kern/136945: [ufs] [lor] filedesc structure/ufs (poll)

[John Baldwin]

On Wednesday 29 July 2009 11:20:21 am Rene Ladan wrote:
> 2009/7/29 John Baldwin <jhb at freebsd.org>:
> > On Wednesday 29 July 2009 5:52:24 am Rene Ladan wrote:
> >> 2009/7/28 John Baldwin <jhb at freebsd.org>:
> >> > On Tuesday 28 July 2009 10:03:40 am Rene Ladan wrote:
> >> >> 2009/7/28 John Baldwin <jhb at freebsd.org>:
> >> >> > On Monday 27 July 2009 10:00:05 am Rene Ladan wrote:
> >> >> >> The following reply was made to PR kern/136945; it has been noted 
by
> >> > GNATS.
> >> >> >>
> >> >> >> From: Rene Ladan <rene at freebsd.org>
> >> >> >> To: John Baldwin <jhb at freebsd.org>
> >> >> >> Cc: bug-followup at freebsd.org
> >> >> >> Subject: Re: kern/136945: [ufs] [lor] filedesc structure/ufs (poll)
> >> >> >> Date: Mon, 27 Jul 2009 15:51:15 +0200
> >> >> >>
> >> >> >>  2009/7/27 John Baldwin <jhb at freebsd.org>:
> >> >> >>  > I would actually expect this to be the correct order for these 
two
> >> >> > locks.=
> >> >> >>   =A0Can
> >> >> >>  > you capture the output of the 'debug.witness.fullgraph' sysctl 
to a
> >> > file?
> >> >> >>  >
> >> >> >>  Yes, see attachment.  I'm still running the same 8.0-BETA2.
> >> >> >
> >> >> > Hmm, the attachment was eaten by a grue, can you post the file
> > somewhere?
> >> >> >
> >> >> Yes, see ftp://rene-ladan.nl/pub/freebsd/kern_136945.txt
> >> >
> >> > Ok, it looks like it did encounter a UFS -> filedesc order at some
> > point.  Can
> >> > you patch sys/kern/subr_witness.c to add a section to the order_lists[]
> > array
> >> > after the 'ZFS locking list' and before the spin locks list that looks
> > like
> >> > this:
> >> >
> >> >        { "filedesc structure", &lock_class_sx },
> >> >        { "ufs", &lock_class_lockmgr},
> >> >        { NULL, NULL },
> >> >
> >> The LOR seems to be gone, previously it showed up only once right
> >> after booting the system.
> >>
> >> But now a new LOR (according to the LOR page) seems pop up:
> >> Trying to mount root from ufs:/dev/ad0s1a
> >> lock order reversal:
> >>  1st 0xffffff0002a4ad80 ufs (ufs) 
@ /usr/src/sys/ufs/ffs/ffs_vfsops.c:1465
> >>  2nd 0xffffff0002b29a48 filedesc structure (filedesc structure) @
> >> /usr/src/sys/kern/kern_descrip.c:2478
> >> KDB: stack backtrace:
> >> db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
> >> _witness_debugger() at _witness_debugger+0x49
> >> witness_checkorder() at witness_checkorder+0x7ea
> >> _sx_xlock() at _sx_xlock+0x44
> >> mountcheckdirs() at mountcheckdirs+0x80
> >> vfs_donmount() at vfs_donmount+0xfbf
> >> kernel_mount() at kernel_mount+0xa1
> >> vfs_mountroot_try() at vfs_mountroot_try+0x177
> >> vfs_mountroot() at vfs_mountroot+0x47d
> >> start_init() at start_init+0x62
> >> fork_exit() at fork_exit+0x12a
> >> fork_trampoline() at fork_trampoline+0xe
> >> --- trap 0, rip = 0, rsp = 0xffffff800001ad30, rbp = 0 ---
> >>
> >> The output of `df' and `mount' looks ok.
> >
> > Yes, this is the "real" LOR as "filedesc" -> "ufs" in the poll() case 
should
> > be the normal order.  I believe this should fix it.  mountcheckdirs() 
doesn't
> > need the vnodes locked, it just needs the caller to hold references on 
them
> > so they aren't recycled:
> >
> > --- //depot/projects/smpng/sys/kern/vfs_mount.c#96
> > +++ /home/jhb/work/p4/smpng/sys/kern/vfs_mount.c
> > @@ -1069,9 +1069,10 @@
> >                vfs_event_signal(NULL, VQ_MOUNT, 0);
> >                if (VFS_ROOT(mp, LK_EXCLUSIVE, &newdp))
> >                        panic("mount: lost mount");
> > +               VOP_UNLOCK(newdp, 0);
> > +               VOP_UNLOCK(vp, 0);
> >                mountcheckdirs(vp, newdp);
> > -               vput(newdp);
> > -               VOP_UNLOCK(vp, 0);
> > +               vrele(newdp);
> >                if ((mp->mnt_flag & MNT_RDONLY) == 0)
> >                        error = vfs_allocate_syncvnode(mp);
> >                vfs_unbusy(mp);
> >
> The LOR is still present, but at a different place without the
> mountcheckdirs() call (not on the LOR page either) :

Ok, try this patch as well:

--- //depot/projects/smpng/sys/kern/vfs_mount.c#97
+++ /home/jhb/work/p4/smpng/sys/kern/vfs_mount.c
@@ -1481,6 +1481,8 @@
 	if (VFS_ROOT(TAILQ_FIRST(&mountlist), LK_EXCLUSIVE, &rootvnode))
 		panic("Cannot find root vnode");
 
+	VOP_UNLOCK(rootvnode, 0);
+
 	p = curthread->td_proc;
 	FILEDESC_XLOCK(p->p_fd);
 
@@ -1496,8 +1498,6 @@
 
 	FILEDESC_XUNLOCK(p->p_fd);
 
-	VOP_UNLOCK(rootvnode, 0);
-
 	EVENTHANDLER_INVOKE(mountroot);
 }
 

-- 
John Baldwin