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once: add DO_ONCE_SLOW() for sleepable contexts

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[ 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: 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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Eric Dumazet
2022-10-01 13:51:02 -07:00
committed by Greg Kroah-Hartman
parent 67cb80a9d2
commit 6cb54f2162
3 changed files with 60 additions and 2 deletions
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4
net/ipv4/inet_hashtables.c
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@@ -771,8 +771,8 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
if (likely(remaining > 1))
remaining &= ~1U;
net_get_random_once(table_perturb,
INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb));
get_random_slow_once(table_perturb,
INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb));
index = port_offset & (INET_TABLE_PERTURB_SIZE - 1);
offset = READ_ONCE(table_perturb[index]) + (port_offset >> 32);