Messages in this thread | | | From | Manfred Spraul <> | Subject | [PATCH 0/7 V6] Clarify/standardize memory barriers for lock/unlock | Date | Thu, 1 Sep 2016 17:04:10 +0200 |
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Hi,
Based on the new consensus: - spin_unlock_wait() is spin_lock();spin_unlock(); - no guarantees are provided by spin_is_locked(). - the acquire during spin_lock() is for the load, not for the store.
Summary: If a high-scalability locking scheme is built with multiple spinlocks, then often additional memory barriers are required.
The documentation was not as clear as possible, and memory barriers were missing / superfluous in the implementation.
Patch 1: sem.c: Remove the smp_rmb() after spin_unlock_wait(). Patch 2: Documentation Patch 3: Update ipc/sem.c based on rules above Patch 4: Move smp_mb__after_unlock_lock to <linux/spinlock.h> Patch 5: Fix memory ordering for nf_conntrack Patch 6: nf_conntrack: Remove smp_rmb() after spin_unlock_wait() Patch 7: nf_conntrack: Remove smp_mb() after spin_lock().
Patch 5 is larger than required, it rewrites the conntrack logic with the code from ipc/sem.c. I think the new code is simpler and more realtime-friendly.
@netfilter team: Over which tree should the patch be sent? Usually, I ask Andrew to merge my patches (as there is no maintainer tree for ipc).
@Andrew: The patches are relative to mmots. Could you include them in your tree, with the target of including in linux-next?
-- Manfred
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