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[ Upstream commit62c07983be] 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 commit4c2c8f03a5("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> Signed-off-by: Sasha Levin <sashal@kernel.org>
86 lines
2.7 KiB
C
86 lines
2.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_ONCE_H
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#define _LINUX_ONCE_H
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#include <linux/types.h>
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#include <linux/jump_label.h>
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/* Helpers used from arbitrary contexts.
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* Hard irqs are blocked, be cautious.
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*/
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bool __do_once_start(bool *done, unsigned long *flags);
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void __do_once_done(bool *done, struct static_key_true *once_key,
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unsigned long *flags, struct module *mod);
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/* Variant for process contexts only. */
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bool __do_once_slow_start(bool *done);
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void __do_once_slow_done(bool *done, struct static_key_true *once_key,
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struct module *mod);
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/* Call a function exactly once. The idea of DO_ONCE() is to perform
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* a function call such as initialization of random seeds, etc, only
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* once, where DO_ONCE() can live in the fast-path. After @func has
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* been called with the passed arguments, the static key will patch
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* out the condition into a nop. DO_ONCE() guarantees type safety of
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* arguments!
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*
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* Note that the following is not equivalent ...
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*
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* DO_ONCE(func, arg);
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* DO_ONCE(func, arg);
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*
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* ... to this version:
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*
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* void foo(void)
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* {
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* DO_ONCE(func, arg);
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* }
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*
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* foo();
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* foo();
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*
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* In case the one-time invocation could be triggered from multiple
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* places, then a common helper function must be defined, so that only
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* a single static key will be placed there!
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*/
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#define DO_ONCE(func, ...) \
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({ \
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bool ___ret = false; \
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static bool __section(".data.once") ___done = false; \
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static DEFINE_STATIC_KEY_TRUE(___once_key); \
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if (static_branch_unlikely(&___once_key)) { \
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unsigned long ___flags; \
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___ret = __do_once_start(&___done, &___flags); \
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if (unlikely(___ret)) { \
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func(__VA_ARGS__); \
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__do_once_done(&___done, &___once_key, \
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&___flags, THIS_MODULE); \
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} \
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} \
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___ret; \
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})
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/* Variant of DO_ONCE() for process/sleepable contexts. */
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#define DO_ONCE_SLOW(func, ...) \
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({ \
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bool ___ret = false; \
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static bool __section(".data.once") ___done = false; \
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static DEFINE_STATIC_KEY_TRUE(___once_key); \
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if (static_branch_unlikely(&___once_key)) { \
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___ret = __do_once_slow_start(&___done); \
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if (unlikely(___ret)) { \
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func(__VA_ARGS__); \
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__do_once_slow_done(&___done, &___once_key, \
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THIS_MODULE); \
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} \
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} \
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___ret; \
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})
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#define get_random_once(buf, nbytes) \
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DO_ONCE(get_random_bytes, (buf), (nbytes))
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#define get_random_slow_once(buf, nbytes) \
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DO_ONCE_SLOW(get_random_bytes, (buf), (nbytes))
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#endif /* _LINUX_ONCE_H */
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