Re: [linux-pm] [PATCH] Threads shouldn't inherit PF_NOFREEZE

[Nigel Cunningham]

Hi Alan.

On Wed, 2005-10-19 at 05:29, Alan Stern wrote:
> The PF_NOFREEZE process flag should not be inherited when a thread is 
> forked.  This patch (as585) removes the flag from the child.
> 
> This problem is starting to show up more and more as drivers turn to the
> kthread API instead of using kernel_thread().  As a result, their kernel
> threads are now children of the kthread worker instead of modprobe, and
> they inherit the PF_NOFREEZE flag.  This can cause problems during system
> suspend; the kernel threads are not getting frozen as they ought to be.
> 
> Alan Stern

I have this in kthread instead, so that multithreaded userspace
processes only need to have NOFREEZE set once (before forking). Yes, I
have one that fits this scenario - I'm working on a userspace storage
maanger, which will setup and tear down a network connection at
appropriate times during a suspend-to-disk cycle. The initial version is
based on nbd and uses two threads because the one that sets up storage
blocks in a syscall as Pavel & others have written it.

Anyway, I agree that the general need you're trying to address is real.

Regards,

Nigel

> 
> 
> Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> 
> ---
> 
> What I said above may not be quite true.  For all I know, there may be
> threads which rely on inheriting PF_NOFREEZE from their parent.  But it
> should not be inherited by default.
> 
> Index: usb-2.6/kernel/fork.c
> ===================================================================
> --- usb-2.6.orig/kernel/fork.c
> +++ usb-2.6/kernel/fork.c
> @@ -848,7 +848,7 @@ static inline void copy_flags(unsigned l
>  {
>  	unsigned long new_flags = p->flags;
>  
> -	new_flags &= ~PF_SUPERPRIV;
> +	new_flags &= ~(PF_SUPERPRIV | PF_NOFREEZE);
>  	new_flags |= PF_FORKNOEXEC;
>  	if (!(clone_flags & CLONE_PTRACE))
>  		p->ptrace = 0;
> 
> 
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