On Sat, Apr 9, 2011 at 4:04 PM, Sergei Trofimovich <sly...@gmail.com> wrote: > I've decided to use UML when caught some hard to > debug OOpses on btrfs. > > The first attempt to use btrfs on UML gave me stable > UML crash. I suspect it's a UML's problem. > > So I have some questions here (I'm on x86_64, > 2.6.39-rc2): > > 1. (major one) BUG_ON trace in UML does not look > as in real kernel. ud2 handler does not show us nice > backtrace, but calls some suspicious handler. > > /mnt/btr # touch asd-`seq 1 10000` > [ 95.540000] Kernel panic - not syncing: Kernel mode signal 4 > [ 95.540000] Call Trace: > [ 95.540000] 602d9908: [<60227a48>] panic+0xea/0x1e0 > [ 95.540000] 602d99b8: [<600342ed>] do_softirq+0x4d/0x70 > [ 95.540000] 602d9a08: [<60016947>] relay_signal+0x87/0xa0 > [ 95.540000] 602d9a18: [<60021f70>] set_signals+0x30/0x40 > [ 95.540000] 602d9a38: [<60021df9>] sig_handler_common+0x59/0xd0 > [ 95.540000] 602d9a58: [<60021f2c>] real_alarm_handler+0x3c/0x50 > [ 95.540000] 602d9ae0: [<6018c0a0>] strncpy+0x20/0x30 > [ 95.540000] 602d9b78: [<6002200f>] sig_handler+0x3f/0x50 > [ 95.540000] 602d9b98: [<600222a1>] handle_signal+0x71/0xb0 > [ 95.540000] 602d9be8: [<60023630>] hard_handler+0x10/0x20 > [ 95.540000] 602d9ca8: [<6011263c>] > lookup_inline_extent_backref+0x2dc/0x3f0 > [ 95.540000] > [ 95.540000] > [ 95.540000] Pid: 1, comm: sh Not tainted 2.6.39-rc2+ > > Here we have BUG_ON in lookup_inline_extent_backref+0x2dc/0x3f0, but that > pesky > hard_handler. Is it an UML bug or known and expected behaviour?
It's expected behavior. > Now I use 'gdb -p $pid' to get nicer backtrace: > > Program received signal SIGILL, Illegal instruction. > lookup_inline_extent_backref (trans=0x70c6e000, root=<value optimized out>, > path=0x70c82000, > ref_ret=<value optimized out>, bytenr=<value optimized out>, > num_bytes=<value optimized out>, parent=0, > root_objectid=5, owner=0, offset=0, insert=0) at > /home/slyfox/linux-2.6/fs/btrfs/extent-tree.c:1399 > 1399 BUG_ON(ret); > > Can UML call the same ud2 handler as the real handler? We would see > something like: It's on my maybe-TODO list. :-) > > [ 155.038388] kernel BUG at /mnt/archive/src/linux-2.6/fs/btrfs/inode.c:2967! > [ 155.038643] invalid opcode: 0000 [#1] PREEMPT SMP > > How does UML implement running userspace processes and kernel threads in it? > I guess it's a problem, why UML can't distinct where ud2 comes from and call > proper handler. UML can distinct the source of ud2. Otherwise any process within UML could kill the kernel. > 2. btrfs in UML does not work for me at all. It corrupts data right off > the start. I only need to format the filesystem, touch there ~20 > files and I get corrupted FS: > > I run the following tiny script in UML: > > /tools/mkfs.btrfs /dev/ubda > mount /mnt/btr/ > cd /mnt/btr/ > touch `seq 1 11` > ls > > The result is: > / # ./kill_btr > > WARNING! - Btrfs v0.19-35-g1b444cd-dirty IS EXPERIMENTAL > WARNING! - see http://btrfs.wiki.kernel.org before using > > fs created label (null) on /dev/ubda > nodesize 4096 leafsize 4096 sectorsize 4096 size 1.91GB > Btrfs v0.19-35-g1b444cd-dirty > [ 2.770000] device fsid f2407093ae1f3a78-9e203194e541bfbd devid 1 transid > 7 /dev/ubda > [ 2.770000] btrfS: invalid dir item name len: 12594 > [ 2.770000] btrfS: invalid dir item name len: 0 > [ 2.770000] btrfS: invalid dir item name len: 0 > 11 > > Corruption. Only last file is seen. Later, after unmount I get an OOps. > > It does not happen in real OS. I've enabled all the corruption > detecting tehniques in the kernel config and it didn't change picture. > I can share .config if you like. kernel builds only 4 minutes on my slow > laptop. > > Is there serious problems in UML block device handling? I hope not! We have had some problems with the block layer in ~2.6.32 to 2.6.35. Commit 4752690 fixed the issues. Can you please re-test it with 2.6.38? Does you script work with other file systems? > I run UML this way: > ./vmlinux \ > ubd0=$(pwd)/btr.img \ > root=/dev/root \ > rootflags="$(pwd)/root" rw rootfstype=hostfs \ > mem=256M init=/init \ > > btr.img is a 2048000000 bytes sized file. rootfs contains statically linked > busybox and latest statically linked btrfs-progs. I can share my root if > you are interested. It's tiny (btrfs-progs tree is mounted from hostfs): > $ find root/ -type f > root/bin/busybox > root/bin/strace > root/kill_btr > root/etc/fstab > root/init > > Thank you! > > -- > > Sergei > > ------------------------------------------------------------------------------ > Xperia(TM) PLAY > It's a major breakthrough. An authentic gaming > smartphone on the nation's most reliable network. > And it wants your games. > http://p.sf.net/sfu/verizon-sfdev > _______________________________________________ > User-mode-linux-devel mailing list > User-mode-linux-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel > > -- Thanks, //richard ------------------------------------------------------------------------------ Xperia(TM) PLAY It's a major breakthrough. An authentic gaming smartphone on the nation's most reliable network. And it wants your games. http://p.sf.net/sfu/verizon-sfdev _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
