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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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