warnings")
Cc: stable@vger.kernel.org
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Reported-by: Ron Economos <re@w6rz.net>
Tested-by: Ron Economos <re@w6rz.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

drivers/char/random.c

@@ -87,7 +87,7 @@ static struct fasync_struct *fasync;
 
 /* Control how we warn userspace. */
 static struct ratelimit_state urandom_warning =
-	RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
+	RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
 static int ratelimit_disable __read_mostly =
 	IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);

include/linux/ratelimit_types.h

@@ -23,12 +23,16 @@ struct ratelimit_state {
 	unsigned long	flags;
 };
 
-#define RATELIMIT_STATE_INIT(name, interval_init, burst_init) {		\
-		.lock		= __RAW_SPIN_LOCK_UNLOCKED(name.lock),	\
-		.interval	= interval_init,			\
-		.burst		= burst_init,				\
+#define RATELIMIT_STATE_INIT_FLAGS(name, interval_init, burst_init, flags_init) { \
+		.lock		= __RAW_SPIN_LOCK_UNLOCKED(name.lock),		  \
+		.interval	= interval_init,				  \
+		.burst		= burst_init,					  \
+		.flags		= flags_init,					  \
 	}
 
+#define RATELIMIT_STATE_INIT(name, interval_init, burst_init) \
+	RATELIMIT_STATE_INIT_FLAGS(name, interval_init, burst_init, 0)
+
 #define RATELIMIT_STATE_INIT_DISABLED					\
 	RATELIMIT_STATE_INIT(ratelimit_state, 0, DEFAULT_RATELIMIT_BURST)