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Date:      Thu, 30 Jul 2009 11:05:32 +0200
From:      Rene Ladan <rene@freebsd.org>
To:        John Baldwin <jhb@freebsd.org>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: kern/136945: [ufs] [lor] filedesc structure/ufs (poll)
Message-ID:  <e890cae60907300205v5d3d5586qe86969bd28fe8621@mail.gmail.com>
In-Reply-To: <200907291135.17569.jhb@freebsd.org>
References:  <200907271400.n6RE05Rv056472@freefall.freebsd.org> <200907290742.20838.jhb@freebsd.org> <e890cae60907290820i65abae2fracbc5ab935465089@mail.gmail.com> <200907291135.17569.jhb@freebsd.org>

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2009/7/29 John Baldwin <jhb@freebsd.org>:
> On Wednesday 29 July 2009 11:20:21 am Rene Ladan wrote:
>> 2009/7/29 John Baldwin <jhb@freebsd.org>:
>> > On Wednesday 29 July 2009 5:52:24 am Rene Ladan wrote:
>> >> 2009/7/28 John Baldwin <jhb@freebsd.org>:
>> >> > On Tuesday 28 July 2009 10:03:40 am Rene Ladan wrote:
>> >> >> 2009/7/28 John Baldwin <jhb@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 not=
ed
> by
>> >> > GNATS.
>> >> >> >>
>> >> >> >> From: Rene Ladan <rene@freebsd.org>
>> >> >> >> To: John Baldwin <jhb@freebsd.org>
>> >> >> >> Cc: bug-followup@freebsd.org
>> >> >> >> Subject: Re: kern/136945: [ufs] [lor] filedesc structure/ufs (p=
oll)
>> >> >> >> Date: Mon, 27 Jul 2009 15:51:15 +0200
>> >> >> >>
>> >> >> >> =A02009/7/27 John Baldwin <jhb@freebsd.org>:
>> >> >> >> =A0> I would actually expect this to be the correct order for t=
hese
> two
>> >> >> > locks.=3D
>> >> >> >> =A0 =3DA0Can
>> >> >> >> =A0> you capture the output of the 'debug.witness.fullgraph' sy=
sctl
> to a
>> >> > file?
>> >> >> >> =A0>
>> >> >> >> =A0Yes, see attachment. =A0I'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. =A0Can
>> >> > you patch sys/kern/subr_witness.c to add a section to the order_lis=
ts[]
>> > array
>> >> > after the 'ZFS locking list' and before the spin locks list that lo=
oks
>> > like
>> >> > this:
>> >> >
>> >> > =A0 =A0 =A0 =A0{ "filedesc structure", &lock_class_sx },
>> >> > =A0 =A0 =A0 =A0{ "ufs", &lock_class_lockmgr},
>> >> > =A0 =A0 =A0 =A0{ 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:
>> >> =A01st 0xffffff0002a4ad80 ufs (ufs)
> @ /usr/src/sys/ufs/ffs/ffs_vfsops.c:1465
>> >> =A02nd 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 =3D 0, rsp =3D 0xffffff800001ad30, rbp =3D 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. =A0I believe this should fix it. =A0mountcheckdir=
s()
> 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 @@
>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0vfs_event_signal(NULL, VQ_MOUNT, 0);
>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (VFS_ROOT(mp, LK_EXCLUSIVE, &newdp))
>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0panic("mount: lost moun=
t");
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 VOP_UNLOCK(newdp, 0);
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 VOP_UNLOCK(vp, 0);
>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0mountcheckdirs(vp, newdp);
>> > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 vput(newdp);
>> > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 VOP_UNLOCK(vp, 0);
>> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 vrele(newdp);
>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if ((mp->mnt_flag & MNT_RDONLY) =3D=3D =
0)
>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0error =3D vfs_allocate_=
syncvnode(mp);
>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0vfs_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 @@
> =A0 =A0 =A0 =A0if (VFS_ROOT(TAILQ_FIRST(&mountlist), LK_EXCLUSIVE, &rootv=
node))
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0panic("Cannot find root vnode");
>
> + =A0 =A0 =A0 VOP_UNLOCK(rootvnode, 0);
> +
> =A0 =A0 =A0 =A0p =3D curthread->td_proc;
> =A0 =A0 =A0 =A0FILEDESC_XLOCK(p->p_fd);
>
> @@ -1496,8 +1498,6 @@
>
> =A0 =A0 =A0 =A0FILEDESC_XUNLOCK(p->p_fd);
>
> - =A0 =A0 =A0 VOP_UNLOCK(rootvnode, 0);
> -
> =A0 =A0 =A0 =A0EVENTHANDLER_INVOKE(mountroot);
> =A0}
>

Still no luck, I now get a LOR that is similar to LOR 281 right after booti=
ng:

lock order reversal:
 1st 0xffffff0002c2c7f8 ufs (ufs) @ /usr/src/sys/kern/vfs_subr.c:2083
 2nd 0xffffff0002b2a248 filedesc structure (filedesc structure) @
/usr/src/sys/kern/vfs_syscalls.c:3776
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_slock() at _sx_slock+0x44
kern_mkdirat() at kern_mkdirat+0x201
syscall() at syscall+0x1af
Xfast_syscall() at Xfast_syscall+0xe1
--- syscall (136, FreeBSD ELF64, mkdir), rip =3D 0x800729dac, rsp =3D
0x7fffffffec88, rbp =3D 0x7fffffffef66 ---

Ren=E9



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