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Date:   Sat, 19 Mar 2022 16:59:28 +0100
From:   Andrea Parri <parri.andrea@gmail.com>
To:     Saurabh Singh Sengar <ssengar@microsoft.com>
Cc:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        Wei Hu <weh@microsoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Rob Herring <robh@kernel.org>,
        Krzysztof Wilczynski <kw@linux.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [EXTERNAL] [PATCH 1/2] PCI: hv: Use IDR to generate transaction
 IDs for VMBus hardening
Message-ID: <20220319155928.GA2951@anparri>
References: <20220318174848.290621-1-parri.andrea@gmail.com>
 <20220318174848.290621-2-parri.andrea@gmail.com>
 <KL1P15301MB0295879FF28B67F3C521FFB3BE149@KL1P15301MB0295.APCP153.PROD.OUTLOOK.COM>
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> > @@ -1208,6 +1211,27 @@ static void hv_pci_read_config_compl(void
> > *context, struct pci_response *resp,
> >  	complete(&comp->comp_pkt.host_event);
> >  }
> > 
> > +static inline int alloc_request_id(struct hv_pcibus_device *hbus,
> > +				   void *ptr, gfp_t gfp)
> > +{
> > +	unsigned long flags;
> > +	int req_id;
> > +
> > +	spin_lock_irqsave(&hbus->idr_lock, flags);
> > +	req_id = idr_alloc(&hbus->idr, ptr, 1, 0, gfp);
> 
> [Saurabh Singh Sengar] Many a place we are using alloc_request_id with GFP_KERNEL, which results this allocation inside of spin lock with GFP_KERNEL.

That's a bug.


> Is this a good opportunity to use idr_preload ?

I'd rather fix (and 'simplify' a bit the interface) by doing:

static inline int alloc_request_id(struct hv_pcibus_device *hbus, void *ptr)
{
	unsigned long flags;
	int req_id;

	spin_lock_irqsave(&hbus->idr_lock, flags);
	req_id = idr_alloc(&hbus->idr, ptr, 1, 0, GFP_ATOMIC);
	spin_unlock_irqrestore(&hbus->idr_lock, flags);
	return req_id;
}

Thoughts?

Thanks,
  Andrea