On Thu, Jun 20, 2013 at 04:59:29AM +0800, Liu Ping Fan wrote: > BH will be used outside big lock, so introduce lock to protect > between the writers, ie, bh's adders and deleter. The lock only > affects the writers and bh's callback does not take this extra lock. > Note that for the same AioContext, aio_bh_poll() can not run in > parallel yet. > > Signed-off-by: Liu Ping Fan <pingf...@linux.vnet.ibm.com> > --- > async.c | 22 ++++++++++++++++++++++ > include/block/aio.h | 5 +++++ > 2 files changed, 27 insertions(+)
qemu_bh_cancel() and qemu_bh_delete() are not modified by this patch. It seems that calling them from a thread is a little risky because there is no guarantee that the BH is no longer invoked after a thread calls these functions. I think that's worth a comment or do you want them to take the lock so they become safe? The other thing I'm unclear on is the ->idle assignment followed immediately by a ->scheduled assignment. Without memory barriers aio_bh_poll() isn't guaranteed to get an ordered view of these updates: it may see an idle BH as a regular scheduled BH because ->idle is still 0. Stefan
