Re: [PATCH] SLUB: clear c->freelist in __slab_alloc()/load_freelist:/SlabDebugpath

From: Benny Halevy
Date: Tue May 13 2008 - 15:35:32 EST

On May. 13, 2008, 11:40 -0700, "Pekka Enberg" <penberg@xxxxxxxxxxxxxx> wrote:
> Hi Benny,
>
> On Mon, May 12, 2008 at 11:32 PM, Benny Halevy <bhalevy@xxxxxxxxxxx> wrote:
>> In the __slab_alloc()/load_freelist:/SlabDebug(c->page) path we only
>> use the object at the head of c->page->freelist
>> and the tail goes back to c->page->freelist.
>> We then set c->node = -1 to force __slab_alloc in next allocation.
>> c->freelist therefore needs to be cleared as it is invalid at this point.
>
> But for debug pages, we never load c->page->freelist to c->freelist so
> it should always be NULL.

Hmm, I see. Then it might have got corrupted...
I'll keep looking for the root cause.

Benny

>
>> Signed-off-by: Benny Halevy <bhalevy@xxxxxxxxxxx>
>> ---
>> mm/slub.c | 1 +
>> 1 files changed, 1 insertions(+), 0 deletions(-)
>>
>> Hit while running cthon04 test from an IBM AIX client
>> against my nfs41 tree.
>>
>> Stack trace excerpt:
>>
>> May 12 11:18:19 client kernel: general protection fault: 0000 [2] SMP
>> May 12 11:18:19 client kernel: CPU 3
>> May 12 11:18:19 client kernel: Modules linked in: panfs(P) nfsd auth_rpcgss exportfs autofs4 hidp nfs lockd nfs_acl fuse rfcomm l2cap bluetooth sunrpc nf_conntrack_netbios_ns nf_conntrack_ipv4 ipt_REJECT iptable_filter ip_tables nf_conntrack_ipv6 xt_state nf_conntrack xt_tcpudp ip6t_ipv6header ip6t_REJECT ip6table_filter ip6_tables x_tables ipv6 dm_multipath video output sbs sbshc battery ac e1000e i5000_edac iTCO_wdt iTCO_vendor_support i2c_i801 edac_core button sr_mod pcspkr i2c_core sg cdrom floppy dm_snapshot dm_zero dm_mirror dm_mod ata_piix libata shpchp pci_hotplug mptsas mptscsih mptbase scsi_transport_sas sd_mod scsi_mod ext3 jbd mbcache ehci_hcd ohci_hcd uhci_hcd [last unloaded: microcode]
>> May 12 11:18:19 client kernel: Pid: 2815, comm: nfsd Tainted: P D 2.6.25-nfs41 #2
>> May 12 11:18:19 client kernel: RIP: 0010:[<ffffffff8108c0c8>] [<ffffffff8108c0c8>] kmem_cache_alloc+0x3d/0x65
>> May 12 11:18:19 client kernel: RSP: 0018:ffff8104212c3de0 EFLAGS: 00010006
>> May 12 11:18:19 client kernel: RAX: 0000000000000000 RBX: 0000000000000246 RCX: ffffffff883546df
>> May 12 11:18:19 client kernel: RDX: 3200100010100000 RSI: 00000000000080d0 RDI: ffffffff813eadb8
>> May 12 11:18:19 client kernel: RBP: ffff810001029e60 R08: 0000000000000000 R09: ffff8103f118d130
>> May 12 11:18:19 client kernel: R10: ffff81041b076018 R11: ffffffff8826c313 R12: 00000000000080d0
>> May 12 11:18:19 client kernel: R13: ffff8104211aa000 R14: ffff81041b076000 R15: ffff8104239c8000
>> May 12 11:18:19 client kernel: FS: 00007f08fb8626f0(0000) GS:ffff81042fc02e80(0000) knlGS:0000000000000000
>> May 12 11:18:19 client kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> May 12 11:18:19 client kernel: CR2: 00007fdaf41cf030 CR3: 0000000420827000 CR4: 00000000000006e0
>> May 12 11:18:19 client kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> May 12 11:18:19 client kernel: DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>> May 12 11:18:19 client kernel: Process nfsd (pid: 2815, threadinfo ffff8104212c2000, task ffff81042381c940)
>> May 12 11:18:19 client kernel: Stack: ffff8104211ab000 ffff8103f118d000 0000000022270000 ffffffff883546df
>> May 12 11:18:19 client kernel: ffffffff88373cb8 0000000000000000 ffff8103f118d130 ffff8104239c8000
>> May 12 11:18:19 client kernel: ffffffff88373cb8 000000000000001c ffff81041b076018 ffff81041b076000
>> May 12 11:18:19 client kernel: Call Trace:
>> May 12 11:18:19 client kernel: [<ffffffff883546df>] ? :nfsd:nfsd4_proc_compound+0xa9/0x3f6
>> May 12 11:18:19 client kernel: [<ffffffff88346245>] ? :nfsd:nfsd_dispatch+0xde/0x1b6
>> May 12 11:18:19 client kernel: [<ffffffff88268bb7>] ? :sunrpc:svc_process_common+0x2e8/0x5a9
>> May 12 11:18:19 client kernel: [<ffffffff8834667c>] ? :nfsd:nfsd+0x0/0x2b4
>> May 12 11:18:19 client kernel: [<ffffffff88269d16>] ? :sunrpc:svc_process+0x127/0x13d
>> May 12 11:18:19 client kernel: [<ffffffff88346819>] ? :nfsd:nfsd+0x19d/0x2b4May 12 11:18:19 client kernel: [<ffffffff8100cac8>] ? child_rip+0xa/0x12
>> May 12 11:18:19 client kernel: [<ffffffff8834667c>] ? :nfsd:nfsd+0x0/0x2b4
>> May 12 11:18:19 client last message repeated 2 times
>> May 12 11:18:19 client kernel: [<ffffffff8100cabe>] ? child_rip+0x0/0x12
>> May 12 11:18:19 client kernel:
>> May 12 11:18:19 client kernel:
>> May 12 11:18:19 client kernel: Code: 25 24 00 00 00 48 98 48 8b ac c7 d8 02 00 00 48 8b 55 00 48 85 d2 75 10 83 ca ff 49 89 e8 e8 7e f8 ff ff 48 89 c2 eb 0b 8b 45 14 <48> 8b 04 c2 48 89 45 00 53 9d 66 45 85 e4 79 10 48 85 d2 74 0b
>> May 12 11:18:19 client kernel: RIP [<ffffffff8108c0c8>] kmem_cache_alloc+0x3d/0x65
>> May 12 11:18:19 client kernel: RSP <ffff8104212c3de0>
>> May 12 11:18:19 client kernel: ---[ end trace 9b6f5806f68a2b8c ]---
>>
>> $ grep SL.B .config
>> CONFIG_SLUB_DEBUG=y
>> # CONFIG_SLAB is not set
>> CONFIG_SLUB=y
>> # CONFIG_SLOB is not set
>> CONFIG_SLABINFO=y
>> # CONFIG_SLUB_DEBUG_ON is not set
>> # CONFIG_SLUB_STATS is not set
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index a505a82..0d1d820 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -1606,6 +1606,7 @@ debug:
>> if (!alloc_debug_processing(s, c->page, object, addr))
>> goto another_slab;
>>
>> + c->freelist = NULL;
>> c->page->inuse++;
>> c->page->freelist = object[c->offset];
>> c->node = -1;
>
> Looking at this, we're oopsing at:
>
> 0: 48 8b 04 c2 mov (%rdx,%rax,8),%rax
>
> where rdx is c->freelist and rax c->offset. The the value for
> c->freelist ("3200100010100000") doesn't make much sense. Furthermore,
> we never if this really were a bug in __slab_alloc() shouldn't we be
> hitting it more often?
>
> How did you make SLUB hit the debug path since you have
> CONFIG_SLUB_DEBUG_ON disabled?
>
> Pekka

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/