> I profiled all executions of > qemu_mutex_lock_iothread(), and found that > it only protects the vl.c:main_loop_wai() thread but does NOT protect > the qemu-kvm.c:kvm_cpu_exec() thread. Did I miss something or is this > a defect? Hi again, I took another look at qemu-kvm 0.12.3 and here is how I read it: The mutex which is supposed to protect IO emulation is qemu-kvm.c:qemu_mutex. The cpu thread will unlock qemu_mutex in pre_kvm_run() before ioctl(fd, KVM_RUN, 0). Then it will lock qemu_mutex again in post_kvm_run(). The io thread will unlock qemu_mutex via qemu-kvm.c:qemu_mutex_unlock_iothread() before waiting in select(). Then it will lock qemu_mutex again in qemu-kvm.c:qemu_mutex_lock_iothread(). I believe this *does* protect IO emulation correctly. The code is confusing because there are multiple definitions of the same functions and #ifdefs, maybe I made a mistake. > Here is the trace showing that > qemu_mutex_lock_iothread() does not protect the thread > that executes. kvm_cpu_exec()->...->qcow_aio_write_cb(). > > home/ctang/kvm/qemu-kvm-0.12.3/qemu-kvm.c : 2530 thread: b7e056d0 > /home/ctang/kvm/bin/qemu-system-x86_64(qemu_mutex_unlock_iothread+0x1a) > [0x8092242] > /home/ctang/kvm/bin/qemu-system-x86_64(main_loop_wait+0x221) [0x806edef] > /home/ctang/kvm/bin/qemu-system-x86_64(kvm_main_loop+0x1ff) [0x80916a1] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x806f5c2] > /home/ctang/kvm/bin/qemu-system-x86_64(main+0x2e2c) [0x80736d1] > /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe5) [0xb7e33775] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x8068bb1] > > block/qcow2-cluster.c : 721 thread: b7dc2b90 > /home/ctang/kvm/bin/qemu-system-x86_64(qcow2_alloc_cluster_offset+0x3c) > [0x81175fa] > /home/ctang/kvm/bin/qemu-system-x86_64(qcow_aio_write_cb+0x158) > [0x8111d73] > /home/ctang/kvm/bin/qemu-system-x86_64(qcow_aio_writev+0x94) [0x8112054] > /home/ctang/kvm/bin/qemu-system-x86_64(bdrv_aio_writev+0xe1) [0x80fa8e9] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x81f4a96] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x81f4c04] > /home/ctang/kvm/bin/qemu-system-x86_64(dma_bdrv_write+0x48) [0x81f4cbf] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x80a437c] > /home/ctang/kvm/bin/qemu-system-x86_64(bmdma_cmd_writeb+0x73) > [0x80a9503] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x812b1eb] > /home/ctang/kvm/bin/qemu-system-x86_64(cpu_outb+0x27) [0x812b4e6] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x808d267] > /home/ctang/kvm/bin/qemu-system-x86_64(kvm_run+0x2f4) [0x808f4b8] > /home/ctang/kvm/bin/qemu-system-x86_64(kvm_cpu_exec+0x56) [0x80907b2] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x8090f4d] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x8091098] > /lib/tls/i686/cmov/libpthread.so.0 [0xb7fd24ff] > /lib/tls/i686/cmov/libc.so.6(clone+0x5e) [0xb7f0149e] > > /home/ctang/kvm/qemu-kvm-0.12.3/qemu-kvm.c : 2537 thread: b7e056d0 > /home/ctang/kvm/bin/qemu-system-x86_64(qemu_mutex_lock_iothread+0x1a) > [0x809229d] > /home/ctang/kvm/bin/qemu-system-x86_64(main_loop_wait+0x25c) [0x806ee2a] > /home/ctang/kvm/bin/qemu-system-x86_64(kvm_main_loop+0x1ff) [0x80916a1] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x806f5c2] > /home/ctang/kvm/bin/qemu-system-x86_64(main+0x2e2c) [0x80736d1] > /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe5) [0xb7e33775] > /home/ctang/kvm/bin/qemu-system-x86_64 [0x8068bb1] kvm_cpu_exec() never calls qemu_mutex_lock_iothread() but it does lock the underlying mutex via post_kvm_run(). It's just confusing because vl.c calls it the "iothread mutex" whereas qemu-kvm.c calls it "qemu mutex" and there are wrapper functions. Does this help? Stefan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
