Subject: Re: [PATCH 03/29] mm: allow PF_MEMALLOC from softirq context

From: Peter Zijlstra <[email-masked]>
Date: Thu, 22 Feb 2007 10:16:23 +0100

On Wed, 2007-02-21 at 16:53 +0100, Arjan van de Ven wrote:
> > Index: linux-2.6-git/kernel/softirq.c
> > ===================================================================
> > --- linux-2.6-git.orig/kernel/softirq.c	2006-12-14 10:02:18.000000000 +0100
> > +++ linux-2.6-git/kernel/softirq.c	2006-12-14 10:02:52.000000000 +0100
> > @@ -209,6 +209,8 @@ asmlinkage void __do_softirq(void)
> >  	__u32 pending;
> >  	int max_restart = MAX_SOFTIRQ_RESTART;
> >  	int cpu;
> > +	unsigned long pflags = current->flags;
> > +	current->flags &= ~PF_MEMALLOC;
> >  
> >  	pending = local_softirq_pending();
> >  	account_system_vtime(current);
> > @@ -247,6 +249,7 @@ restart:
> >  
> >  	account_system_vtime(current);
> >  	_local_bh_enable();
> > +	current->flags = pflags;
> 
> this wipes out all the flags in one go.... evil.
> What if something just selected this process for OOM killing? you nuke
> that flag here again. Would be nicer if only the PF_MEMALLOC bit got
> inherited in the restore path..

would something like this:

#define PF_PUSH(tsk, pflags, mask)		\
do {						\
	(pflags) = ((tsk)->flags) & (mask);	\
} while (0)

#define PF_POP(tsk, pflags, mask)		\
do {						\
	((tsk)->flags &= ~(mask);		\
	((tsk)->flags |= (pflags);		\
} while (0)

be useful, or shall I just open code it in various places?

(I made this same mistake; ignorant of the problem; all over this patch series)