On 05/10/2016 15:13, Stefan Hajnoczi wrote: > > qemu_bh_delete is already clearing bh->scheduled at the same time > > as it's setting bh->deleted. Since it's not using any memory > > barriers, there is no synchronization going on for bh->deleted, > > and this makes the bh->deleted checks superfluous in aio_compute_timeout, > > aio_bh_poll and aio_ctx_check. > > Yikes. On one hand this sounds scary but in practice qemu_bh_delete() > isn't called from another thread so the next aio_bh_poll() will indeed > clean it up instead of dispatching a deleted BH. > > Due to the nature of this change I suggest making it in a separate > patch.
Separate from what? (Sorry if I'm being dense). >> >> + * aio_bh_schedule_oneshot: Allocate a new bottom half structure that will >> run >> + * only once and as soon as possible. >> + * >> + * Bottom halves are lightweight callbacks whose invocation is guaranteed >> + * to be wait-free, thread-safe and signal-safe. The #QEMUBH structure >> + * is opaque and must be allocated prior to its use. > > I'm confused. There is no QEMUBH structure in this function > prototype. Is this comment from an earlier version of this function? No, it's from aio_bh_new. Of course this one is neither wait-free nor signal-safe. Kevin, do you want me to respin? Paolo
