#42 — Daemon crashes on concurrent activity

The daemon crashes when userland actions are triggered in rapid succession.

$ zfs list -rHoname lin_recv | xargs -trn1 zfs set snapdir=hidden
[output ok]

$ zfs list -rHoname lin_recv | xargs -P8 -trn1 zfs set snapdir=hidden
[immediate crash of daemon]

When running under gdb 'bad address' and 'SIGPIPE' are witnessed. I recognize that from badly shielded cur_fd. This should not happen. Next step:

$ for a in $(zfs list -rHoname lin_recv); do sleep .05; zfs set snapdir=hidden "$a"& done; wait

Works like a charm. The tiny sleep allows for proper isolation of the threads. This suggests to me that thread initialization is at fault. I have found the offending line:
cmdlistener.c:118 uses a static. This static is illegally shared with other threads initializing at the same time.

I attach the patch that removes the race condition/isolation violation window. This has been pushed to testing as 0dc59d7a5cc20e1e0c1658ce07b6b84dd0d51460