Re: [patch V3 01/32] mm/slab: Fix broken stack trace storage

[Thomas Gleixner]

On Sun, 14 Apr 2019, Andy Lutomirski wrote:
> > +               struct stack_trace trace = {
> > +                       .max_entries    = size - 4;
> > +                       .entries        = addr;
> > +                       .skip           = 3;
> > +               };
> 
> This looks correct, but I think that it would have been clearer if you
> left the size -= 3 above.  You're still incrementing addr, but you're
> not decrementing size, so they're out of sync and the resulting code
> is hard to follow.

What about the below?

--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1480,10 +1480,12 @@ static void store_stackinfo(struct kmem_
 	*addr++ = 0x12345678;
 	*addr++ = caller;
 	*addr++ = smp_processor_id();
+	size -= 3;
 #ifdef CONFIG_STACKTRACE
 	{
 		struct stack_trace trace = {
-			.max_entries	= size - 4;
+			/* Leave one for the end marker below */
+			.max_entries	= size - 1;
 			.entries	= addr;
 			.skip		= 3;
 		};