linux-kernel - Re: [PATCH] resource: make sure requested range intersects root range

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Date:	Thu, 12 Jul 2012 16:56:31 +0800
From:	Ram Pai <linuxram@...ibm.com>
To:	Ram Pai <linuxram@...ibm.com>
Cc:	"Purdila, Octavian" <octavian.purdila@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH] resource: make sure requested range intersects root range

On Thu, Jul 12, 2012 at 10:02:06AM +0800, Ram Pai wrote:
> On Wed, Jul 11, 2012 at 06:26:49PM +0300, Purdila, Octavian wrote:
> > On Wed, Jul 11, 2012 at 5:54 PM, Ram Pai <linuxram@...ibm.com> wrote:
> > > On Wed, Jul 11, 2012 at 02:06:10PM +0300, Purdila, Octavian wrote:
> > >> On Wed, Jul 11, 2012 at 5:09 AM, Ram Pai <linuxram@...ibm.com> wrote:
> > >>
> > >> >
> > >> > Wait.. I am not sure this will fix the problem entirely. The above check
> > >> > will handle the case where the range requested is entirey out of the
> > >> > root's range.  But if the requested range overlapps that of the root
> > >> > range, we will still call __reserve_region_with_split() and end up with
> > >> > a recursion if there is a overflow. Wont we?
> > >> >
> > >>
> > >> Good catch. I will fix this as well as address Andrew's and Joe's
> > >> comments in a new patch. The only question is how to handle the
> > >> overlap case:
> > >>
> > >> (a) abort the whole request or
> > >>
> > >> (b) try to reserve the part that overlaps (and adjust the request to
> > >> avoid the overflow)
> > >>
> > >> I think (b) is more in line with the current implementation for reservations.
> > >
> > >
> > > I prefer (b).  following patch should handle that.
> > >
> > > diff --git a/kernel/resource.c b/kernel/resource.c
> > > index e1d2b8e..dd87fde 100644
> > > --- a/kernel/resource.c
> > > +++ b/kernel/resource.c
> > > @@ -780,6 +780,10 @@ static void __init __reserve_region_with_split(struct resource *root,
> > >
> > >         if (conflict->start > start)
> > >                 __reserve_region_with_split(root, start, conflict->start-1, name);
> > > +
> > > +       if (conflict->end == parent->end )
> > > +               return;
> > > +
> > >         if (conflict->end < end)
> > >                 __reserve_region_with_split(root, conflict->end+1, end, name);
> > >  }
> > >
> > 
> > I don't think this covers all cases, e.g. if root range starts
> > somewhere above 0 and the request is below the root start point.
> 

Ok. I see your point.  Here is a proposal that incoporates the best of all 
the proposals till now..


diff --git a/kernel/resource.c b/kernel/resource.c
index e1d2b8e..c6f4958 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -789,7 +789,19 @@ void __init reserve_region_with_split(struct resource *root,
 		const char *name)
 {
 	write_lock(&resource_lock);
-	__reserve_region_with_split(root, start, end, name);
+	if (start > root->end || end < root->start) {
+ 		pr_err("Requested range (0x%llx-0x%llx) not in root range (0x%llx-0x%llx)\n",
+ 		       (unsigned long long)start, (unsigned long long)end,
+ 		       (unsigned long long)root->start,
+ 		       (unsigned long long)root->end);
+		dump_stack();
+	} else {
+		if (start < root->start)
+			start = root->start;
+		if (end > root->end)
+			end = root->end;
+ 		__reserve_region_with_split(root, start, end, name);
+	}
 	write_unlock(&resource_lock);
 }
 

Offcourse; it does not warn when the request is partially out of root's range.
But that should be ok, because its still a valid request.
RP

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