Date: Thu, 11 Dec 2008 14:53:49 -0800 From: David Wolfskill <david@catwhisker.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: hackers@freebsd.org, current@freebsd.org Subject: Re: NFS (& amd?) dysfunction descending a hierarchy Message-ID: <20081211225349.GB5597@albert.catwhisker.org> In-Reply-To: <20081210170620.GS2038@deviant.kiev.zoral.com.ua> References: <20081203001538.GC96383@bunrab.catwhisker.org> <20081209190110.GW60731@albert.catwhisker.org> <Pine.GSO.4.63.0812101124430.24743@muncher.cs.uoguelph.ca> <20081210165022.GJ60731@albert.catwhisker.org> <20081210170620.GS2038@deviant.kiev.zoral.com.ua>
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On Wed, Dec 10, 2008 at 07:06:20PM +0200, Kostik Belousov wrote:
> ...
> > What concerns me is that even if the attempted unmount gets EBUSY, the
> > user-level process descending the directory hierarchy is getting ENOENT
> > trying to issue fstatfs() against an open file descriptor.
> >=20
> > I'm having trouble figuring out any way that makes any sense.
>=20
> Basically, the problem is that NFS uses shared lookup, and this allows
> for the bug where several negative namecache entries are created for
> non-existent node. Then this node gets created, removing only the first
> negative namecache entry. For some reasons, vnode is reclaimed; amd'
> tasting of unmount is a good reason for vnode to be reclaimed.
>=20
> Now, you have existing path and a negative cache entry. This was
> reported by Peter Holm first, I listed relevant revisions that
> should fix this in previous mail.
Well, I messed up the machine I had been using for testing, and needed
to wait for IT to do something to it since I don't have physical or
console access to it.
So after I happened to demonstrate the effect using my desktop -- which
had been running RELENG_7_1, sources updated as of around 0400 hrs.
US/Pacific -- I decided to go ahead and update the desktop to RELENG_7_1
as of this morning (which had the commit to sys/kern/vfs_cache.c), then
test.
It still failed, apparently in the same way; details below.
First, here's a list of the files that were changed:
U lib/libarchive/archive_read_support_format_iso9660.c
U lib/libarchive/archive_string.c
U lib/libarchive/archive_string.h
U lib/libc/gen/times.3
U lib/libc/i386/sys/pipe.S
U lib/libc/i386/sys/reboot.S
U lib/libc/i386/sys/setlogin.S
U lib/libutil/Makefile
U lib/libutil/kinfo_getfile.c
U lib/libutil/kinfo_getvmmap.c
U lib/libutil/libutil.h
U share/man/man4/bce.4
U share/man/man5/Makefile
U share/man/man5/fstab.5
U share/man/man5/nullfs.5
U sys/amd64/Makefile
U sys/boot/forth/loader.conf.5
U sys/dev/ale/if_ale.c
U sys/dev/bce/if_bce.c
U sys/dev/cxgb/cxgb_main.c
U sys/dev/cxgb/common/cxgb_ael1002.c
U sys/dev/cxgb/common/cxgb_t3_hw.c
U sys/dev/cxgb/common/cxgb_xgmac.c
U sys/dev/re/if_re.c
U sys/fs/nullfs/null_vnops.c
U sys/kern/Make.tags.inc
U sys/kern/kern_descrip.c
U sys/kern/kern_proc.c
U sys/kern/vfs_cache.c
U sys/netinet/in_pcb.h
U sys/pci/if_rlreg.h
U sys/sys/sysctl.h
U sys/sys/user.h
U sys/ufs/ufs/ufs_quota.c
U usr.bin/procstat/Makefile
U usr.bin/procstat/procstat_files.c
U usr.bin/procstat/procstat_vm.c
U usr.bin/tar/util.c
U usr.bin/tar/test/Makefile
U usr.bin/tar/test/test_strip_components.c
U usr.bin/tar/test/test_symlink_dir.c
U usr.bin/xargs/xargs.1
U usr.sbin/mtree/mtree.c
We see that sys/kern/vfs_cache.c is, indeed, among them. And:
dwolf-bsd(7.1-P)[5] grep '\$FreeBSD' /sys/kern/vfs_cache.c
__FBSDID("$FreeBSD: src/sys/kern/vfs_cache.c,v 1.114.2.3 2008/12/09 16:20:5=
8 kib Exp $");
dwolf-bsd(7.1-P)[6]=20
That should correspond to the desired version of the file.
Here we see an excerpt from the ktrace output for the amd(8) process and
its children; this is a point when amd(8) is trying an unmount() to see
if it can get away with it:
977 amd 1229033597.269612 CALL gettimeofday(0x807ad48,0)
977 amd 1229033597.269620 RET gettimeofday 0
977 amd 1229033597.269630 CALL sigprocmask(SIG_BLOCK,0xbfbfeaec,0x=
bfbfeadc)
977 amd 1229033597.269637 RET sigprocmask 0
977 amd 1229033597.269645 CALL fork
977 amd 1229033597.273810 RET fork 1712/0x6b0
1712 amd 1229033597.273811 RET fork 0
977 amd 1229033597.273836 CALL sigprocmask(SIG_SETMASK,0xbfbfeadc,=
0)
1712 amd 1229033597.273845 CALL getpid
977 amd 1229033597.273850 RET sigprocmask 0
1712 amd 1229033597.273855 RET getpid 1712/0x6b0
977 amd 1229033597.273864 CALL gettimeofday(0x807ad48,0)
977 amd 1229033597.273874 RET gettimeofday 0
1712 amd 1229033597.273878 CALL unmount(0x2832c610,<invalid>0)
=2E..
1712 amd 1229033597.352643 RET unmount -1 errno 16 Device busy
1712 amd 1229033597.352695 CALL sigprocmask(SIG_BLOCK,0x28097c00,0x=
bfbfea0c)
1712 amd 1229033597.352728 RET sigprocmask 0
1712 amd 1229033597.352751 CALL sigprocmask(SIG_SETMASK,0x28097c10,=
0)
1712 amd 1229033597.352769 RET sigprocmask 0
1712 amd 1229033597.352781 CALL sigprocmask(SIG_BLOCK,0x28097c00,0x=
bfbfe9dc)
1712 amd 1229033597.352790 RET sigprocmask 0
1712 amd 1229033597.352801 CALL sigprocmask(SIG_SETMASK,0x28097c10,=
0)
1712 amd 1229033597.352805 RET sigprocmask 0
1712 amd 1229033597.352815 CALL exit(0x10)
977 amd 1229033597.353085 RET select -1 errno 4 Interrupted syste=
m call
977 amd 1229033597.353093 PSIG SIGCHLD caught handler=3D0x805de50 =
mask=3D0x0 code=3D0x0
977 amd 1229033597.353103 CALL wait4(0xffffffff,0xbfbfe83c,WNOHANG=
,0)
977 amd 1229033597.353116 RET wait4 1712/0x6b0
977 amd 1229033597.353122 CALL wait4(0xffffffff,0xbfbfe83c,WNOHANG=
,0)
977 amd 1229033597.353127 RET wait4 -1 errno 10 No child processes
So amd(8) master process (pid 977) jorks off a child (pid 1712) to
try an umount(), which it initiates at 1229033597.273878. At
1229033597.352643 the child gets control back, as well as an EBUSY,
which I would expect to mean that the attempt failed. The child
exits at 1229033597.352815 with a status code of 16.
Armed with that, we look at a ktrace excerpt from "rm -fr":
1660 rm 1229033597.283277 CALL rmdir(0x2822b388)
1660 rm 1229033597.283283 NAMI "stvef-paks"
1660 rm 1229033597.285599 RET rmdir 0
1660 rm 1229033597.285620 CALL stat(0x2822b3e8,0xbfbfe8dc)
1660 rm 1229033597.285626 NAMI "stvef-server"
1660 rm 1229033597.286071 STRU struct stat {dev=3D83951372, ino=3D=
20124614, mode=3Ddrwxr-xr-x , nlink=3D3, uid=3D9874, gid=3D929, rdev=3D0, a=
time=3D1228844788, stime=3D1227555769, ctime=3D1228845828.326650000, birtht=
ime=3D0, size=3D4096, blksize=3D4096, blocks=3D8, flags=3D0x0 }
1660 rm 1229033597.286078 RET stat 0
1660 rm 1229033597.286084 CALL open(0x2822b3e8,O_NONBLOCK,<unused>=
0x1)
1660 rm 1229033597.286091 NAMI "stvef-server"
1660 rm 1229033597.287145 RET open 4
1660 rm 1229033597.287154 CALL fstat(0x4,0xbfbfe8dc)
1660 rm 1229033597.287161 STRU struct stat {dev=3D83951372, ino=3D=
20124614, mode=3Ddrwxr-xr-x , nlink=3D3, uid=3D9874, gid=3D929, rdev=3D0, a=
time=3D1228844788, stime=3D1227555769, ctime=3D1228845828.326650000, birtht=
ime=3D0, size=3D4096, blksize=3D4096, blocks=3D8, flags=3D0x0 }
1660 rm 1229033597.287166 RET fstat 0
1660 rm 1229033597.287171 CALL fcntl(0x4,F_SETFD,FD_CLOEXEC)
1660 rm 1229033597.287177 RET fcntl 0
1660 rm 1229033597.287187 CALL fstatfs(0x4,0xbfbfe704)
1660 rm 1229033597.287195 RET fstatfs -1 errno 2 No such file or =
directory
1660 rm 1229033597.287202 CALL close(0x4)
1660 rm 1229033597.287211 RET close 0
[Sorry for the long lines....]
Here we see that the "rm" process (pid 1660) removed a directory
named stvef-paks sucessfully in the interval between 1229033597.283277
(when the request was made) and 1229033597.285599 (when the 0 return
occurred). The "rm" process proceeds to process a directory named
stvef-server:
* At 1229033597.285620 it issues a stat(); the successful return
is at 1229033597.286078.
* At 1229033597.286084 it issues an open(); the successful return
is at 1229033597.287145. The FD is 4.
* At 1229033597.287154 it issues an fstat() against FD 4; the successful
return is at 1229033597.287166.
* At 1229033597.287171 it issues an fcntl() against FD 4; the
successful return is at 1229033597.287177.
* At 1229033597.287187 it issues an fstatfs() against FD 4; the
unsuccessful return is at 1229033597.287195, claiming ENOENT.
Say WHAT??!?
I expect to be able to test a bit more promptly now.
Peace,
david
--=20
David H. Wolfskill david@catwhisker.org
Depriving a girl or boy of an opportunity for education is evil.
See http://www.catwhisker.org/~david/publickey.gpg for my public key.
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