Eric Blake <ebl...@redhat.com> writes: > On Tue, May 23, 2023 at 06:39:03PM -0300, Fabiano Rosas wrote: >> From: João Silva <jsi...@suse.de> >> >> The fstat call can take a long time to finish when running over >> NFS. Add a version of it that runs in the thread pool. >> >> Adapt one of its users, raw_co_get_allocated_file size to use the new >> version. That function is called via QMP under the qemu_global_mutex >> so it has a large chance of blocking VCPU threads in case it takes too >> long to finish. >> >> Signed-off-by: João Silva <jsi...@suse.de> >> Signed-off-by: Fabiano Rosas <faro...@suse.de> >> --- >> block/file-posix.c | 40 +++++++++++++++++++++++++++++++++++++--- >> include/block/raw-aio.h | 4 +++- >> 2 files changed, 40 insertions(+), 4 deletions(-) > > Should this change occur earlier in the series, before calling > commands are marked with QAPI coroutine flags? Otherwise, you have a > bisection bug, where something marked coroutine can end up hanging > when it calls a blocking syscall in the wrong context without the help > of this patch offloading the syscall into a helper thread.
Hmm, I'm not sure. To submit the work to the thread pool we need to be in a coroutine already. If the syscall blocks for too long we'd be trading blocking the coroutine vs. blocking a vcpu thread anyway. I have tested each patch to avoid bisection issues, but maybe it would be warranted to merge both parts into a single patch. Or arrange them in some other way... I'll experiment with it.
