On Sun, Jun 27, 2021 at 06:19:18PM +0200, Manfred Spraul wrote: > KCSAN detected an data race with ipc/sem.c that is intentional. > > As nf_conntrack_lock() uses the same algorithm: Update > nf_conntrack_core as well: > > nf_conntrack_lock() contains > a1) spin_lock() > a2) smp_load_acquire(nf_conntrack_locks_all). > > a1) actually accesses one lock from an array of locks. > > nf_conntrack_locks_all() contains > b1) nf_conntrack_locks_all=true (normal write) > b2) spin_lock() > b3) spin_unlock() > > b2 and b3 are done for every lock. > > This guarantees that nf_conntrack_locks_all() prevents any > concurrent nf_conntrack_lock() owners: > If a thread past a1), then b2) will block until that thread releases > the lock. > If the threat is before a1, then b3)+a1) ensure the write b1) is > visible, thus a2) is guaranteed to see the updated value. > > But: This is only the latest time when b1) becomes visible. > It may also happen that b1) is visible an undefined amount of time > before the b3). And thus KCSAN will notice a data race. > > In addition, the compiler might be too clever. > > Solution: Use WRITE_ONCE(). Applied, thanks.
