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    SubjectRe: Heads-up: 3.6.2 / 3.6.3 NFS server oops: 3.6.2+ regression? (also an unrelated ext4 data loss bug)
    Date
    On 23 Oct 2012, J. Bruce Fields uttered the following:
    > nfs-utils shouldn't be capable of oopsing the kernel, so from my
    > (selfish) point of view I'd actually rather you stick with whatever you
    > have and try to reproduce the oops.

    Reproduced in 3.6.3, not in 3.6.1, not tried 3.6.2. Capturing it was
    rendered somewhat difficult by an ext4/JBD2 bug which leads to data loss
    in /var on every reboot out of 3.6.1 and on some reboots out of 3.6.3 (I
    have runs of NULs in my logs now, which keep eating the oopses):

    [while in 3.6.1]
    [ 88.565698] JBD2: Spotted dirty metadata buffer (dev = dm-5, blocknr = 0). There's a risk of filesystem corruption in case of system crash.
    [ 88.799263] JBD2: Spotted dirty metadata buffer (dev = dm-5, blocknr = 0). There's a risk of filesystem corruption in case of system crash.
    [ 89.648152] ------------[ cut here ]------------
    [ 89.648386] WARNING: at fs/inode.c:280 drop_nlink+0x25/0x42()
    [ 89.648614] Hardware name: empty
    [ 89.648833] Modules linked in: firewire_ohci firewire_core [last unloaded: microcode]
    [ 89.649382] Pid: 1484, comm: dhcpd Not tainted 3.6.1-dirty #1
    [ 89.649610] Call Trace:
    [ 89.649832] [<ffffffff810608c0>] warn_slowpath_common+0x83/0x9b
    [ 89.650063] [<ffffffff810608f2>] warn_slowpath_null+0x1a/0x1c
    [ 89.650292] [<ffffffff8112efbf>] drop_nlink+0x25/0x42
    [ 89.650533] [<ffffffff81187112>] ext4_dec_count+0x26/0x28
    [ 89.650763] [<ffffffff8118abb8>] ext4_rename+0x4ec/0x7b4
    [ 89.650993] [<ffffffff81125d81>] ? vfs_rename+0xbe/0x3b7
    [ 89.651224] [<ffffffff81125f3f>] vfs_rename+0x27c/0x3b7
    [ 89.651454] [<ffffffff81127a53>] sys_renameat+0x1b1/0x228
    [ 89.651682] [<ffffffff8114bda1>] ? fsnotify+0x226/0x249
    [ 89.651911] [<ffffffff81239b75>] ? security_inode_permission+0x1e/0x20
    [ 89.652145] [<ffffffff8111a240>] ? vfs_write+0x116/0x142
    [ 89.652372] [<ffffffff81127ae5>] sys_rename+0x1b/0x1e
    [ 89.652601] [<ffffffff814fffa2>] system_call_fastpath+0x16/0x1b
    [...]
    [while having just booted into 3.6.1 after some time in 3.6.3: the FS
    was clean, and fscked on the previous boot into 3.6.3 after a previous
    instance of this bug]
    Oct 23 17:18:26 spindle crit: [ 67.625319] EXT4-fs error (device dm-5): mb_free_blocks:1300: group 65, block 2143748:freeing already freed block (bit 13828)

    This may well be a 3.6.1-specific bug fixed in 3.6.3, but it's hard to
    tell since most of my reboots are 3.6.1->3.6.3 or vice versa right now.


    Anyway, here's the NFSv4 oops (not a panic: it helps if I remember to
    turn off panic_on_oops when I come home from the holidays).

    It's a lockd problem, and probably happens during delivery of mail over
    NFS (my mailserver load soars when it happens):

    [ 813.110354] ------------[ cut here ]------------
    [ 813.110585] kernel BUG at fs/lockd/mon.c:150!
    [ 813.110878] invalid opcode: 0000 [#1] SMP
    [ 813.111173] Modules linked in: firewire_ohci firewire_core [last unloaded: microcode]
    [ 813.111727] CPU 1
    [ 813.111772] Pid: 1040, comm: lockd Not tainted 3.6.3-dirty #1 empty empty/S7010
    [ 813.112388] RIP: 0010:[<ffffffff8120fbbc>] [<ffffffff8120fbbc>] nsm_mon_unmon+0x64/0x98
    [ 813.112840] RSP: 0018:ffff88062163dcf0 EFLAGS: 00010246
    [ 813.113069] RAX: ffff88062163dcf8 RBX: 0000000000000000 RCX: 0000000000000000
    [ 813.113303] RDX: ffff88062163dd68 RSI: 0000000000000002 RDI: ffff88062163dd40
    [ 813.113537] RBP: ffff88062163dd50 R08: 0000000000000000 R09: ffffffff8120c463
    [ 813.113771] R10: ffffffff8120c463 R11: 0000000000000001 R12: 0000000000000000
    [ 813.114006] R13: ffff88061f067e40 R14: ffff88059c763a00 R15: ffff88062163de28
    [ 813.114241] FS: 0000000000000000(0000) GS:ffff88063fc40000(0000) knlGS:0000000000000000
    [ 813.114651] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    [ 813.114882] CR2: ffffffffff600400 CR3: 0000000001a0b000 CR4: 00000000000007e0
    [ 813.115116] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    [ 813.115350] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    [ 813.115584] Process lockd (pid: 1040, threadinfo ffff88062163c000, task ffff880621611640)
    [ 813.115994] Stack:
    [ 813.116210] ffff88062163dd90 ffff8805f4e044b1 00000003000186b5 ffffffff00000010
    [ 813.116761] ffff8805f4e044c1 000000000000008c 0000000000000000 ffff88062163dcf8
    [ 813.117310] ffff88062163dd68 0000000000000000 ffff8806200ce088 ffff8805f4e04400
    [ 813.117861] Call Trace:
    [ 813.118083] [<ffffffff8120fee4>] nsm_monitor+0x100/0x157
    [ 813.118315] [<ffffffff81211b4a>] nlm4svc_retrieve_args+0x62/0xd7
    [ 813.118547] [<ffffffff81211f49>] nlm4svc_proc_lock+0x3c/0xb5
    [ 813.118779] [<ffffffff8121167b>] ? nlm4svc_decode_lockargs+0x47/0xb2
    [ 813.119016] [<ffffffff814d89ca>] svc_process+0x3bf/0x6a1
    [ 813.119246] [<ffffffff8120d5f0>] lockd+0x127/0x164
    [ 813.119474] [<ffffffff8120d4c9>] ? set_grace_period+0x8a/0x8a
    [ 813.119708] [<ffffffff8107bcbc>] kthread+0x8b/0x93
    [ 813.119938] [<ffffffff815012f4>] kernel_thread_helper+0x4/0x10
    [ 813.120170] [<ffffffff8107bc31>] ? kthread_worker_fn+0xe1/0xe1
    [ 813.120401] [<ffffffff815012f0>] ? gs_change+0xb/0xb
    [ 813.120628] Code: b8 10 00 00 00 48 89 45 c0 48 8d 81 8c 00 00 00 b9 08 00 00 00 48 89 45 c8 89 d8 f3 ab 48 8d 45 a8 48 89 55 e0 48 89 45 d8 75 02 <0f> 0b 89 f6 48 c7 02 00 00 00 00 4c 89 c7 48 6b f6 38 ba 00 04
    [ 813.123627] RIP [<ffffffff8120fbbc>] nsm_mon_unmon+0x64/0x98
    [ 813.123894] RSP <ffff88062163dcf0>
    [ 813.124129] ---[ end trace 11eb11a091ffd910 ]---

    Aside: I am running with this patch, to prevent mounting of one
    NFS-mounted directory under another from failing all accesses with a
    spurious -EBUSY, a 3.6 regression -- but I can't see how this could
    cause it. I'm running with this in 3.6.1 as well:

    diff --git a/fs/dcache.c b/fs/dcache.c
    index 8086636..649a112 100644
    --- a/fs/dcache.c
    +++ b/fs/dcache.c
    @@ -2404,6 +2404,10 @@ out_unalias:
    if (likely(!d_mountpoint(alias))) {
    __d_move(alias, dentry);
    ret = alias;
    + } else {
    + printk(KERN_WARNING "VFS: __d_move()ing a d_mountpoint(), uh oh\n");
    + __d_move(alias, dentry);
    + ret = alias;
    }
    out_err:
    spin_unlock(&inode->i_lock);


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