On 26/09/2016 09:28, Alex Bennée wrote: > > cpu->running is only read under the mutex, but can be written _by the > > owner thread only_ outside the mutex. So writes outside the mutex must > > be atomic, but writes under the mutex don't because: > > > > - no other thread ever writes to cpu->running > > > > - no other thread can be reading cpu->running > > Should we add some comments to cpu.h's definitions to make the rules clear?
I don't know... It's awfully easy for such documentation to get out of date. Currently it says: * @running: #true if CPU is currently running (lockless). * @has_waiter: #true if a CPU is currently waiting for the cpu_exec_end; * valid under cpu_list_lock. I think it's a good middle ground; it's kind of obvious that only the CPU itself writes cpu->running. I'm changing anyway the cpu->running assignment to atomic_set as suggested by Richard, and that makes it valid to read cpu->running outside the lock. Paolo
