* Oleg Nesterov <[email protected]> [2012-07-09 12:09:20]: > On 07/09, Peter Zijlstra wrote: > > > > On Sun, 2012-07-08 at 22:30 +0200, Oleg Nesterov wrote: > > > uprobe_munmap() does get_user_pages() and it is also called from > > > the final mmput()->exit_mmap() path. This slows down exit/mmput() > > > for no reason, and I think it is simply dangerous/wrong to try to > > > fault-in a page into the dying mm. If nothing else, this happens > > > after the last sync_mm_rss(), afaics handle_mm_fault() can change > > > the task->rss_stat and make the subsequent check_mm() unhappy. > > > > > > Change uprobe_munmap() to check mm->mm_users != 0. > > > > > > Signed-off-by: Oleg Nesterov <[email protected]> > > > --- > > > kernel/events/uprobes.c | 3 +++ > > > 1 files changed, 3 insertions(+), 0 deletions(-) > > > > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > > > index a93b6df..47c4e24 100644 > > > --- a/kernel/events/uprobes.c > > > +++ b/kernel/events/uprobes.c > > > @@ -1082,6 +1082,9 @@ void uprobe_munmap(struct vm_area_struct *vma, > > > unsigned long start, unsigned lon > > > if (!atomic_read(&uprobe_events) || !valid_vma(vma, false)) > > > return; > > > > > > + if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */ > > > + return; > > > + > > > if (!atomic_read(&vma->vm_mm->uprobes_state.count)) > > > return; > > > > > > > But won't you leak uprobe refcounts like this? Those aren't tied to the > > task (which is dying) but to the vma's mapping the appropriate hunk of > > the text. Not doing the munmap will then not put the uprobe->ref.. > > No, mmap/munmap do not participate in uprobe refcounting. This code > does put_uprobe() for each uprobe, yes, but only because the counter > was incremented in build_probe_list(). >
Right -- Thanks and Regards Srikar -- 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/
