Bug #3325
nsmb_close locking and teardown deadlock
0%
Description
One may observe the SMB server failing to authenticate domain users,
and upon examining stacks, one may find:
> ffffff2da452b560$<threadlist
ADDR PROC LWP CLS PRI WCHAN
ffffff2da452b560 ffffff2a6d324730 ffffff2aa3480e20 1 59 ffffff303ceb1dc4
PC: _resume_from_idle+0xf1 CMD: /usr/lib/smbsrv/smbd start
stack pointer for thread ffffff2da452b560: ffffff013557ea70
[ ffffff013557ea70 _resume_from_idle+0xf1() ]
swtch+0x145()
cv_wait_sig+0x14d()
smb_iod_reconnect+0x59()
smb_usr_get_ssn+0x114()
nsmb_ioctl+0x125()
cdev_ioctl+0x45()
spec_ioctl+0x5a()
fop_ioctl+0x7b()
ioctl+0x18e()
dtrace_systrace_syscall32+0x11a()
_sys_sysenter_post_swapgs+0x149()
Attempts (by root) to connect to the current AD server will also hang.
Updated by Gordon Ross about 8 years ago
The smbiod is in the middle of shutting down it's connection to the AD server, typically due to it being idle. During the nsmb_close() call, it holds the &dev_lck mutex while calling nsmb_close2(). That in turn creates a close request which mistakenly tries to initiate a reconnect to this server. The reconnect can not proceed because it needs to reenter the driver and take the lock that we already hold. Deadlock.
We're doing two things, either of which alone would fix this deadlock, both of which are improvements on their own:
(a) don't hold dev_lck during nsmb_close2
(b) don't trigger a reconnect for close or "tdis".
Part (b) is OK because the SMB protocol assures us that, once a connect is closed, all file IDs, tree IDs, etc are destroyed by the server. It never makes sense to reconnect just to do that.
Updated by Gordon Ross about 8 years ago
- Status changed from New to Resolved
From 39f633a09e54fab2b9cf8d9d3ddc2a043b3e7465 Mon Sep 17 00:00:00 2001 From: Bayard Bell <bayard.bell@nexenta.com> Date: Wed, 30 Jan 2013 23:35:38 +0100 Subject: [PATCH] 3325 nsmb_close locking and teardown deadlock Reviewed by: Albert Lee <trisk@nexenta.com> Reviewed by: Gordon Ross <gwr@nexenta.com> Reviewed by: Yakov Zaytsev <yakov@nexenta.com> Approved by: Richard Lowe <richlowe@richlowe.net>