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    SubjectRe: [RFC][PATCH][EXPERIMENTAL] Make kernel threads nonfreezable by default
    Date
    On Monday, 28 May 2007 12:33, Pavel Machek wrote:
    > Hi!
    >
    > > Index: linux-2.6.22-rc3/Documentation/power/kernel_threads.txt
    > > ===================================================================
    > > --- linux-2.6.22-rc3.orig/Documentation/power/kernel_threads.txt
    > > +++ linux-2.6.22-rc3/Documentation/power/kernel_threads.txt
    > > @@ -1,13 +1,22 @@
    > > -KERNEL THREADS
    > > +The Freezer and Kernel Threads
    > >
    > > -
    > > -Freezer
    > > -
    > > -Upon entering a suspended state the system will freeze all
    > > -tasks. This is done by delivering pseudosignals. This affects
    > > -kernel threads, too. To successfully freeze a kernel thread
    > > -the thread has to check for the pseudosignal and enter the
    > > -refrigerator. Code to do this looks like this:
    > > +Before entering a system-wide suspend state as well as before creating a
    > > +hibernation snapshot image the system will freeze all tasks, which is done
    > > +by delivering fake signals. This affects kernel threads too, but they won't be
    > > +frozen unless they declare that they want to. For this purpose
    >
    > Well... and unless thread that does disk writes or DMA _wants_ to, you
    > have nice disk corruption... It should be pointed out that it is not
    > voluntary for those types of threads.

    Well, that really depends.

    I think the only thing that must not be written to disk is filesystem stuff.
    The other things (eg. writing directly to block devices etc.) doesn't hurt us.

    Also, I think that DMA-ing while we're creating the image should be impossible
    due to devices being frozen at that point.

    That said, I think we need to write some better freezer documentation ASAP.

    Greetings,
    Rafael
    -
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