umtx: Add bitset member to the struct umtx_q.

[dchagin]

Summary

Bitset is a Linux emulation layer extension. This 32-bit mask, in which at least
one bit must be set, is used to select which threads should be woken up.

[dchagin]

followup D31248

[markj]

sys/kern/kern_umtx.c

573

Why is it hard-coded to SHARED_QUEUE?

sys/sys/umtxvar.h

122–125

There is a hole here on LP64, if you add the new field here the size of the structure will not grow.

[dchagin]

sys/kern/kern_umtx.c

573

EXCLUSIVE_QUEUE used only by rw_lock, many umtx functions hide queue, umtxq_insert/umtxq_remove pair for example

sys/sys/umtxvar.h

122–125

good, thanks, will fix it

[dchagin]

done

[kib]

sys/kern/kern_umtx.c

574

if (uf == NULL)
  return (0);

Then decrease indent level by one.

575

I do not know the intent, but what if there is a hole in the queue WRT bitmask? I mean, e.g. if we have thee elements with the uq_bitset values 1, 2, 4, and bitset is 5. Then you miss the element 4.

sys/sys/umtxvar.h

124

If the field is 32bit mask, then might be uint32_t type is better? It is explicit.

[dchagin]

whoops, perhaps I fixed it

[dchagin]

s/u_int/uint32_t/