Windows System Software -- Consulting, Training, Development -- Unique Expertise, Guaranteed Results

Home› NTDEV
Before Posting...
Please check out the Community Guidelines in the Announcements and Administration Category.

More Info on Driver Writing and Debugging


The free OSR Learning Library has more than 50 articles on a wide variety of topics about writing and debugging device drivers and Minifilters. From introductory level to advanced. All the articles have been recently reviewed and updated, and are written using the clear and definitive style you've come to expect from OSR over the years.


Check out The OSR Learning Library at: https://www.osr.com/osr-learning-library/


WorkItem SynchronizationScope / AutomaticSerialization

msrmsr Member Posts: 351
in NTDEV

Hi

I have below inherited code that creates syncScope/AutoSerialization (w.r.t workItem).

  • It creates a Queue object to limit SyncScope of the WorkItem.
  • During Queue creation it chooses WdfExecutionLevelPassive/WdfSynchronizationScopeQueue. ,
    (parent of queue is WDFDEVICE and WDFDEVICE doesn't change any of its defaults i..e WdfSynchronizationScopeInheritFromParent(= none), WdfExecutionLevelInheritFromParent (=dispatch))

I have below questions as to what Fx does with below settings
1. Is the WorkItem serialized against anything in driver (those callbacks which have AutomaticSerialization = TRUE (and ExecutionLevelPassive)); ? Not sure
2. Is the workItem serialized against itself ? YES?

Thanks

    //queue
    WDF_IO_QUEUE_CONFIG_INIT(&queueConfig, WdfIoQueueDispatchManual);
    queueConfig.PowerManaged = WdfFalse;

   WDF_OBJECT_ATTRIBUTES attributes;
    attributes.ParentObject = Device;
    attributes.ExecutionLevel = WdfExecutionLevelPassive;
    attributes.SynchronizationScope = WdfSynchronizationScopeQueue;

    WDFQUEUE ParentObjectWdfQueue = NULL;
    NTSTATUS status = WdfIoQueueCreate(Device, &queueConfig, &attributes, &ParentObjectWdfQueue);

--Workitem
    WDF_WORKITEM_CONFIG_INIT(&workitemConfig, func);
    NT_ASSERT(workitemConfig.AutomaticSerialization == TRUE);

    // Set the parent object to be device
    WDF_OBJECT_ATTRIBUTES_INIT_CONTEXT_TYPE(&attributes, WORKITEM_CONTEXT);
    attributes.ParentObject = ParentObjectWdfQueue; //parent is queue, parent of queue is device

    NTSTATUS status = WdfWorkItemCreate(&workitemConfig, &attributes, t);
· Share on Facebook

Comments

  • Peter_Viscarola_(OSR)Peter_Viscarola_(OSR) Administrator Posts: 8,240

    In your code, the work item is serialized against all other things protected by Sync Scope Queue (so, for example, the EvtIoXxx Event Processing Callbacks at the Queue level).

    In general, specifying Sync Scope is not a best practice.

    Peter

    Peter Viscarola
    OSR
    @OSRDrivers

    · Share on Facebook
  • msrmsr Member Posts: 351

    Thanks Peter.

    In above, a specific Queue is created for specific purpose to parent each WORKITEM.
    (Also these queues have no EvtIoXXX() calls associated with them (at least explicitly within the driver))

    i.e. WDFWORKITEM-1 parented by WDFQUEUE-1 and WDFWORKITEM-2 parented by WDFQUEUE-2.
    (Each WDFWORKITEM has default AutomaticSerialization=TRUE)

    So can I assume below

    • Even though each WORKITEM has syncScope Queue, since the parent of each WDFWORKITEM is a distinct queue, WORKITEM-1 isn't synched with WORKITEM-2 even though they have AutomaticSerialization set to true?

    Thanks

    · Share on Facebook
  • Tim_RobertsTim_Roberts Member - All Emails Posts: 13,768

    If you use AutomaticSerialization, then ISRs, DPCs, work items, and timers are all serialized.

    I want to emphasize what Peter said. As a general rule, AutomaticSerialization and Sync Scope are bad ideas. They are a bandaid to cover up lazy coding, and they can very easily lead to deadlocks.

    Do your job as an engineer. Figure out what parts of your state need protecting, and add locks where those items are updated. Turn off the automatic locking. Your system will run better because of it.

    Tim Roberts, [email protected]
    Providenza & Boekelheide, Inc.

    · Share on Facebook
  • Peter_Viscarola_(OSR)Peter_Viscarola_(OSR) Administrator Posts: 8,240

    If you use AutomaticSerialization, then ISRs, DPCs, work items, and timers are all serialized.

    Actually, not quite correct. Your ISR is never serialized by this, and your timers, DPCs, and work items are only serialized if you set the AutomaticSerialization field for those structures to TRUE.

    Sync Scope was not a good idea when it was created, and it’s use is rarely a good idea now. The idea was to further simplify driver writing... the result was to create more locking that people who don’t understand locking still don’t understand.

    Peter

    Peter Viscarola
    OSR
    @OSRDrivers

    · Share on Facebook
  • NtDev_GeekNtDev_Geek Member - All Emails Posts: 114

    Read this beautiful article by none other than OSR only.
    https://www.osr.com/nt-insider/2014-issue3/understanding-sync-scope-wdf-drivers/

    · Share on Facebook
Sign In or Register to comment.

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Sign In Register
Upcoming OSR Seminars
OSR has suspended in-person seminars due to the Covid-19 outbreak. But, don't miss your training! Attend via the internet instead!
Writing WDF Drivers 7 Dec 2020 LIVE ONLINE
Internals & Software Drivers 25 Jan 2021 LIVE ONLINE
Developing Minifilters 8 March 2021 LIVE ONLINE

Categories