From: Mark Fortescue <mark@xxxxxxxxxxxxxxxxxx> Date: Tue, 31 Jul 2007 08:55:20 +0100 (BST) > I have formulated a patch that prevents the update_mmu_cache from doing > enything if there is no context available. This apears to have no > immediate, undesirable side effects. > > This worked better than the alternative of setting up a context to work with. > > Can you for see any issues in doing this? > > If not, can you check+apply the attached (un-mangled) patch. Thanks for tracking this down Mark. The issue is that, when exec()'ing to userspace from a kernel thread, we need activate_context() to be invoked before we try to touch userspace at all. This new argument handling is invoking get_user_pages() before that happens. activate_context() happens via flush_old_exec(), but that occurs via load_elf_binary() et al. which is long after the argument fetching code runs in fs/exec.c that is using get_user_pages(). (Mark, hint: activate_context() is defined to switch_mm() on sparc32, which is sun4c_switch_mm() which you thought was only invoked from context switches :-)) Touching userspace before activate_context() is questionable at best, in my opinion. But I can't come up with a good way to fix this right now other than Mark's sparc patch, so I will apply it. Thanks again Mark! - To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
