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

[Rene Ladan]

2009/7/29 John Baldwin <jhb at freebsd.org>:
> 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);
>  }
>

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

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 = 0x800729dac, rsp =
0x7fffffffec88, rbp = 0x7fffffffef66 ---

René