[PATCH] Trivial -critical : BUG()gy behaviour on OOM

[PATCH] Trivial -critical : BUG()gy behaviour on OOM

[BlaisorBlade]

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In short: in vanilla 2.6.3-rc2 (and also 2.6.2-mm1) do_swap_page() can return 
-ENOMEM while value return values are VM_FAULT_*; invalid return values can 
result in BUG() being called, so this patch (or a better fix) should go in 
soon. This patch corrects this by returning VM_FAULT_OOM in that case.

CC me on replies, please, as I'm not subscribed. Thanks.

In detail: do_swap_page returns -ENOMEM when memory allocation fails; the 
return value will in turn be returned by handle_pte_fault and handle_mm_fault 
to this code in do_page_fault:

switch (handle_mm_fault(mm, vma, address, write)) {
	case VM_FAULT_MINOR:
		tsk->min_flt++;
		break;
	case VM_FAULT_MAJOR:
		tsk->maj_flt++;
		break;
	case VM_FAULT_SIGBUS:
		goto do_sigbus;
	case VM_FAULT_OOM:
		goto out_of_memory;
	default:
		BUG();
}

So on OOM we can get a BUG. Since do_file_page does this:

         if (err == -ENOMEM)
                return VM_FAULT_OOM;

and other code shows similar behaviour, I think that the attached fix is the 
correct one.
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729

[-- Attachment #2: Fix-mm-return.patch --]
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--- ./mm/memory.c.fix	2004-02-04 20:48:15.000000000 +0100
+++ ./mm/memory.c	2004-02-14 17:59:42.000000000 +0100
@@ -1250,7 +1250,7 @@
 	mark_page_accessed(page);
 	pte_chain = pte_chain_alloc(GFP_KERNEL);
 	if (!pte_chain) {
-		ret = -ENOMEM;
+		ret = VM_FAULT_OOM;
 		goto out;
 	}
 	lock_page(page);

Re: [PATCH] Trivial -critical : BUG()gy behaviour on OOM

[William Lee Irwin III]

On Sun, Feb 15, 2004 at 04:47:39PM +0100, BlaisorBlade wrote:
> In short: in vanilla 2.6.3-rc2 (and also 2.6.2-mm1) do_swap_page() can return 
> -ENOMEM while value return values are VM_FAULT_*; invalid return values can 
> result in BUG() being called, so this patch (or a better fix) should go in 
> soon. This patch corrects this by returning VM_FAULT_OOM in that case.
> CC me on replies, please, as I'm not subscribed. Thanks.
> In detail: do_swap_page returns -ENOMEM when memory allocation fails; the 
> return value will in turn be returned by handle_pte_fault and handle_mm_fault 
> to this code in do_page_fault:

Yep. This is bust.
akpm please apply.


-- wli