Re: [Libguestfs] [libnbd PATCH] tests: Enhance errors test

On Thu, Jun 27, 2019 at 10:18:30PM -0500, Eric Blake wrote: > + /* Queue up a write command so large that we block on POLLIN, then queue > + * multiple disconnects. XXX The last one should fail. > + */ > + if (nbd_aio_pwrite (nbd, buf, 2 * 1024 * 1024, 0, 0) == -1) { > + fprintf (stderr, "%s: %s\n", argv[0], nbd_get_error ()); > + exit (EXIT_FAILURE); > + } > + if ((nbd_aio_get_direction (nbd) & LIBNBD_AIO_DIRECTION_WRITE) == 0) { > + fprintf (stderr, "%s: test failed: " > + "expect to be blocked on write\n", > + argv[0]); > + exit (EXIT_FAILURE); > + } This test fails when run under valgrind. An abbreviated log shows what's happening: libnbd: debug: nbd_aio_pwrite: event CmdIssue: READY -> ISSUE_COMMAND.START libnbd: debug: nbd_aio_pwrite: transition: ISSUE_COMMAND.START -> ISSUE_COMMAND. SEND_REQUEST libnbd: debug: nbd_aio_pwrite: transition: ISSUE_COMMAND.SEND_REQUEST -> ISSUE_C OMMAND.PREPARE_WRITE_PAYLOAD libnbd: debug: nbd_aio_pwrite: transition: ISSUE_COMMAND.PREPARE_WRITE_PAYLOAD - > ISSUE_COMMAND.SEND_WRITE_PAYLOAD libnbd: debug: nbd_aio_pwrite: transition: ISSUE_COMMAND.SEND_WRITE_PAYLOAD -> I SSUE_COMMAND.FINISH libnbd: debug: nbd_aio_pwrite: transition: ISSUE_COMMAND.FINISH -> READY /home/rjones/d/libnbd/tests/.libs/lt-errors: test failed: expect to be blocked on write It seems as if this is caused by valgrinded code running more slowly, rather than an actual valgrind/memory error.

I wonder if we could remove the race using a custom nbdkit-sh-plugin which would block on writes until (eg) a local trigger file was touched? Even that seems as if it would depend on the amount of data that the kernel is able to buffer.