Re: [PATCH 0/1] s390: fix endless loop in do_signal

[Heiko Carstens <hca@linux.ibm.com>]

On Wed, Feb 15, 2023 at 02:23:20PM +0100, Greg KH wrote:
> On Wed, Feb 15, 2023 at 01:04:12PM +0100, Sumanth Korikkar wrote:
> > Hi,
> > 
> > This patch fixes the issue for s390  stable kernel starting  5.10.162.
> > The issue was specifically seen after stable version 5.10.162:
> > Following commits can trigger it:
> > 1. stable commit id - 788d0824269b ("io_uring: import 5.15-stable
> > io_uring") can trigger this problem.
> > 2. upstream commit id - 75309018a24d ("s390: add support for
> > TIF_NOTIFY_SIGNAL")
> > 
> > Problem:
> > qemu and user processes could stall when TIF_NOTIFY_SIGNAL is set from
> > io_uring work.
> > 
> > Affected users:
> > The issue was first raised by the debian team, where the s390
> > bullseye build systems are affected.
> > 
> > Upstream commit Id:
> > * The attached patch has no upstream commit. However, the stable kernel
> > 5.10.162+ uses upstream commit id - 75309018a24d ("s390: add support for
> > TIF_NOTIFY_SIGNAL"), which would need this fix
> > * Starting from v5.12, there are s390 generic entry commits 
> > 56e62a737028 ("s390: convert to generic entry")  and its relevant fixes,
> > which are recommended and should address these problems.
> 
> I'm sorry, but I do not understand.  What exact commits should be added
> to the 5.10.y tree to resolve this?

Only the patch sent by Sumanth as reply to this cover letter should be
added to the 5.10.y tree.

The problem that is addressed here is that commit 75309018a24d ("s390: add
support for TIF_NOTIFY_SIGNAL") was backported to 5.10. This commit is
broken, but nobody noticed upstream, since shortly after s390 converted to
generic entry with commit 56e62a737028 ("s390: convert to generic entry"),
which implicitly fixed that.

I doesn't look sane to backport commit 56e62a737028 ("s390: convert to
generic entry"), since that is huge and came with a lot of bugs, where I'm
not sure if all bug fixes had Fixes tags.

So the one-liner provided by Sumanth seems to be the best way to address
this bug.