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From:   "Zengtao (B)" <prime.zeng@hisilicon.com>
To:     Cornelia Huck <cohuck@redhat.com>
CC:     "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
        "cai@lca.pw" <cai@lca.pw>, Kevin Tian <kevin.tian@intel.com>,
        Peter Xu <peterx@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Michel Lespinasse" <walken@google.com>,
        Denis Efremov <efremov@linux.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] vfio/pci: fix racy on error and request eventfd ctx
Thread-Topic: [PATCH] vfio/pci: fix racy on error and request eventfd ctx
Thread-Index: AQHWWnqQ+QrCfngfhUOguFGy1o0RgqkH7XyAgACJOHA=
Date:   Wed, 15 Jul 2020 11:06:04 +0000
Message-ID: <678F3D1BB717D949B966B68EAEB446ED415845CF@dggemm526-mbx.china.huawei.com>
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 <20200715123955.0d7e731a.cohuck@redhat.com>
In-Reply-To: <20200715123955.0d7e731a.cohuck@redhat.com>
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> -----Original Message-----
> From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org]
> On Behalf Of Cornelia Huck
> Sent: Wednesday, July 15, 2020 6:40 PM
> To: Zengtao (B)
> Cc: alex.williamson@redhat.com; cai@lca.pw; Kevin Tian; Peter Xu;
> Andrew Morton; Michel Lespinasse; Denis Efremov; kvm@vger.kernel.org;
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH] vfio/pci: fix racy on error and request eventfd ctx
> 
> On Wed, 15 Jul 2020 15:34:41 +0800
> Zeng Tao <prime.zeng@hisilicon.com> wrote:
> 
> > The vfio_pci_release call will free and clear the error and request
> > eventfd ctx while these ctx could be in use at the same time in the
> > function like vfio_pci_request, and it's expected to protect them under
> > the vdev->igate mutex, which is missing in vfio_pci_release.
> >
> > This issue is introduced since commit 1518ac272e78 ("vfio/pci: fix
> memory
> > leaks of eventfd ctx"),and since commit 5c5866c593bb ("vfio/pci: Clear
> > error and request eventfd ctx after releasing"), it's very easily to
> > trigger the kernel panic like this:
> >
> > [ 9513.904346] Unable to handle kernel NULL pointer dereference at
> virtual address 0000000000000008
> > [ 9513.913091] Mem abort info:
> > [ 9513.915871]   ESR = 0x96000006
> > [ 9513.918912]   EC = 0x25: DABT (current EL), IL = 32 bits
> > [ 9513.924198]   SET = 0, FnV = 0
> > [ 9513.927238]   EA = 0, S1PTW = 0
> > [ 9513.930364] Data abort info:
> > [ 9513.933231]   ISV = 0, ISS = 0x00000006
> > [ 9513.937048]   CM = 0, WnR = 0
> > [ 9513.940003] user pgtable: 4k pages, 48-bit VAs,
> pgdp=0000007ec7d12000
> > [ 9513.946414] [0000000000000008] pgd=0000007ec7d13003,
> p4d=0000007ec7d13003, pud=0000007ec728c003,
> pmd=0000000000000000
> > [ 9513.956975] Internal error: Oops: 96000006 [#1] PREEMPT SMP
> > [ 9513.962521] Modules linked in: vfio_pci vfio_virqfd vfio_iommu_type1
> vfio hclge hns3 hnae3 [last unloaded: vfio_pci]
> > [ 9513.972998] CPU: 4 PID: 1327 Comm: bash Tainted: G        W
> 5.8.0-rc4+ #3
> > [ 9513.980443] Hardware name: Huawei TaiShan 2280 V2/BC82AMDC,
> BIOS 2280-V2 CS V3.B270.01 05/08/2020
> > [ 9513.989274] pstate: 80400089 (Nzcv daIf +PAN -UAO BTYPE=--)
> > [ 9513.994827] pc : _raw_spin_lock_irqsave+0x48/0x88
> > [ 9513.999515] lr : eventfd_signal+0x6c/0x1b0
> > [ 9514.003591] sp : ffff800038a0b960
> > [ 9514.006889] x29: ffff800038a0b960 x28: ffff007ef7f4da10
> > [ 9514.012175] x27: ffff207eefbbfc80 x26: ffffbb7903457000
> > [ 9514.017462] x25: ffffbb7912191000 x24: ffff007ef7f4d400
> > [ 9514.022747] x23: ffff20be6e0e4c00 x22: 0000000000000008
> > [ 9514.028033] x21: 0000000000000000 x20: 0000000000000000
> > [ 9514.033321] x19: 0000000000000008 x18: 0000000000000000
> > [ 9514.038606] x17: 0000000000000000 x16: ffffbb7910029328
> > [ 9514.043893] x15: 0000000000000000 x14: 0000000000000001
> > [ 9514.049179] x13: 0000000000000000 x12: 0000000000000002
> > [ 9514.054466] x11: 0000000000000000 x10: 0000000000000a00
> > [ 9514.059752] x9 : ffff800038a0b840 x8 : ffff007ef7f4de60
> > [ 9514.065038] x7 : ffff007fffc96690 x6 : fffffe01faffb748
> > [ 9514.070324] x5 : 0000000000000000 x4 : 0000000000000000
> > [ 9514.075609] x3 : 0000000000000000 x2 : 0000000000000001
> > [ 9514.080895] x1 : ffff007ef7f4d400 x0 : 0000000000000000
> > [ 9514.086181] Call trace:
> > [ 9514.088618]  _raw_spin_lock_irqsave+0x48/0x88
> > [ 9514.092954]  eventfd_signal+0x6c/0x1b0
> > [ 9514.096691]  vfio_pci_request+0x84/0xd0 [vfio_pci]
> > [ 9514.101464]  vfio_del_group_dev+0x150/0x290 [vfio]
> > [ 9514.106234]  vfio_pci_remove+0x30/0x128 [vfio_pci]
> > [ 9514.111007]  pci_device_remove+0x48/0x108
> > [ 9514.115001]  device_release_driver_internal+0x100/0x1b8
> > [ 9514.120200]  device_release_driver+0x28/0x38
> > [ 9514.124452]  pci_stop_bus_device+0x68/0xa8
> > [ 9514.128528]  pci_stop_and_remove_bus_device+0x20/0x38
> > [ 9514.133557]  pci_iov_remove_virtfn+0xb4/0x128
> > [ 9514.137893]  sriov_disable+0x3c/0x108
> > [ 9514.141538]  pci_disable_sriov+0x28/0x38
> > [ 9514.145445]  hns3_pci_sriov_configure+0x48/0xb8 [hns3]
> > [ 9514.150558]  sriov_numvfs_store+0x110/0x198
> > [ 9514.154724]  dev_attr_store+0x44/0x60
> > [ 9514.158373]  sysfs_kf_write+0x5c/0x78
> > [ 9514.162018]  kernfs_fop_write+0x104/0x210
> > [ 9514.166010]  __vfs_write+0x48/0x90
> > [ 9514.169395]  vfs_write+0xbc/0x1c0
> > [ 9514.172694]  ksys_write+0x74/0x100
> > [ 9514.176079]  __arm64_sys_write+0x24/0x30
> > [ 9514.179987]  el0_svc_common.constprop.4+0x110/0x200
> > [ 9514.184842]  do_el0_svc+0x34/0x98
> > [ 9514.188144]  el0_svc+0x14/0x40
> > [ 9514.191185]  el0_sync_handler+0xb0/0x2d0
> > [ 9514.195088]  el0_sync+0x140/0x180
> > [ 9514.198389] Code: b9001020 d2800000 52800022 f9800271
> (885ffe61)
> > [ 9514.204455] ---[ end trace 648de00c8406465f ]---
> > [ 9514.212308] note: bash[1327] exited with preempt_count 1
> 
> Good catch, I hope this is fixed now for good :/
> 
> >
> > Cc: Qian Cai <cai@lca.pw>
> > Cc: Alex Williamson <alex.williamson@redhat.com>
> > Fixes: 1518ac272e78 ("vfio/pci: fix memory leaks of eventfd ctx")
> 
> Fixes: 5c5866c593bb ("vfio/pci: Clear error and request eventfd ctx after
> releasing")
> 
In fact, commit 5c5866c593bb don't really introduce any problem but happened
 to make the issue more explicit and it's easier to get a panic. :) 

> > Signed-off-by: Zeng Tao <prime.zeng@hisilicon.com>
> > ---
> >  drivers/vfio/pci/vfio_pci.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index f634c81..de881a6 100644
> > --- a/drivers/vfio/pci/vfio_pci.c
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -521,14 +521,19 @@ static void vfio_pci_release(void
> *device_data)
> >  		vfio_pci_vf_token_user_add(vdev, -1);
> >  		vfio_spapr_pci_eeh_release(vdev->pdev);
> >  		vfio_pci_disable(vdev);
> > +		mutex_lock(&vdev->igate);
> >  		if (vdev->err_trigger) {
> >  			eventfd_ctx_put(vdev->err_trigger);
> >  			vdev->err_trigger = NULL;
> >  		}
> > +		mutex_unlock(&vdev->igate);
> > +
> > +		mutex_lock(&vdev->igate);
> 
> Just keep the mutex locked for both triggers?
two reasons here:
1.  Just keep a smaller lock, it's a better practice. 
2.  Let the pending request to finish if there is race condition.

> 
> >  		if (vdev->req_trigger) {
> >  			eventfd_ctx_put(vdev->req_trigger);
> >  			vdev->req_trigger = NULL;
> >  		}
> > +		mutex_unlock(&vdev->igate);
> >  	}
> >
> >  	mutex_unlock(&vdev->reflck->lock);