On 06/03/20 14:50, Stefan Hajnoczi wrote: >> Not sure I understand the "almost" part. If it's accessed only from >> aio_poll() it is protected via either AIO_WAIT_WHILE or the BQL, not by >> ctx->list_lock; if it's protected by ctx->list_lock (using >> qemu_lockcnt_inc in readers), it is an RCU list. > aio_remove_fd_handler() removes nodes from the list during > aio_set_fd_handler(), but only while holding ctx->list_lock and the > count is zero (no readers). > > All other access is done from with ctx->list_lock incremented. This > code needs to be reentrant in case of nested aio_poll() but nothing else > will access the list at the same time.
Oh, I see, adds are only done under ctx->list_lock and those are the part that need the write barriers in the RCU iterators. Paolo > Therefore RCU is not needed. ctx->list_lock acts more like a rwlock.
