Re: [ros-dev] [ros-diffs] [gedmurphy] 70408: [NTOSKRNL] - Raise the IRQL when enumerating device lists so it doesn't get edited mid-listing - Don't hardcode the pointer size when checking the buffer size

[Thomas Faber]

I think this might be an SP/MP difference?
Would make sense if KeAcquireSpinLock inside an SP kernel becomes
KeRaiseIrql. But even for a 2003 MP kernel this would serve no purpose.

On 2015-12-29 21:48, Ged Murphy wrote:
> It depends on whether we want to emulate the 2k3 kernel or not.
>
> I noticed in my 2k3 fltmgr testing that IoEnumerateDeviceObjectList runs at
> DPC for the entirety of the function. This was changed in the NT6 kernel to
> use a lock, which is indeed the LockQueueIoDatabaseLock Hermes mentioned.
>
> I'm happy to use the spinlock (and would prefer to myself), but any move
> towards NT6 normally results in an angry email, so I opted for the 2k3
> approach  ;)
>
> Ged.
>
> -----Original Message-----
> From: Ros-dev [mailto:[e-mail]] On Behalf Of Hermès
> BÉLUSCA - MAÏTO
> Sent: 29 December 2015 16:08
> To: 'ReactOS Development List' [e-mail]
> Subject: Re: [ros-dev] [ros-diffs] [gedmurphy] 70408: [NTOSKRNL] - Raise the
> IRQL when enumerating device lists so it doesn't get edited mid-listing -
> Don't hardcode the pointer size when checking the buffer size
>
> Yes this should be a spinlock involved instead, for example the
> "LockQueueIoDatabaseLock" (queued) spinlock that we already use in other
> places in the code.
>
> -----Message d'origine-----
> De : Ros-dev [mailto:[e-mail]] De la part de Thomas Faber
> Envoyé : mardi 29 décembre 2015 13:20 À : [e-mail] Objet : Re:
> [ros-dev] [ros-diffs] [gedmurphy] 70408: [NTOSKRNL] - Raise the IRQL when
> enumerating device lists so it doesn't get edited mid-listing - Don't
> hardcode the pointer size when checking the buffer size
>
> Uhm... raising the IRQL is not a synchronization mechanism. Should there be
> a spinlock involved?
>
> On 2015-12-23 12:26, [e-mail] wrote:
> > Author: gedmurphy
> > Date: Wed Dec 23 11:26:28 2015
> > New Revision: 70408
> >
> > URL: http://svn.reactos.org/svn/reactos?rev=70408&view=rev
> > Log:
> > [NTOSKRNL]
> > Raise the IRQL when enumerating device lists so it doesn't get
> >
> > edited mid-listing
> > Don't hardcode the pointer size when checking the buffer size
> >
> > Modified:
> >     trunk/reactos/ntoskrnl/io/iomgr/device.c
> >
> > Modified: trunk/reactos/ntoskrnl/io/iomgr/device.c
> > URL: 
> > http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/io/iomgr/dev
> > ice.c?rev=70408&r1=70407&r2=70408&view=diff
> ============================================================================
> > --- trunk/reactos/ntoskrnl/io/iomgr/device.c	[iso-8859-1] (original)
> > +++ trunk/reactos/ntoskrnl/io/iomgr/device.c	[iso-8859-1] Wed Dec 23
>
> 11:26:28 2015
> > @@ -1088,6 +1088,10 @@
> >  {
> >      ULONG ActualDevices = 1;
> >      PDEVICE_OBJECT CurrentDevice = DriverObject->DeviceObject;
> >
> > KIRQL OldIrql;
> >
> > /* Raise to dispatch level */
> >
> > KeRaiseIrql(DISPATCH_LEVEL, &OldIrql);
> >
> > /* Find out how many devices we'll enumerate */
> > while ((CurrentDevice = CurrentDevice->NextDevice))
> >
> > ActualDevices++; @@ -1099,13 +1103,14 @@
> >      *ActualNumberDeviceObjects = ActualDevices;
> >  /* Check if we can support so many */
> > if ((ActualDevices * 4) > DeviceObjectListSize)
> > if ((ActualDevices * sizeof(PDEVICE_OBJECT)) >
> > DeviceObjectListSize)
> >    {
> >        /* Fail because the buffer was too small */
> >    KeLowerIrql(OldIrql);
> >    return STATUS_BUFFER_TOO_SMALL;
> > }
> > /* Check if the caller only wanted the size */
> >
> > /* Check if the caller wanted the device list */
> > if (DeviceObjectList)
> > {
> >     /* Loop through all the devices */ @@ -1123,6 +1128,9 @@
> >         DeviceObjectList++;
> >     }
> > }
> >
> > /* Return back to previous IRQL */
> >
> > KeLowerIrql(OldIrql);
> >
> > /* Return the status */
> > return STATUS_SUCCESS;