On Wed, Oct 17, 2007 at 01:36:51PM +0200, Bernhard Walle wrote:
[..]
> > > +static int __init reserve_bootmem_core(bootmem_data_t *bdata, unsigned long addr,
> > > + unsigned long size, int flags)
> > > {
> > > unsigned long sidx, eidx;
> > > unsigned long i;
> > > @@ -133,7 +133,11 @@ static void __init reserve_bootmem_core(
> > > #ifdef CONFIG_DEBUG_BOOTMEM
> > > printk("hm, page %08lx reserved twice.\n", i*PAGE_SIZE);
> > > #endif
> > > + if (flags & BOOTMEM_EXCLUSIVE)
> > > + return -EBUSY;
> >
> > I think we should unreserve the chunks of memory we have reserved so
> > far (Memory reserved from sidx to i), in case of error.
>
> Unfortunately, that's not possible without using a lock (or counters
> instead of a bitmap) any more. If we just do
>
> for (i--; i >= sidx; i--)
> clear_bit(i, bdata->node_bootmem_map);
>
> then another thread of execution could reserve the memory (without
> BOOTMEM_EXCLUSIVE) in between -- and the code would free the memory
> which is already reserved.
>
> I think that could be modelled with a rwlock, not changing the default
> case where BOOTMEM_EXCLUSIVE is not specified.
SMP initialization takes place after bootmem allocator has retired. That
would mean only one thread will be using bootmem allocator. Hence I think
unreserving memory without any kind of locking should be safe.
Thanks
Vivek
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