From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Olaf Hering <olaf@aepfle.de>, xen-devel@lists.xenproject.org
Cc: Juergen Gross <jgross@suse.com>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4] xen: avoid crash in disable_hotplug_cpu
Date: Tue, 11 Sep 2018 15:39:37 -0400 [thread overview]
Message-ID: <58466174-b1a4-c5db-2e53-46c7f7a82f57@oracle.com> (raw)
In-Reply-To: <20180907143135.29608-1-olaf@aepfle.de>
On 9/7/18 10:31 AM, Olaf Hering wrote:
> The command 'xl vcpu-set 0 0', issued in dom0, will crash dom0:
>
> BUG: unable to handle kernel NULL pointer dereference at 00000000000002d8
> PGD 0 P4D 0
> Oops: 0000 [#1] PREEMPT SMP NOPTI
> CPU: 7 PID: 65 Comm: xenwatch Not tainted 4.19.0-rc2-1.ga9462db-default #1 openSUSE Tumbleweed (unreleased)
> Hardware name: Intel Corporation S5520UR/S5520UR, BIOS S5500.86B.01.00.0050.050620101605 05/06/2010
> RIP: e030:device_offline+0x9/0xb0
> Code: 77 24 00 e9 ce fe ff ff 48 8b 13 e9 68 ff ff ff 48 8b 13 e9 29 ff ff ff 48 8b 13 e9 ea fe ff ff 90 66 66 66 66 90 41 54 55 53 <f6> 87 d8 02 00 00 01 0f 85 88 00 00 00 48 c7 c2 20 09 60 81 31 f6
> RSP: e02b:ffffc90040f27e80 EFLAGS: 00010203
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff8801f3800000 RSI: ffffc90040f27e70 RDI: 0000000000000000
> RBP: 0000000000000000 R08: ffffffff820e47b3 R09: 0000000000000000
> R10: 0000000000007ff0 R11: 0000000000000000 R12: ffffffff822e6d30
> R13: dead000000000200 R14: dead000000000100 R15: ffffffff8158b4e0
> FS: 00007ffa595158c0(0000) GS:ffff8801f39c0000(0000) knlGS:0000000000000000
> CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000000002d8 CR3: 00000001d9602000 CR4: 0000000000002660
> Call Trace:
> handle_vcpu_hotplug_event+0xb5/0xc0
> xenwatch_thread+0x80/0x140
> ? wait_woken+0x80/0x80
> kthread+0x112/0x130
> ? kthread_create_worker_on_cpu+0x40/0x40
> ret_from_fork+0x3a/0x50
>
> This happens because handle_vcpu_hotplug_event is called twice. In the
> first iteration cpu_present is still true, in the second iteration
> cpu_present is false which causes get_cpu_device to return NULL.
> In case of cpu#0, cpu_online is apparently always true.
>
> Fix this crash by checking if the cpu can be hotplugged, which is false
> for a cpu that was just removed.
>
> Also check if the cpu was actually offlined by device_remove, otherwise
> leave the cpu_present state as it is.
>
> Rearrange to code to do all work with device_hotplug_lock held.
>
> Signed-off-by: Olaf Hering <olaf@aepfle.de>
Applied to for-linus-4.19b
-boris
prev parent reply other threads:[~2018-09-11 19:38 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-07 14:31 Olaf Hering
2018-09-07 14:34 ` Juergen Gross
2018-09-07 16:56 ` Boris Ostrovsky
2018-09-10 15:58 ` Olaf Hering
2018-09-10 17:55 ` Boris Ostrovsky
2018-09-11 7:52 ` Olaf Hering
2018-09-11 7:55 ` Juergen Gross
2018-09-11 10:48 ` Olaf Hering
2018-09-11 10:51 ` Juergen Gross
2018-09-11 19:39 ` Boris Ostrovsky [this message]
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