Re: Kernel oops with 6.14 when enabling TLS

[Hannes Reinecke <hare@suse.de>]

On 3/4/25 16:29, Vlastimil Babka wrote:
> On 3/4/25 11:26, Vlastimil Babka wrote:
>> +Cc NETWORKING [TLS] maintainers and netdev for input, thanks.
>>
>> The full error is here:
>> https://lore.kernel.org/all/fcfa11c6-2738-4a2e-baa8-09fa8f79cbf3@suse.de/
>>
>> On 3/4/25 11:20, Hannes Reinecke wrote:
>>> On 3/4/25 09:18, Vlastimil Babka wrote:
>>>> On 3/4/25 08:58, Hannes Reinecke wrote:
>>>>> On 3/3/25 23:02, Vlastimil Babka wrote:
>>>>>> On 3/3/25 17:15, Vlastimil Babka wrote:
>>>>>>> On 3/3/25 16:48, Matthew Wilcox wrote:
>>>>>>>> You need to turn on the debugging options Vlastimil mentioned and try to
>>>>>>>> figure out what nvme is doing wrong.
>>>>>>>
>>>>>>> Agree, looks like some error path going wrong?
>>>>>>> Since there seems to be actual non-large kmalloc usage involved, another
>>>>>>> debug parameter that could help: CONFIG_SLUB_DEBUG=y, and boot with
>>>>>>> "slab_debug=FZPU,kmalloc-*"
>>>>>>
>>>>>> Also make sure you have CONFIG_DEBUG_VM please.
>>>>>>
>>>>> Here you go:
>>>>>
>>>>> [  134.506802] page: refcount:0 mapcount:0 mapping:0000000000000000
>>>>> index:0x0 pfn:0x101ef8
>>>>> [  134.509253] head: order:3 mapcount:0 entire_mapcount:0
>>>>> nr_pages_mapped:0 pincount:0
>>>>> [  134.511594] flags:
>>>>> 0x17ffffc0000040(head|node=0|zone=2|lastcpupid=0x1fffff)
>>>>> [  134.513556] page_type: f5(slab)
>>>>> [  134.513563] raw: 0017ffffc0000040 ffff888100041b00 ffffea0004a90810
>>>>> ffff8881000402f0
>>>>> [  134.513568] raw: 0000000000000000 00000000000a000a 00000000f5000000
>>>>> 0000000000000000
>>>>> [  134.513572] head: 0017ffffc0000040 ffff888100041b00 ffffea0004a90810
>>>>> ffff8881000402f0
>>>>> [  134.513575] head: 0000000000000000 00000000000a000a 00000000f5000000
>>>>> 0000000000000000
>>>>> [  134.513579] head: 0017ffffc0000003 ffffea000407be01 ffffffffffffffff
>>>>> 0000000000000000
>>>>> [  134.513583] head: 0000000000000008 0000000000000000 00000000ffffffff
>>>>> 0000000000000000
>>>>> [  134.513585] page dumped because: VM_BUG_ON_FOLIO(((unsigned int)
>>>>> folio_ref_count(folio) + 127u <= 127u))
>>>>> [  134.513615] ------------[ cut here ]------------
>>>>> [  134.529822] kernel BUG at ./include/linux/mm.h:1455!
>>>>
>>>> Yeah, just as I suspected, folio_get() says the refcount is 0.
>>>>
>>>>> [  134.529835] Oops: invalid opcode: 0000 [#1] PREEMPT SMP
>>>>> DEBUG_PAGEALLOC NOPTI
>>>>> [  134.529843] CPU: 0 UID: 0 PID: 274 Comm: kworker/0:1H Kdump: loaded
>>>>> Tainted: G            E      6.14.0-rc4-default+ #309
>>>>> 03b131f1ef70944969b40df9d90a283ed638556f
>>>>> [  134.536577] Tainted: [E]=UNSIGNED_MODULE
>>>>> [  134.536580] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
>>>>> 0.0.0 02/06/2015
>>>>> [  134.536583] Workqueue: nvme_tcp_wq nvme_tcp_io_work [nvme_tcp]
>>>>> [  134.536595] RIP: 0010:__iov_iter_get_pages_alloc+0x676/0x710
>>>>> [  134.542810] Code: e8 4c 39 e0 49 0f 47 c4 48 01 45 08 48 29 45 18 e9
>>>>> 90 fa ff ff 48 83 ef 01 e9 7f fe ff ff 48 c7 c6 40 57 4f 82 e8 6a e2 ce
>>>>> ff <0f> 0b e8 43 b8 b1 ff eb c5 f7 c1 ff 0f 00 00 48 89 cf 0f 85 4f ff
>>>>> [  134.542816] RSP: 0018:ffffc900004579d8 EFLAGS: 00010282
>>>>> [  134.542821] RAX: 000000000000005c RBX: ffffc90000457a90 RCX:
>>>>> 0000000000000027
>>>>> [  134.542825] RDX: 0000000000000000 RSI: 0000000000000002 RDI:
>>>>> ffff88817f423748
>>>>> [  134.542828] RBP: ffffc90000457d60 R08: 0000000000000000 R09:
>>>>> 0000000000000001
>>>>> [  134.554485] R10: ffffc900004579c0 R11: ffffc90000457720 R12:
>>>>> 0000000000000000
>>>>> [  134.554488] R13: ffffea000407be40 R14: ffffc90000457a70 R15:
>>>>> ffffc90000457d60
>>>>> [  134.554495] FS:  0000000000000000(0000) GS:ffff88817f400000(0000)
>>>>> knlGS:0000000000000000
>>>>> [  134.554499] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>> [  134.554502] CR2: 0000556b0675b600 CR3: 0000000106bd8000 CR4:
>>>>> 0000000000350ef0
>>>>> [  134.554509] Call Trace:
>>>>> [  134.554512]  <TASK>
>>>>> [  134.554516]  ? __die_body+0x1a/0x60
>>>>> [  134.554525]  ? die+0x38/0x60
>>>>> [  134.554531]  ? do_trap+0x10f/0x120
>>>>> [  134.554538]  ? __iov_iter_get_pages_alloc+0x676/0x710
>>>>> [  134.568839]  ? do_error_trap+0x64/0xa0
>>>>> [  134.568847]  ? __iov_iter_get_pages_alloc+0x676/0x710
>>>>> [  134.568855]  ? exc_invalid_op+0x53/0x60
>>>>> [  134.572489]  ? __iov_iter_get_pages_alloc+0x676/0x710
>>>>> [  134.572496]  ? asm_exc_invalid_op+0x16/0x20
>>>>> [  134.572512]  ? __iov_iter_get_pages_alloc+0x676/0x710
>>>>> [  134.576726]  ? __iov_iter_get_pages_alloc+0x676/0x710
>>>>> [  134.576733]  ? srso_return_thunk+0x5/0x5f
>>>>> [  134.576740]  ? ___slab_alloc+0x924/0xb60
>>>>> [  134.580253]  ? mempool_alloc_noprof+0x41/0x190
>>>>> [  134.580262]  ? tls_get_rec+0x3d/0x1b0 [tls
>>>>> 47f199c97f69357468c91efdbba24395e9dbfa77]
>>>>> [  134.580282]  iov_iter_get_pages2+0x19/0x30
>>>>
>>>> Presumably that's __iov_iter_get_pages_alloc() doing get_page() either in
>>>> the " if (iov_iter_is_bvec(i)) " branch or via iter_folioq_get_pages()?
>>>>
>>> Looks like it.
>>>
>>>> Which doesn't work for a sub-size kmalloc() from a slab folio, which after
>>>> the frozen refcount conversion no longer supports get_page().
>>>>
>>>> The question is if this is a mistake specific for this path that's easy to
>>>> fix or there are more paths that do this. At the very least the pinning of
>>>> page through a kmalloc() allocation from it is useless - the object itself
>>>> has to be kfree()'d and that would never happen through a put_page()
>>>> reaching zero.
>>>>
>>> Looks like a specific mistake.
>>> tls_sw is the only user of sk_msg_zerocopy_from_iter()
>>> (which is calling into __iov_iter_get_pages_alloc()).
> 
> That's from tls_sw_sendmsg_locked(), right? But that's under:
> 
> if (!is_kvec && (full_record || eor) && !async_capable) {
> 
> Shouldn't is_kvec be true if we're dealing a kernel buffer (kmalloc()) there?
> 
Yes, and no.

We're initializing the iter in nvme_tcp_try_send_data():

		bvec_set_page(&bvec, page, len, offset);
		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, len);

and 'page' is coming from bio bvec. So the bv_page could refer to a 
kmalloced page, the bvec is still that, a bvec.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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