Messages in this thread | | | Date | Mon, 9 Jul 2012 15:55:59 +0530 | From | Srikar Dronamraju <> | Subject | Re: [PATCH 2/5] uprobes: suppress uprobe_munmap() from mmput() |
| |
* Oleg Nesterov <oleg@redhat.com> [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 <oleg@redhat.com> > > > --- > > > 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
| |