Null pointer in autofs4 (_spin_lock) in 2.6.21-rc2

[Thomas Renninger]

I saw this happening several times on 2.6.21-rc2.
Tell me how I can help...
Some nfs partitions are mounted via nfs using autofs.
It takes some hours to run into this:

Unable to handle kernel NULL pointer dereference at 0000000000000008
RIP:
 [<ffffffff8025bada>] _spin_lock+0x0/0xf
PGD 1dde23067 PUD 1d3060067 PMD 0
Oops: 0002 [1] SMP
CPU 3
Modules linked in: autofs4 nfs lockd nfs_acl sunrpc asus_acpi af_packet
tg3 ipv6 button battery ac ext2 mbcache loop dm_mod floppy parport_pc lp
parport reiserfs pata_amd edd fan thermal sg processor sata_sil libata
amd74xx sd_mod scsi_mod ide_disk ide_core
Pid: 11373, comm: touch Not tainted 2.6.21-rc2-default #6
RIP: 0010:[<ffffffff8025bada>]  [<ffffffff8025bada>] _spin_lock+0x0/0xf
RSP: 0018:ffff8101c50a5a50  EFLAGS: 00010202
RAX: ffff8100eb8916f8 RBX: ffff81010007dcd8 RCX: ffff8100ea45b280
RDX: 0000000010e58c2e RSI: ffff810163bf9e50 RDI: 0000000000000008
RBP: ffff810163bf9e50 R08: ffff8101c50a4000 R09: ffff8101c50a5ea8
R10: ffff81010003fca8 R11: ffffffff802299ad R12: 0000000000000000
R13: ffff8100eb891680 R14: 0000000000000005 R15: ffff8101c50a5b48
FS:  00002b8ae744bf20(0000) GS:ffff81010016a7c0(0000)
knlGS:00000000b7bd88d0
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000008 CR3: 00000001b925f000 CR4: 00000000000006e0
Process touch (pid: 11373, threadinfo ffff8101c50a4000, task
ffff8101b78bd100)
Stack:  ffffffff882d5f38 ffff8101c50a5ea8 ffff8100ec8df4b0
00000000000000d0
 ffff8100eb8916f8 ffff810163bf9efc 10e58c2eea45b220 ffff8100ea45b220
 ffff810163bf9e50 ffff8100ea45b220 ffff8100ec8df4b0 ffff8100ec8df568
Call Trace:
 [<ffffffff882d5f38>] :autofs4:autofs4_lookup+0xcb/0x311
 [<ffffffff8020c0d8>] do_lookup+0xc4/0x1ae
 [<ffffffff802097be>] __link_path_walk+0x8ec/0xd9d
 [<ffffffff8824ca24>] :sunrpc:rpcauth_lookup_credcache+0x12e/0x24a
 [<ffffffff8020da3e>] link_path_walk+0x58/0xe0
 [<ffffffff80232d3f>] __strncpy_from_user+0x17/0x41
 [<ffffffff8020949b>] __link_path_walk+0x5c9/0xd9d
 [<ffffffff8020da3e>] link_path_walk+0x58/0xe0
 [<ffffffff80232d3f>] __strncpy_from_user+0x17/0x41
 [<ffffffff8020bea7>] do_path_lookup+0x1b6/0x217
 [<ffffffff80221512>] __path_lookup_intent_open+0x56/0x97
 [<ffffffff80218912>] open_namei+0xa9/0x64c
 [<ffffffff8025dc33>] do_page_fault+0x45e/0x7ad
 [<ffffffff802250eb>] do_filp_open+0x1c/0x38
 [<ffffffff80232d3f>] __strncpy_from_user+0x17/0x41
 [<ffffffff80217698>] do_sys_open+0x44/0xc1
 [<ffffffff8025511e>] system_call+0x7e/0x83


Code: f0 ff 0f 79 09 f3 90 83 3f 00 7e f9 eb f2 c3 f0 81 2f 00 00
RIP  [<ffffffff8025bada>] _spin_lock+0x0/0xf
 RSP <ffff8101c50a5a50>
CR2: 0000000000000008

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