In mem cgroup, we need to guarantee that two concurrent updates of the jump_label interface wait for each other. IOW, we can't have other updates returning while the first one is still patching the kernel around, otherwise we'll race.
I believe this is something that can fit well in the static branch API, without noticeable disadvantages: * in the common case, it will be a quite simple lock/unlock operation * Every context that calls static_branch_slow* already expects to be in sleeping context because it will mutex_lock the unlikely case. * static_key_slow_inc is not expected to be called in any fast path, otherwise it would be expected to have quite a different name. Therefore the mutex + atomic combination instead of just an atomic should not kill us. Signed-off-by: Glauber Costa <[email protected]> CC: Tejun Heo <[email protected]> CC: Li Zefan <[email protected]> CC: Kamezawa Hiroyuki <[email protected]> CC: Johannes Weiner <[email protected]> CC: Michal Hocko <[email protected]> CC: Ingo Molnar <[email protected]> CC: Jason Baron <[email protected]> --- kernel/jump_label.c | 21 +++++++++++---------- 1 files changed, 11 insertions(+), 10 deletions(-) diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 4304919..5d09cb4 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -57,17 +57,16 @@ static void jump_label_update(struct static_key *key, int enable); void static_key_slow_inc(struct static_key *key) { + jump_label_lock(); if (atomic_inc_not_zero(&key->enabled)) - return; + goto out; - jump_label_lock(); - if (atomic_read(&key->enabled) == 0) { - if (!jump_label_get_branch_default(key)) - jump_label_update(key, JUMP_LABEL_ENABLE); - else - jump_label_update(key, JUMP_LABEL_DISABLE); - } + if (!jump_label_get_branch_default(key)) + jump_label_update(key, JUMP_LABEL_ENABLE); + else + jump_label_update(key, JUMP_LABEL_DISABLE); atomic_inc(&key->enabled); +out: jump_label_unlock(); } EXPORT_SYMBOL_GPL(static_key_slow_inc); @@ -75,10 +74,11 @@ EXPORT_SYMBOL_GPL(static_key_slow_inc); static void __static_key_slow_dec(struct static_key *key, unsigned long rate_limit, struct delayed_work *work) { - if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) { + jump_label_lock(); + if (atomic_dec_and_test(&key->enabled)) { WARN(atomic_read(&key->enabled) < 0, "jump label: negative count!\n"); - return; + goto out; } if (rate_limit) { @@ -90,6 +90,7 @@ static void __static_key_slow_dec(struct static_key *key, else jump_label_update(key, JUMP_LABEL_ENABLE); } +out: jump_label_unlock(); } -- 1.7.7.6 _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
