Gilles Chanteperdrix wrote: > Gilles Chanteperdrix wrote: >> Jan Kiszka wrote: >>> Gilles Chanteperdrix wrote: >>>> Jan Kiszka wrote: >>>>> Hi Gilles, >>>>> >>>>> trying to understand the cb_read/write lock usage, some question came up >>>>> here: What prevents that the mutexq iteration in pse51_mutex_check_init >>>>> races against pse51_mutex_destroy_internal? >>>>> >>>>> If nothing, then I wonder if we actually have to iterate over the whole >>>>> queue to find out whether a given object has been initialized and >>>>> registered already or not. Can't this be encoded differently? >>>> We actually iterate over the queue only if the magic happens to be >>>> correct, which is not the common case. >>> However, there remains a race window with other threads removing other >>> mutex objects in parallel, changing the queue - risking a kernel oops. >>> And that is what worries me. It's unlikely. but possible. It's unclean. >> Ok. This used to be protected by the nklock. We should add the nklock again. > > Well I do not think that anyone is rescheduling, so we could probably > replace the nklock with a per-kqueue xnlock.
If nklock or per queue - both will introduce O(n) at least local preemption blocking. That's why I was asking for an alternative algorithm than iterating over the whole list. Jan
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