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From: Haiyang Zhang <haiyangz@microsoft.com>
To: Dexuan Cui <decui@microsoft.com>, "bhelgaas@google.com"
	<bhelgaas@google.com>, "wei.liu@kernel.org" <wei.liu@kernel.org>, KY
 Srinivasan <kys@microsoft.com>, "lpieralisi@kernel.org"
	<lpieralisi@kernel.org>, "linux-pci@vger.kernel.org"
	<linux-pci@vger.kernel.org>
CC: "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Boqun Feng
	<Boqun.Feng@microsoft.com>, Sunil Muthuswamy <sunilmut@microsoft.com>,
	Saurabh Singh Sengar <ssengar@microsoft.com>
Subject: RE: [PATCH] PCI: Add a mutex to protect the global list
 pci_domain_busn_res_list
Thread-Topic: [PATCH] PCI: Add a mutex to protect the global list
 pci_domain_busn_res_list
Thread-Index: AQHakfxj93z/Y5X/10y0l0FjynaRDLFvpNpg
Date: Fri, 19 Apr 2024 15:07:47 +0000
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References: <20240419015302.13871-1-decui@microsoft.com>
In-Reply-To: <20240419015302.13871-1-decui@microsoft.com>
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> -----Original Message-----
> From: Dexuan Cui <decui@microsoft.com>
> Sent: Thursday, April 18, 2024 9:53 PM
> To: bhelgaas@google.com; wei.liu@kernel.org; KY Srinivasan
> <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>;
> lpieralisi@kernel.org; linux-pci@vger.kernel.org
> Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; Boqun
> Feng <Boqun.Feng@microsoft.com>; Sunil Muthuswamy
> <sunilmut@microsoft.com>; Saurabh Singh Sengar <ssengar@microsoft.com>;
> Dexuan Cui <decui@microsoft.com>
> Subject: [PATCH] PCI: Add a mutex to protect the global list
> pci_domain_busn_res_list
>=20
> There has been an effort to make the pci-hyperv driver support
> async-probing to reduce the boot time. With async-probing, multiple
> kernel threads can be running hv_pci_probe() -> create_root_hv_pci_bus()
> ->
> pci_scan_root_bus_bridge() -> pci_bus_insert_busn_res() at the same time
> to
> update the global list, causing list corruption.
>=20
> Add a mutex to protect the list.
>=20
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
>  drivers/pci/probe.c | 25 ++++++++++++++++++-------
>  1 file changed, 18 insertions(+), 7 deletions(-)
>=20
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index e19b79821dd6..1327fd820b24 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -37,6 +37,7 @@ LIST_HEAD(pci_root_buses);
>  EXPORT_SYMBOL(pci_root_buses);
>=20
>  static LIST_HEAD(pci_domain_busn_res_list);
> +static DEFINE_MUTEX(pci_domain_busn_res_list_lock);
>=20
>  struct pci_domain_busn_res {
>  	struct list_head list;
> @@ -47,14 +48,22 @@ struct pci_domain_busn_res {
>  static struct resource *get_pci_domain_busn_res(int domain_nr)
>  {
>  	struct pci_domain_busn_res *r;
> +	struct resource *ret;
>=20
> -	list_for_each_entry(r, &pci_domain_busn_res_list, list)
> -		if (r->domain_nr =3D=3D domain_nr)
> -			return &r->res;
> +	mutex_lock(&pci_domain_busn_res_list_lock);
> +
> +	list_for_each_entry(r, &pci_domain_busn_res_list, list) {
> +		if (r->domain_nr =3D=3D domain_nr) {
> +			ret =3D &r->res;
> +			goto out;
> +		}
> +	}
>=20
>  	r =3D kzalloc(sizeof(*r), GFP_KERNEL);
> -	if (!r)
> -		return NULL;
> +	if (!r) {
> +		ret =3D NULL;
> +		goto out;
> +	}
>=20
>  	r->domain_nr =3D domain_nr;
>  	r->res.start =3D 0;
> @@ -62,8 +71,10 @@ static struct resource *get_pci_domain_busn_res(int
> domain_nr)
>  	r->res.flags =3D IORESOURCE_BUS | IORESOURCE_PCI_FIXED;
>=20
>  	list_add_tail(&r->list, &pci_domain_busn_res_list);
> -
> -	return &r->res;
> +	ret =3D &r->res;
> +out:
> +	mutex_unlock(&pci_domain_busn_res_list_lock);
> +	return ret;
>  }

The patch is for common pci code. So, this bug has been there for a while?
Do you have a sample stack trace of the crash?

I checked pci-hyperv, it doesn't define the .driver.probe_type, so=20
PROBE_DEFAULT_STRATEGY is in effect. driver_allows_async_probing() returns=
=20
false unless kernel/mod param requests async. So async probing haven't=20
been practiced here.

If in the future, we change the pci-hyperv's probe_type to PROBE_PREFER_ASY=
NCHRONOUS,=20
how does it affect the underlying PCI device's probes within the same=20
device type?
For example, MANA driver doesn't set probe_type. Will pci-hyperv's async=20
probing cause async probing or potentially nondeterministic naming for=20
MANA devices?

Thanks,
- Haiyang