Messages in this thread | | | From | "Christian Ehrhardt" <> | Date | Sat, 31 Aug 2002 19:31:07 +0200 | Subject | Re: 2.5.32: DEBUG_SLAB and PREEMPT = constant oops in schedule() |
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On Fri, Aug 30, 2002 at 09:06:38AM +0200, Ingo Molnar wrote: > > On Thu, 29 Aug 2002, Christian Ehrhardt wrote: > > > sys_sched_setaffinity, lines: > > 1571 get_task_struct(p); > > 1572 read_unlock(&tasklist_lock); > > > Line 1571 calls get_task_struct because the task might exit during the > > syscall. Suppose that this is exactly what happens. This means that line > > 1583 will effectivly free the task. But set_cpus_allowed stuffed a > > pointer to the task into a request struct without incrementing the usage > > count of the task struct. > > note that the scenario you describe is not possible, because > set_cpus_allowed() will wait for the migration thread to do its work - so > the put_task_struct can never come before the last use of the task > structure. See the 'down(&req.sem)' in set_cpus_allowed(), and the > up(&req->sem) in migration_thread().
Agreed. Is there anything that prevents the other scenario described in the original mail, i.e. sys_wait frees the task struct before the task finally scheduled away? There used to be a lock_kernel in sys_wait and sys_exit to make sure this doesn't happen but it is gone in 2.5.
regards Christian
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