Messages in this thread | | | From | Bjorn Helgaas <> | Subject | Re: [PATCH] avoiding the same resource to be inserted | Date | Wed, 25 Aug 2010 09:17:52 -0600 |
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On Tuesday, August 24, 2010 10:31:52 pm Huang Shijie wrote: > On Wed, Aug 25, 2010 at 7:46 AM, Andrew Morton > <akpm@linux-foundation.org> wrote: > > On Mon, 16 Aug 2010 23:55:38 +0800 > > Huang Shijie <shijie8@gmail.com> wrote: > > > >> If the same resource is inserted to the resource tree > >> (maybe not on purpose), a dead loop will be created. In this situation, > >> The kernel does not report any warning or error :( > >> > >> The command below will show a endless print. > >> #cat /proc/iomem > > > > OK, we shouldn't do that. > > > >> So, adding the check for the same resource is needed for the stability > >> and reliability of the kernel. > >> > >> Signed-off-by: Huang Shijie <shijie8@gmail.com> > >> --- > >> kernel/resource.c | 2 +- > >> 1 files changed, 1 insertions(+), 1 deletions(-) > >> > >> diff --git a/kernel/resource.c b/kernel/resource.c > >> index 7b36976..60daab4 100644 > >> --- a/kernel/resource.c > >> +++ b/kernel/resource.c > >> @@ -451,7 +451,7 @@ static struct resource * __insert_resource(struct resource *parent, struct resou > >> if (!first) > >> return first; > >> > >> - if (first == parent) > >> + if (first == parent || first == new) > >> return first; > > > > However, inserting the same thing twice _is_ a bug, and we shouldn't > > silently accept it like this. We should tell the programmer! > > Indeed, this is a bug caused by the driver programmer.I had spent > nearly two day to find it in my colleague's code.
insert_resource() is a hack to deal with the fact that we don't discover resources in the logical order, so sometimes we have to go back and add a resource after we've already added "children" of the new resource.
In my opinion, the ugliness of using insert_resource() should be confined to core architecture code, and drivers shouldn't use it at all.
That said, I think it's a good idea to add the WARN_ON().
In fact, I wonder if we should also "WARN_ON(first == parent)".
Bjorn
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