once: add DO_ONCE_SLOW() for sleepable contexts

stable inclusion
from stable-v4.19.262
commit f5686a03b138f6330eeda082ee4f96c8109f56f3
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ZXGL


CVE: NA

--------------------------------

[ Upstream commit 62c07983 ]

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 4c2c8f03 ("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: 4c2c8f03 ("tcp: increase source port perturb table to 2^16")
Fixes: 190cc824 ("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>

One conflict occurs because the commit 4c2c8f03 ("tcp: increase
source port perturb table to 2^16") is integrated but the commit
e9261476 ("tcp: dynamically allocate the perturb table used by
source port") is not integrated.
One conflict occurs because the commit 1027b96e ("once: Fix panic
when module unload") is not integrated.

Conflicts:
	net/ipv4/inet_hashtables.c
	lib/once.c

Signed-off-by: Liu Jian <liujian56@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>