random: remove preempt disabled region

Ingo Molnar · tytso · commit b34fbaa92893 · 2018-07-24T15:44:32.000-04:00
No need to keep preemption disabled across the whole function. mix_pool_bytes() uses a spin_lock() to protect the pool and there are other places like write_pool() whhich invoke mix_pool_bytes() without disabling preemption. credit_entropy_bits() is invoked from other places like add_hwgenerator_randomness() without disabling preemption. Before commit 95b709b ("random: drop trickle mode") the function used __this_cpu_inc_return() which would require disabled preemption. The preempt_disable() section was added in commit 43d5d30 ("[PATCH] random driver preempt robustness", history tree). It was claimed that the code relied on "vt_ioctl() being called under BKL". Cc: "Theodore Ts'o" <tytso@mit.edu> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> [bigeasy: enhance the commit message] Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/drivers/char/random.c b/drivers/char/random.c
@@ -1131,8 +1131,6 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 	} sample;
 	long delta, delta2, delta3;
 
-	preempt_disable();
-
 	sample.jiffies = jiffies;
 	sample.cycles = random_get_entropy();
 	sample.num = num;
@@ -1170,8 +1168,6 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 	 * and limit entropy entimate to 12 bits.
 	 */
 	credit_entropy_bits(r, min_t(int, fls(delta>>1), 11));
-
-	preempt_enable();
 }
 
 void add_input_randomness(unsigned int type, unsigned int code,
