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

From: Peter Zijlstra
Date: Thu Feb 22 2007 - 04:22:20 EST


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)

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