Re: [RFC][PATCH][EXPERIMENTAL] Make kernel threads nonfreezable by default

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On Sunday, 27 May 2007 00:12, Rafael J. Wysocki wrote:
> Hi,
> Following the "Freezing of kernel threads" discussion
> ( I have created a patch that changes the
> freezer's behavior with respect to kernel threads.  Namely, with the patch
> applied all kernel threads are nonfreezable by default (have PF_NOFREEZE set)
> and the ones that want to be frozen need to call set_freezable() (which clears
> PF_NOFREEZE for them) and try_to_freeze().  The other (nonfreezable) kernel
> threads don't need to call try_to_freeze() any more.
> I have removed try_to_freeze() from a handful of kernel threads that I think
> need not be freezable, but in many cases I wasn't quite sure whether or not
> it was a good idea to change the current behavior.  For this reason I've added
> set_freezable() to the majority of (currently freezable) kernel threads that
> belong to device drivers and filesystems.
> Of course, I have removed the setting of PF_NOFREEZE from the kernel threads
> that are currently nonfreezable, since with the other changes in the patch it
> isn't necessary any more.
> This patch is on top of the "Freezer: Avoid freezing kernel threads prematurely"
> patch that I posted yestarday, available at
> (updated version that applies cleanly on top of 2.6.22-rc3, is available at
> It has been tested on a couple of machines and doesn't seem to break anything.
> [As you can see there are quite a lot of files affected, so I didn't add all
> maintainers of them to the CC list.  In fact, I'm not sure how to handle
> notifying them of the change, so please advise.]

Does the lack of comments mean that everyone on the CC list agrees with this
approach? ;-)

In the meantime, it turns out that this patch fixes the hibernation/suspend
problem with cryptd discussed in the thread at .

The problem is that cryptd doesn't call try_to_freeze() and doesn't set
PF_NOFREEZE for itself, so the freezer cannot handle it properly.  In principle
we can add either try_to_freeze() or the setting of PF_NOFREEZE to it, but if
the approach in the $subject patch is acceptable, we'll need to remove that
soon.  So, what should we do?


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