On Fri, Apr 1, 2011 at 7:34 AM, Robert ÅwiÄcki <robert@xxxxxxxxxxx> wrote: > > Hey, I'll apply your patch and check it out. In the meantime I > triggered another Oops (NULL-ptr deref via sys_mprotect). > > The oops is here: > > http://alt.swiecki.net/linux_kernel/sys_mprotect-2.6.38.txt That's not a NULL pointer dereference. That's a BUG_ON(). And for some reason you've turned off the BUG_ON() messages, saving some tiny amount of memory. Anyway, it looks like the first BUG_ON() in vma_prio_tree_add(), so it would be this one: BUG_ON(RADIX_INDEX(vma) != RADIX_INDEX(old)); but it is possible that gcc has shuffled things around (so it _might_ be the HEAP_INDEX() one). If you had CONFIG_DEBUG_BUGVERBOSE=y, you'd get a filename and line number. One reason I hate -O2 in cases like this is that the basic block movement makes it way harder to actually debug things. I would suggest using -Os too (CONFIG_OPTIMIZE_FOR_SIZE or whatever it's called). Anyway, I do find it worrying. The vma code shouldn't be this fragile. Hugh? I do wonder what triggers this. Is it a huge-page vma? We seem to be lacking the check to see that mprotect() is on a hugepage boundary - and that seems bogus. Or am I missing some check? The new transparent hugepage support splits the page, but what if it's a _static_ hugepage thing? But why would that affect the radix_index thing? I have no idea. I'd like to blame the anon_vma rewrites last year, but I can't see why that should matter either. Again, hugepages had some special rules, I think (and that would explain why nobody normal sees this). Guys, please give this one a look. Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href