On 09/11/2012 12:44 PM, liu ping fan wrote: > On Tue, Sep 11, 2012 at 4:35 PM, Avi Kivity <a...@redhat.com> wrote: >> On 09/11/2012 10:51 AM, Liu Ping Fan wrote: >>> From: Liu Ping Fan <pingf...@linux.vnet.ibm.com> >>> >>> The func call chain can suffer from recursively hold >>> qemu_mutex_lock_iothread. We introduce lockmap to record the >>> lock depth. >> >> What is the root cause? io handlers initiating I/O? >> > cpu_physical_memory_rw() can be called nested, and when called, it can > be protected by no-lock/device lock/ big-lock.
Then we should look for a solution that is local to exec.c (and the nested dispatch problem). I think we can identify and fix all nested dispatches (converting them to either async dma, or letting the memory core do a single dispatch without indirection through I/O handlers). > I think without big lock, io-dispatcher should face the same issue. > As to main-loop, have not carefully consider, but at least, dma-helper > will call cpu_physical_memory_rw() with big-lock. DMA is inherently asynchronous, so we already drop the lock between initiation and completion; we need to find a way to make it easy to use the API without taking the lock while the transfer takes place. -- error compiling committee.c: too many arguments to function
