umount() taking minutes for FUSE filesystems

[Stefan Esser]

Am 04.09.17 um 23:14 schrieb Ben RUBSON:
> I managed to reproduce the issue.
> unmount takes exactly 60 seconds, as if a timeout was running.
> 
> # procstat -kk $!
> COMM     TDNAME KSTACK                       
> printcap -      mi_switch+0xd2 sleepq_catch_signals+0xb7 sleepq_timedwait_sig+0x10 _sleep+0x26f fdisp_wait_answ+0x171 fuse_vfsop_unmount+0xf5 dounmount+0x9b6 sys_unmount+0x41b amd64_syscall+0x4ce Xfast_syscall+0xfb 
> 
> # uname -sr
> FreeBSD 11.0-RELEASE-p9

I have given the exact position of this 60 second msleep() in multiple
mails before. It is in fuse_ipc.c, the particular msleep with "fu_ans"
(line 333 in -CURRENT).

I did not try to diagnose, why this particular umount() takes so long,
while others are fast, but it is obvious that the kernel module does
wait for a signal at the end of some IPC and the signal is either lost
or never sent. There is a check for a dead connection, just before the
msleep() and the connection is considered alive at that point (and
should be, to support the umount() result being reported).

I did not have time to look into this during the previous week and
won't during this week, but it should not be too hard to see, what's
going on. A starting point could be to compare this test with those
that perform the unmount without delay.

Regards, STefan