Messages in this thread | | | From | Axel Rasmussen <> | Date | Tue, 25 Oct 2022 11:40:39 -0700 | Subject | Re: [PATCH] userfaultfd: wake on unregister for minor faults as well as missing |
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On Tue, Oct 25, 2022 at 11:34 AM Peter Xu <peterx@redhat.com> wrote: > > On Tue, Oct 25, 2022 at 11:21:49AM -0700, Axel Rasmussen wrote: > > This was an overlooked edge case when minor faults were added. In > > general, minor faults have the same rough edge here as missing faults: > > if we unregister while there are waiting threads, they will just remain > > waiting forever, as there is no way for userspace to wake them after > > unregistration. To work around this, userspace needs to carefully wake > > everything before unregistering. > > > > So, wake for minor faults just like we already do for missing faults as > > part of the unregistration process. > > > > Cc: stable@vger.kernel.org > > Fixes: 7677f7fd8be7 ("userfaultfd: add minor fault registration mode") > > Reported-by: Lokesh Gidra <lokeshgidra@google.com> > > Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> > > --- > > fs/userfaultfd.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > > index 07c81ab3fd4d..7daee4b9481c 100644 > > --- a/fs/userfaultfd.c > > +++ b/fs/userfaultfd.c > > @@ -1606,7 +1606,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, > > start = vma->vm_start; > > vma_end = min(end, vma->vm_end); > > > > - if (userfaultfd_missing(vma)) { > > + if (userfaultfd_missing(vma) || userfaultfd_minor(vma)) { > > /* > > * Wake any concurrent pending userfault while > > * we unregister, so they will not hang > > -- > > 2.38.0.135.g90850a2211-goog > > Thanks, Axel. Is wr-protect mode also prone to this? Would a test case > help too?
I'm not quite as familiar with uffd-wp, but I think so? At minimum, it seems like waking can't *hurt*, and it would simplify the check slightly -- if (userfaultfd_armed(vma)) {}
It would also mean if we add yet another registration mode in the future, we wouldn't forget to update this.
I'll send a v2 to address both points.
> > -- > Peter Xu >
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