Hi, I'm looking at a KASSERT which is triggering quite rarely for me (in terms of iterations):
panic: kernel diagnostic assertion "dt->dt_ff[i]->ff_refcnt == 0" failed: file "/usr/allsrc/src/sys/rump/librump/rumpkern/../../../kern/kern_descrip.c", line 856 Upon closer examination, it seems that this can trigger while another thread is in fd_getfile() between upping the refcount, testing for ff_file, and fd_putfile(). Removing the KASSERT seems to restore correct operation, but I didn't read the code far enough to see where the race is actually handled and what stops the code from using the wrong file. How-to-repeat: Run tests/fs/puffs/t_fuzz mountfuzz7 in a loop. A multiprocessor kernel might produce a more reliable result, so set RUMP_NCPU unless you have a multiprocessor host. Depending on timings and how the get/put thread runs, you might even see the refcount as 0 in the core. Does anyone see something wrong with the analysis? If not, I'll create a dedidated test and file a PR.
