<div dir="ltr">If I remember correctly, udev (recent versions) takes a BSD lock using flock(2) while processing the device, and tools are supposed to do the same. The flock() call can be set to wait until the lock can be taken. </div> <div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Nov 26, 2023 at 1:40 AM Richard Weinberger <<a href="mailto:richard.weinberger@gmail.com">richard.weinberger@gmail.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hello! After upgrading my main test worker to a recent distribution, the UBI test suite [0] fails at various places with -EBUSY. The reason is that these tests create and remove UBI volumes rapidly. A typical test sequence is as follows: 1. creation of /dev/ubi0_0 2. some exclusive operation, such as atomic update or volume resize on /dev/ubi0_0 3. removal of /dev/ubi0_0 Both steps 2 and 3 can fail with -EBUSY because the udev worker still holds a file descriptor to /dev/ubi0_0. FWIW, the problem can also get triggered using UBI's shell utilities if the system is fast enough, e.g. # ubimkvol -N testv -S 50 -n 0 /dev/ubi0 && ubirmvol -n 0 /dev/ubi0 Volume ID 0, size 50 LEBs (793600 bytes, 775.0 KiB), LEB size 15872 bytes (15.5 KiB), dynamic, name "testv", alignment 1 ubirmvol: error!: cannot UBI remove volume error 16 (Device or resource busy) Instead of adding a retry loop around -EBUSY, I believe the best solution is to add code to wait for udev. For example, having a udev barrier in ubi_mkvol() and ubi_rmvol() [1] seems like a good idea to me. What function from libsystemd do you suggest for waiting until udev is done with rule processing? My naive approach, using udev_queue_is_empty() and sd_device_get_is_initialized(), does not resolve all failures so far. Firstly, udev_queue_is_empty() doesn't seem to be exported by libsystemd. I have open-coded it as: static int udev_queue_is_empty(void) { return access("/run/udev/queue", F_OK) < 0 ? (errno == ENOENT ? true : -errno) : false; } Additionally, sd_device_get_is_initialized() seems to return sometimes true even if the udev worker still has the volume open. In short, which API do you recommend to ensure that the device my thread has created is actually usable? [0]: <a href="http://git.infradead.org/mtd-utils.git/tree/HEAD:/tests/ubi-tests" rel="noreferrer" target="_blank">http://git.infradead.org/mtd-utils.git/tree/HEAD:/tests/ubi-tests</a> [1]: <a href="http://git.infradead.org/mtd-utils.git/blob/HEAD:/lib/libubi.c#l994" rel="noreferrer" target="_blank">http://git.infradead.org/mtd-utils.git/blob/HEAD:/lib/libubi.c#l994</a> -- Thanks, //richard </blockquote></div> -- <div dir="ltr" class="gmail_signature"><div dir="ltr">Mantas Mikulėnas</div></div>