Re: 2.6.17-rc5-mm1

[Hugh Dickins]

On Tue, 6 Jun 2006, Christoph Lameter wrote:
> 
> Would it not be better for an arch to explicitly tell us how many swap 
> devices are supported? Then we could make the swap_info array shorter and 
> get rid of this cryptic test.

If they differed at all, yes.

> This test also creates a problem for the migration entries: It is really 
> not clear until runtime how many swap devices are supported so we cannot 
> take the last 2 for page migration. In order for page migration to work 
> all NUMA arches that do not support 32 swap devices need to define 
> CONFIG_MIGRATION=n. Seems that this is only s390?

Even s390 is okay, isn't it?  MartinS's swp_type returns the highest
type, 31, corresponding to 32 types, as on every other architecture.
You and I and Martin Bligh would prefer this patch...


Remove unnecessary obfuscation from sys_swapon's range check on swap
type, which blew up causing memory corruption once swapless migration
made MAX_SWAPFILES no longer 2 ^ MAX_SWAPFILES_SHIFT.

Signed-off-by: Hugh Dickins <hugh@xxxxxxxxxxx>

--- 2.6.17-rc5-mm3/mm/swapfile.c	2006-06-04 11:52:47.000000000 +0100
+++ linux/mm/swapfile.c	2006-06-06 18:53:40.000000000 +0100
@@ -1404,7 +1404,7 @@ asmlinkage long sys_swapon(const char __
 	 * from the initial ~0UL that can't be encoded in either the
 	 * swp_entry_t or the architecture definition of a swap pte.
 	 */
-	if (type > swp_type(pte_to_swp_entry(swp_entry_to_pte(swp_entry(~0UL,0))))) {
+	if (type >= MAX_SWAPFILES) {
 		spin_unlock(&swap_lock);
 		goto out;
 	}
-
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