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once: add DO_ONCE_SLOW() for sleepable contexts

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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 4c2c8f03a5 ("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: 4c2c8f03a5 ("tcp: increase source port perturb table to 2^16")
Fixes: 190cc82489 ("tcp: change source port randomizarion at connect() time")
Reported-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/netdev/CANn89iLAEYBaoYajy0Y9UmGFff5GPxDUoG-ErVB2jDdRNQ5Tug@mail.gmail.com/T/#t
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2022-10-01 13:51:02 -07:00
committed by David S. Miller
parent f75886a045
commit 62c07983be
3 changed files with 60 additions and 2 deletions
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30
lib/once.c
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@@ -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);