On 10/12/19 10:46 AM, Stefan Hajnoczi wrote:
> On Fri, Oct 11, 2019 at 06:08:34AM -0600, Jens Axboe wrote:
>> On 10/11/19 2:46 AM, Stefan Hajnoczi wrote:
>>> On Wed, Oct 09, 2019 at 02:36:01PM -0600, Jens Axboe wrote:
>>>> On 10/9/19 11:46 AM, Stefan Hajnoczi wrote:
>>>>> On Wed, Oct 09, 2019 at 05:27:44AM -0600, Jens Axboe wrote:
>>>>>> On 10/9/19 3:23 AM, Stefan Hajnoczi wrote:
>>>>>>> I hit this NULL pointer dereference when running qemu-iotests 052 (raw)
>>>>>>> on both ext4 and XFS on dm-thin/luks. The kernel is Linux v5.4-rc1 but
>>>>>>> I haven't found any obvious fixes in Jens' tree, so it's likely that
>>>>>>> this bug is still present:
>>>>>>>
>>>>>>> BUG: kernel NULL pointer dereference, address: 0000000000000102
>>>>>>> #PF: supervisor read access in kernel mode
>>>>>>> #PF: error_code(0x0000) - not-present page
>>>>>>> PGD 0 P4D 0
>>>>>>> Oops: 0000 [#1] SMP PTI
>>>>>>> CPU: 2 PID: 6656 Comm: qemu-io Not tainted 5.4.0-rc1 #1
>>>>>>> Hardware name: LENOVO 20BTS1N70V/20BTS1N70V, BIOS N14ET37W (1.15 ) 09/06/2016
>>>>>>> RIP: 0010:__queue_work+0x1f/0x3b0
>>>>>>> Code: eb df 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 57 49 89 f7 41 56 41 89 fe 41 55 41 89 fd 41 54 55 48 89 d5 53 48 83 ec 10 <f6> 86 02 01 00 00 01 0f 85 bc 02 00 00 49 bc eb 83 b5 80 46 86 c8
>>>>>>> RSP: 0018:ffffbef4884bbd58 EFLAGS: 00010082
>>>>>>> RAX: 0000000000000246 RBX: 0000000000000246 RCX: 0000000000000000
>>>>>>> RDX: ffff9903901f4460 RSI: 0000000000000000 RDI: 0000000000000040
>>>>>>> RBP: ffff9903901f4460 R08: ffff9903901fb040 R09: ffff990398614700
>>>>>>> R10: 0000000000000030 R11: 0000000000000000 R12: 0000000000000000
>>>>>>> R13: 0000000000000040 R14: 0000000000000040 R15: 0000000000000000
>>>>>>> FS: 00007f7d2a4e4a80(0000) GS:ffff9903a5a80000(0000) knlGS:0000000000000000
>>>>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>>> CR2: 0000000000000102 CR3: 0000000203da8004 CR4: 00000000003606e0
>>>>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>>>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>>>>>> Call Trace:
>>>>>>> ? __io_queue_sqe+0xa1/0x200
>>>>>>> queue_work_on+0x36/0x40
>>>>>>> __io_queue_sqe+0x16e/0x200
>>>>>>> io_ring_submit+0xd2/0x230
>>>>>>> ? percpu_ref_resurrect+0x46/0x70
>>>>>>> ? __io_uring_register+0x207/0xa30
>>>>>>> ? __schedule+0x286/0x700
>>>>>>> __x64_sys_io_uring_enter+0x1a3/0x280
>>>>>>> ? __x64_sys_io_uring_register+0x64/0xb0
>>>>>>> do_syscall_64+0x5b/0x180
>>>>>>> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>>>>> RIP: 0033:0x7f7d3439f1fd
>>>>>>> Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 5b 8c 0c 00 f7 d8 64 89 01 48
>>>>>>> RSP: 002b:00007f7d2918d408 EFLAGS: 00000216 ORIG_RAX: 00000000000001aa
>>>>>>> RAX: ffffffffffffffda RBX: 00007f7d2918d4f0 RCX: 00007f7d3439f1fd
>>>>>>> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 000000000000000a
>>>>>>> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000008
>>>>>>> R10: 0000000000000000 R11: 0000000000000216 R12: 00005616e3c32ab8
>>>>>>> R13: 00005616e3c32b78 R14: 00005616e3c32ab0 R15: 0000000000000001
>>>>>>> Modules linked in: fuse ccm xt_CHECKSUM xt_MASQUERADE tun bridge stp llc nf_conntrack_netbios_ns nf_conntrack_broadcast xt_CT ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat iptable_mangle iptable_raw iptable_security nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nfnetlink ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables sunrpc vfat fat intel_rapl_msr rmi_smbus iwlmvm rmi_core intel_rapl_common x86_pkg_temp_thermal intel_powerclamp coretemp mac80211 snd_hda_codec_realtek snd_hda_codec_generic snd_hda_codec_hdmi kvm_intel snd_hda_intel kvm snd_intel_nhlt snd_hda_codec snd_usb_audio irqbypass uvcvideo snd_hda_core snd_usbmidi_lib snd_rawmidi iTCO_wdt snd_hwdep libarc4 intel_cstate cdc_ether intel_uncore videobuf2_vmalloc iwlwifi mei_wdt mei_hdcp iTCO_vendor_support snd_seq videobuf2_memops usbnet videobuf2_v4l2 snd_seq_device
>>>>>>> intel_rapl_perf pcspkr videobuf2_common joydev wmi_bmof snd_pcm cfg80211 r8152 videodev intel_pch_thermal i2c_i801 mii mc thinkpad_acpi snd_timer mei_me ledtrig_audio snd lpc_ich mei soundcore rfkill binfmt_misc xfs dm_thin_pool dm_persistent_data dm_bio_prison libcrc32c dm_crypt i915 i2c_algo_bit drm_kms_helper drm crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel serio_raw wmi video
>>>>>>> CR2: 0000000000000102
>>>>>>> ---[ end trace 2ac747acabe218da ]---
>>>>>>> RIP: 0010:__queue_work+0x1f/0x3b0
>>>>>>> Code: eb df 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 57 49 89 f7 41 56 41 89 fe 41 55 41 89 fd 41 54 55 48 89 d5 53 48 83 ec 10 <f6> 86 02 01 00 00 01 0f 85 bc 02 00 00 49 bc eb 83 b5 80 46 86 c8
>>>>>>> RSP: 0018:ffffbef4884bbd58 EFLAGS: 00010082
>>>>>>> RAX: 0000000000000246 RBX: 0000000000000246 RCX: 0000000000000000
>>>>>>> RDX: ffff9903901f4460 RSI: 0000000000000000 RDI: 0000000000000040
>>>>>>> RBP: ffff9903901f4460 R08: ffff9903901fb040 R09: ffff990398614700
>>>>>>> R10: 0000000000000030 R11: 0000000000000000 R12: 0000000000000000
>>>>>>> R13: 0000000000000040 R14: 0000000000000040 R15: 0000000000000000
>>>>>>> FS: 00007f7d2a4e4a80(0000) GS:ffff9903a5a80000(0000) knlGS:0000000000000000
>>>>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>>> CR2: 0000000000000102 CR3: 0000000203da8004 CR4: 00000000003606e0
>>>>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>>>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>>>>>>
>>>>>>> Unfortunately I don't have time to find the root cause. What I've
>>>>>>> figured out so far is:
>>>>>>>
>>>>>>> bool queue_work_on(int cpu, struct workqueue_struct *wq,
>>>>>>> struct work_struct *work)
>>>>>>> {
>>>>>>> bool ret = false;
>>>>>>> unsigned long flags;
>>>>>>>
>>>>>>> local_irq_save(flags);
>>>>>>>
>>>>>>> if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
>>>>>>> ~~~~~~~~~~~~~~~~~~~~
>>>>>>>
>>>>>>> The address of work is 0x102 so this line causes a page fault when it
>>>>>>> tries to access the data field (offset 0).
>>>>>>>
>>>>>>> The caller provided the 0x102 pointer so let's see where it comes from:
>>>>>>>
>>>>>>> static int __io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
>>>>>>> struct sqe_submit *s, bool force_nonblock)
>>>>>>> {
>>>>>>> ...
>>>>>>> if (!io_add_to_prev_work(list, req)) {
>>>>>>> if (list)
>>>>>>> atomic_inc(&list->cnt);
>>>>>>> INIT_WORK(&req->work, io_sq_wq_submit_work);
>>>>>>> io_queue_async_work(ctx, req);
>>>>>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>>>
>>>>>>> and queue_work() is called here:
>>>>>>>
>>>>>>> static inline void io_queue_async_work(struct io_ring_ctx *ctx,
>>>>>>> struct io_kiocb *req)
>>>>>>> {
>>>>>>> int rw = 0;
>>>>>>>
>>>>>>> if (req->submit.sqe) {
>>>>>>> switch (req->submit.sqe->opcode) {
>>>>>>> case IORING_OP_WRITEV:
>>>>>>> case IORING_OP_WRITE_FIXED:
>>>>>>> rw = !(req->rw.ki_flags & IOCB_DIRECT);
>>>>>>> break;
>>>>>>> }
>>>>>>> }
>>>>>>>
>>>>>>> queue_work(ctx->sqo_wq[rw], &req->work);
>>>>>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>>>
>>>>>>> I must be missing something though because it seems impossible to get
>>>>>>> this far if req is NULL. INIT_WORK() would have Oopsed already. Also,
>>>>>>> offsetof(struct io_kiocb, work) is 0xa0 according to pahole(1) so we
>>>>>>> still haven't reached the 0x102 offset from the Oops report.
>>>>>>>
>>>>>>> Any ideas?
>>>>>>
>>>>>> This is new in 5.4-rc1?
>>>>>
>>>>> I didn't hit it with 5.3, but I hit other issues so I'm not sure if this
>>>>> bug exists in older kernels.
>>>>>
>>>>>> And how are you reproducing it?
>>>>>
>>>>> $ git clone -b io_uring https://github.com/stefanha/qemu
>>>>> $ cd qemu
>>>>> $ ./configure --target-list=x86_64-softmmu
>>>>> $ make -j$(nproc)
>>>>> $ (cd tests/qemu-iotests && ./check -i io_uring 052)
>>>>>
>>>>> You can mount the file system of your choice at
>>>>> tests/qemu-iotests/scratch/ before running the test.
>>>>>
>>>>> You can view the test case at tests/qemu-iotests/052.
>>>>
>>>> Thanks, that's useful. Need to look closer into this, but seems wrong
>>>> that we're killing the workqueue for SCM_RIGHTS removal. We just need to
>>>> sync it. Does this work for you?
>>>>
>>>>
>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>> index 8a0381f1a43b..a8755582c688 100644
>>>> --- a/fs/io_uring.c
>>>> +++ b/fs/io_uring.c
>>>> @@ -2920,8 +2920,12 @@ static void io_finish_async(struct io_ring_ctx *ctx)
>>>> static void io_destruct_skb(struct sk_buff *skb)
>>>> {
>>>> struct io_ring_ctx *ctx = skb->sk->sk_user_data;
>>>> + int i;
>>>> +
>>>> + for (i = 0; i < ARRAY_SIZE(ctx->sqo_wq); i++)
>>>> + if (ctx->sqo_wq[i])
>>>> + flush_workqueue(ctx->sqo_wq[i]);
>>>>
>>>> - io_finish_async(ctx);
>>>> unix_destruct_scm(skb);
>>>> }
>>>
>>> I tried this patch but still hit the same NULL pointer dereference.
>>
>> How certain are you that you booted the right kernel when you tested
>> that? Because I'm very certain that this patch will fix the issue you
>> saw.
>>
>> You can also pull:
>>
>> git://git.kernel.dk/linux-block for-linus
>>
>> into master and test that.
>
> It was bugging me that we don't know if Linux v5.4-rc1 has a regression,
> so I merged your for-linux branch on top of Linux v5.4-rc1 as you
> suggested.
>
> The test passes, so it's now certain that the fix(es) in your for-linux
> branch solve the NULL pointer dereference :).
Thanks for double checking! It's not a recent regression, it's been
there a while. But it does depend on timing for your test case, so maybe
why you haven't seen it before. In any case, it's fixed in Linus's tree
now.
--
Jens Axboe
