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Subject: Re: 5.7.0 / BUG: kernel NULL pointer dereference / setup_cpu_watcher
To:     Christian Kujau <lists@nerdbynature.de>,
        linux-kernel@vger.kernel.org
Cc:     xen-devel@lists.xenproject.org
References: <alpine.DEB.2.22.395.2006050059530.13291@trent.utfs.org>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <7e2dec0c-8e27-6454-7793-d1246262283d@suse.com>
Date:   Fri, 5 Jun 2020 11:18:36 +0200
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On 05.06.20 10:36, Christian Kujau wrote:
> Hi,
> 
> I'm running a small Xen PVH domain and upgrading from vanilla 5.6.0 to
> 5.7.0 caused the splat below, really early during boot. The configuration
> has not changed, all new "make oldconfig" prompts have been answered with
> "N". Old and new config, dmesg are here:
> 
>    http://nerdbynature.de/bits/5.7.0/
> 
> Searching the interwebs for similar reports didn't return much:
> 
>   * drm_sched_get_cleanup_job: BUG: kernel NULL pointer dereference
>     https://bugzilla.redhat.com/show_bug.cgi?id=1822984  -- but this
>     appears to be really DRM related. - https://lkml.org/lkml/2020/4/10/545
> 
>   * A recent mm/vmstat patch, mentioning "device_offline" in its output
>     https://patchwork.kernel.org/patch/11563009/
> 
> But other than a few overlapping strings, I guess all of that is totally
> unrelated :(

Do you happen to start the guest with vcpus < maxvcpus?

If yes there is already a patch pending for 5.8:

https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git/commit/?h=for-linus-5.8&id=c54b071c192dfe8061336f650ceaf358e6386e0b


Juergen

> 
> Thanks,
> Christian.
> 
> 
> Note: that "Xen Platform PCI: unrecognised magic value" on the top appears
> in 5.6 kernels as well, but no ill effects so far.
> 
> ---------------------------------------------------------------
> Xen Platform PCI: unrecognised magic value
> ACPI: No IOAPIC entries present
> BUG: kernel NULL pointer dereference, address: 00000000000002d0
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 0 P4D 0
> Oops: 0000 [#1] SMP PTI
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.0 #2
> RIP: 0010:device_offline+0x8/0xf0
> Code: 48 89 e7 e8 3a ee f3 ff 4c 89 e0 48 83 c4 10 5b 41 5c c3 45 31 e4 48 83 c4 10 4c 89 e0 5b 41 5c c3 90 41 54 55 53 48 83 ec 10 <f6> 87 d0 02 00 00 01 0f 85 ca 00 00 00 48 89 fb 48 8b 7f 48 48 85
> RSP: 0000:ffffbd9100013e78 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00000000820001fa
> RDX: ffff9c9c3dd00000 RSI: 00000000820001fa RDI: 0000000000000000
> RBP: 0000000000000002 R08: 0000000000000001 R09: 0000000000000000
> R10: ffff9c9c3d5072a8 R11: 0000000000000000 R12: ffff9c9c3d594720
> R13: ffffffff8a57e5a8 R14: 0000000000000000 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff9c9c3dc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000000002d0 CR3: 000000006b00a001 CR4: 00000000001606b0
> Call Trace:
>   setup_cpu_watcher+0x44/0x60
>   ? plt_clk_driver_init+0xe/0xe
>   setup_vcpu_hotplug_event+0x23/0x26
>   do_one_initcall+0x47/0x180
>   kernel_init_freeable+0x13b/0x19d
>   ? rest_init+0x95/0x95
>   kernel_init+0x5/0xeb
>   ret_from_fork+0x35/0x40
> Modules linked in:
> CR2: 00000000000002d0
> ---[ end trace b0cc587db609787f ]---
>