On Sun, 25 Mar 2007, Thomas Gleixner wrote: > > Environment: Pre Pentium systems, (boot_cpu_data.wp_works_ok == 0)
This shouldn't be "pre-pentium", afaik. WP-works-ok on i486 too. I think only the original i386 had this bug ("feature"). But I agree, it does seem to be broken on such machines (I assume you don't actually have one, but just tested by forcing it by hand ;) > Now __copy_to_user_ll() takes the (boot_cpu_data.wp_works_ok == 0) path, > which in turn calls > > down_read(current->mm->mmap_sem) - which might sleep > > and > > get_user_pages() - which has a cond_resched() inside. > > Not sure how to fix that. I agree. Nasty. But the thing is, it's actually much worse. We use "__put_user()" earlier to try to fault it in writably, and that one is totally broken on a CPU where wp_works_ok isn't set. The whole notion that we should do this at access time is broken. We should go back to doing it at "access_ok()", or we should just state that we don't support original-i386 CPU's any more. As it is, we don't do it right *anyway*, since we only do the tests properly in __copy_to_user(), and totally miss them in __put_user() and friends. So it's buggy on i386 however you try to fix it. The only way to fix it properly is to move the i386 fixup early, into "access_ok()", the way it used to be. Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/