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Commit 131287ff authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman
Browse files

once: add DO_ONCE_SLOW() for sleepable contexts 



[ Upstream commit 62c07983bef9d3e78e71189441e1a470f0d1e653 ]

Christophe Leroy reported a ~80ms latency spike
happening at first TCP connect() time.

This is because __inet_hash_connect() uses get_random_once()
to populate a perturbation table which became quite big
after commit 4c2c8f03a5ab ("tcp: increase source port perturb table to 2^16")

get_random_once() uses DO_ONCE(), which block hard irqs for the duration
of the operation.

This patch adds DO_ONCE_SLOW() which uses a mutex instead of a spinlock
for operations where we prefer to stay in process context.

Then __inet_hash_connect() can use get_random_slow_once()
to populate its perturbation table.

Fixes: 4c2c8f03a5ab ("tcp: increase source port perturb table to 2^16")
Fixes: 190cc82489f4 ("tcp: change source port randomizarion at connect() time")
Reported-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/netdev/CANn89iLAEYBaoYajy0Y9UmGFff5GPxDUoG-ErVB2jDdRNQ5Tug@mail.gmail.com/T/#t


Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Tested-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 03ac583e

include/linux/once.h

+28 −0
Original line number Diff line number Diff line
@@ -5,10 +5,18 @@ 
#include <linux/types.h>

#include <linux/jump_label.h>



/* Helpers used from arbitrary contexts.

 * Hard irqs are blocked, be cautious.

 */

bool __do_once_start(bool *done, unsigned long *flags);

void __do_once_done(bool *done, struct static_key_true *once_key,

		    unsigned long *flags, struct module *mod);



/* Variant for process contexts only. */

bool __do_once_slow_start(bool *done);

void __do_once_slow_done(bool *done, struct static_key_true *once_key,

			 struct module *mod);



/* Call a function exactly once. The idea of DO_ONCE() is to perform

 * a function call such as initialization of random seeds, etc, only

 * once, where DO_ONCE() can live in the fast-path. After @func has
@@ -52,9 +60,29 @@ void __do_once_done(bool *done, struct static_key_true *once_key, 
		___ret;							     \

	})



/* Variant of DO_ONCE() for process/sleepable contexts. */

#define DO_ONCE_SLOW(func, ...)						     \

	({								     \

		bool ___ret = false;					     \

		static bool __section(".data.once") ___done = false;	     \

		static DEFINE_STATIC_KEY_TRUE(___once_key);		     \

		if (static_branch_unlikely(&___once_key)) {		     \

			___ret = __do_once_slow_start(&___done);	     \

			if (unlikely(___ret)) {				     \

				func(__VA_ARGS__);			     \

				__do_once_slow_done(&___done, &___once_key,  \

						    THIS_MODULE);	     \

			}						     \

		}							     \

		___ret;							     \

	})



#define get_random_once(buf, nbytes)					     \

	DO_ONCE(get_random_bytes, (buf), (nbytes))

#define get_random_once_wait(buf, nbytes)                                    \

	DO_ONCE(get_random_bytes_wait, (buf), (nbytes))                      \



#define get_random_slow_once(buf, nbytes)				     \

	DO_ONCE_SLOW(get_random_bytes, (buf), (nbytes))



#endif /* _LINUX_ONCE_H */

lib/once.c

+30 −0
Original line number Diff line number Diff line
@@ -66,3 +66,33 @@ void __do_once_done(bool *done, struct static_key_true *once_key, 
	once_disable_jump(once_key, mod);

}

EXPORT_SYMBOL(__do_once_done);



static DEFINE_MUTEX(once_mutex);



bool __do_once_slow_start(bool *done)

	__acquires(once_mutex)

{

	mutex_lock(&once_mutex);

	if (*done) {

		mutex_unlock(&once_mutex);

		/* Keep sparse happy by restoring an even lock count on

		 * this mutex. In case we return here, we don't call into

		 * __do_once_done but return early in the DO_ONCE_SLOW() macro.

		 */

		__acquire(once_mutex);

		return false;

	}



	return true;

}

EXPORT_SYMBOL(__do_once_slow_start);



void __do_once_slow_done(bool *done, struct static_key_true *once_key,

			 struct module *mod)

	__releases(once_mutex)

{

	*done = true;

	mutex_unlock(&once_mutex);

	once_disable_jump(once_key, mod);

}

EXPORT_SYMBOL(__do_once_slow_done);

net/ipv4/inet_hashtables.c

+2 −2
Original line number Diff line number Diff line
@@ -725,7 +725,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row, 
	if (likely(remaining > 1))

		remaining &= ~1U;



	net_get_random_once(table_perturb,

	get_random_slow_once(table_perturb,

			     INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb));

	index = port_offset & (INET_TABLE_PERTURB_SIZE - 1);