On Fri, Mar 06, 2020 at 03:17:40PM +0100, Paolo Bonzini wrote: > 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.
I'll update the comment when merging this series. Stefan
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