On Sat, Aug 23, 2025 at 10:55 AM Ming Lei <ming.lei@xxxxxxxxxx> wrote: > > When running test_stress_04.sh, the following warning is triggered: > > WARNING: CPU: 1 PID: 135 at drivers/block/ublk_drv.c:1933 ublk_ch_release+0x423/0x4b0 [ublk_drv] > > This happens when the daemon is abruptly killed: > > - some references may still be held, because registering IO buffer > doesn't grab ublk char device reference > > OR > > - io->task_registered_buffers won't be cleared because io buffer is > released from non-daemon context > > For zero-copy and auto buffer register modes, I/O reference crosses > syscalls, so IO reference may not be dropped naturally when ublk server is > killed abruptly. However, when releasing io_uring context, it is guaranteed > that the reference is dropped finally, see io_sqe_buffers_unregister() from > io_ring_ctx_free(). > > Fix this by adding ublk_drain_io_references() that: > - Waits for active I/O references dropped > - Reinitializes io->ref and io->task_registered_buffers to clean state > > This way won't hang because releasing ublk char device doesn't depend on > unregistering sqe buffers in do_exit(). Actually io_uring file close may rely on ublk char dev close, so still has hang risk, will send V2 for addressing it. Thanks,
