Peter Xu <pet...@redhat.com> wrote: > In qemu_file_shutdown(), there's a possible race if with current order of > operation. There're two major things to do: > > (1) Do real shutdown() (e.g. shutdown() syscall on socket) > (2) Update qemufile's last_error > > We must do (2) before (1) otherwise there can be a race condition like: > > page receiver other thread > ------------- ------------ > qemu_get_buffer() > do shutdown() > returns 0 (buffer all zero) > (meanwhile we didn't check this retcode) > try to detect IO error > last_error==NULL, IO okay > install ALL-ZERO page > set last_error > --> guest crash! > > To fix this, we can also check retval of qemu_get_buffer(), but not all > APIs can be properly checked and ultimately we still need to go back to > qemu_file_get_error(). E.g. qemu_get_byte() doesn't return error. > > Maybe some day a rework of qemufile API is really needed, but for now keep > using qemu_file_get_error() and fix it by not allowing that race condition > to happen. Here shutdown() is indeed special because the last_error was > emulated. For real -EIO errors it'll always be set when e.g. sendmsg() > error triggers so we won't miss those ones, only shutdown() is a bit tricky > here. > > Cc: Daniel P. Berrange <berra...@redhat.com> > Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > Signed-off-by: Peter Xu <pet...@redhat.com>
Reviewed-by: Juan Quintela <quint...@redhat.com>
