Am 05.10.2016 um 15:55 hat Paolo Bonzini geschrieben: > 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?
If the comment is wrong, either post a v2 of this patch or just reply with a new version of the comment and I'll squash it in. Your choice, I don't mind either way. Kevin
