From: Eric Dumazet
[ 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
Link:
https://lore.kernel.org/netdev/cann89ilaeybaoyajy0y9umgfff5gpxduog-ervb2jddrnq5...@mail.gmail.com/T/#t
Signed-off-by: Eric Dumazet
Cc: Willy Tarreau
Tested-by: Christophe Leroy
Signed-off-by: David S. Miller
Signed-off-by: Sasha Levin
Signed-off-by: Christophe Leroy
---
include/linux/once.h | 28
lib/once.c | 30 ++
net/ipv4/inet_hashtables.c | 4 ++--
3 files changed, 60 insertions(+), 2 deletions(-)
diff --git a/include/linux/once.h b/include/linux/once.h
index 6790884d3c57..bb091119b754 100644
--- a/include/linux/once.h
+++ b/include/linux/once.h
@@ -5,10 +5,18 @@
#include
#include
+/* 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 *once_key,
unsigned long *flags);
+/* Variant for process contexts only. */
+bool __do_once_slow_start(bool *done);
+void __do_once_slow_done(bool *done, struct static_key *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 *once_key,
___ret; \
})
+/* Variant of DO_ONCE() for process/sleepable contexts. */
+#define DO_ONCE_SLOW(func, ...)
\
+ ({ \
+ bool ___ret = false; \
+ static bool ___done = false; \
+ static struct static_key ___once_key = STATIC_KEY_INIT_TRUE; \
+ if (static_key_true(&___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 */
diff --git a/lib/once.c b/lib/once.c
index bfb7420d0de3..76c7bbc0aa40 100644
--- a/lib/once.c
+++ b/lib/once.c
@@ -61,3 +61,33 @@ void __do_once_done(bool *done, struct static_key *once_key,
once_disable_jump(once_key);
}
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 *once_key,
+struct module *mod
