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authorEric Dumazet <edumazet@google.com>2022-10-01 13:51:02 -0700
committerDavid S. Miller <davem@davemloft.net>2022-10-03 13:29:11 +0100
commit62c07983bef9d3e78e71189441e1a470f0d1e653 (patch)
treef0ad523a6d93dcb8da22283a69298bbe16036083 /lib/once.c
parentf75886a045531fedf4c11cf06d977a91f4cb266c (diff)
downloadlwn-62c07983bef9d3e78e71189441e1a470f0d1e653.tar.gz
lwn-62c07983bef9d3e78e71189441e1a470f0d1e653.zip
once: add DO_ONCE_SLOW() for sleepable contexts
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>
Diffstat (limited to 'lib/once.c')
-rw-r--r--lib/once.c30
1 files changed, 30 insertions, 0 deletions
diff --git a/lib/once.c b/lib/once.c
index 59149bf3bfb4..351f66aad310 100644
--- a/lib/once.c
+++ b/lib/once.c
@@ -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);