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Subject[PATCH 3/7] static_key: keep deferred enabled counter debt
Date
When '.enabled.counter == 1', static_key_slow_dec_deferred() gets
silently dropped if the decrease is already pending.

We print a warning if this happens and because .enabled.counter cannot
go below 1 before the decrease has finished, the number of ignored
static_key_slow_dec_deferred() is kept and we skip an equal amount of
static_key_slow_inc_deferred().

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
atomic_dec_if_positive() is weird ...

include/linux/jump_label_ratelimit.h | 1 +
kernel/jump_label.c | 17 +++++++++++------
2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/include/linux/jump_label_ratelimit.h b/include/linux/jump_label_ratelimit.h
index e2fa2e7..e3a7a83 100644
--- a/include/linux/jump_label_ratelimit.h
+++ b/include/linux/jump_label_ratelimit.h
@@ -9,6 +9,7 @@ struct static_key_deferred {
struct static_key key;
unsigned long timeout;
struct delayed_work work;
+ atomic_t enabled_debt;
};
#endif

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index ff67257..30aa3b0 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -75,13 +75,15 @@ EXPORT_SYMBOL_GPL(static_key_slow_inc);

void static_key_slow_inc_deferred(struct static_key_deferred *key)
{
+ if (atomic_dec_if_positive(&key->enabled_debt) >= 0)
+ return;
if (!cancel_delayed_work(&key->work))
static_key_slow_inc(&key->key);
}
EXPORT_SYMBOL_GPL(static_key_slow_inc_deferred);

static void __static_key_slow_dec(struct static_key *key,
- unsigned long rate_limit, struct delayed_work *work)
+ struct static_key_deferred *dkey)
{
if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
WARN(atomic_read(&key->enabled) < 0,
@@ -89,9 +91,12 @@ static void __static_key_slow_dec(struct static_key *key,
return;
}

- if (rate_limit) {
+ if (dkey && dkey->timeout) {
atomic_inc(&key->enabled);
- schedule_delayed_work(work, rate_limit);
+ if (!schedule_delayed_work(&dkey->work, dkey->timeout)) {
+ atomic_inc(&dkey->enabled_debt);
+ WARN(1, "jump label: negative deferred count!\n");
+ }
} else {
if (!jump_label_get_branch_default(key))
jump_label_update(key, JUMP_LABEL_DISABLE);
@@ -105,18 +110,18 @@ static void jump_label_update_timeout(struct work_struct *work)
{
struct static_key_deferred *key =
container_of(work, struct static_key_deferred, work.work);
- __static_key_slow_dec(&key->key, 0, NULL);
+ __static_key_slow_dec(&key->key, NULL);
}

void static_key_slow_dec(struct static_key *key)
{
- __static_key_slow_dec(key, 0, NULL);
+ __static_key_slow_dec(key, NULL);
}
EXPORT_SYMBOL_GPL(static_key_slow_dec);

void static_key_slow_dec_deferred(struct static_key_deferred *key)
{
- __static_key_slow_dec(&key->key, key->timeout, &key->work);
+ __static_key_slow_dec(&key->key, key);
}
EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);

--
1.8.3.1
--
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