Re: [PATCH 0/9] userfaultfd: add minor fault handling for shmem

From: Andrew Morton <akpm@linux-foundation.org>
To: Axel Rasmussen <axelrasmussen@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Daniel Colascione <dancol@google.com>,
	Hugh Dickins <hughd@google.com>,
	Jerome Glisse <jglisse@redhat.com>, Joe Perches <joe@perches.com>,
	Lokesh Gidra <lokeshgidra@google.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Peter Xu <peterx@redhat.com>, Shaohua Li <shli@fb.com>,
	Shuah Khan <shuah@kernel.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Wang Qing <wangqing@vivo.com>,
	linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-mm@kvack.org, Brian Geffon <bgeffon@google.com>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
	Mina Almasry <almasrymina@google.com>,
	Oliver Upton <oupton@google.com>
Subject: Re: [PATCH 0/9] userfaultfd: add minor fault handling for shmem
Date: Thu, 8 Apr 2021 22:04:40 -0700	[thread overview]
Message-ID: <20210408220440.aab59f2f06beb840c22377b3@linux-foundation.org> (raw)
In-Reply-To: <20210408234327.624367-1-axelrasmussen@google.com>

On Thu,  8 Apr 2021 16:43:18 -0700 Axel Rasmussen <axelrasmussen@google.com> wrote:

> The idea is that it will apply cleanly to akpm's tree, *replacing* the following
> patches (i.e., drop these first, and then apply this series):
> 
> userfaultfd-support-minor-fault-handling-for-shmem.patch
> userfaultfd-support-minor-fault-handling-for-shmem-fix.patch
> userfaultfd-support-minor-fault-handling-for-shmem-fix-2.patch
> userfaultfd-support-minor-fault-handling-for-shmem-fix-3.patch
> userfaultfd-support-minor-fault-handling-for-shmem-fix-4.patch
> userfaultfd-selftests-use-memfd_create-for-shmem-test-type.patch
> userfaultfd-selftests-create-alias-mappings-in-the-shmem-test.patch
> userfaultfd-selftests-reinitialize-test-context-in-each-test.patch
> userfaultfd-selftests-exercise-minor-fault-handling-shmem-support.patch

Well.  the problem is,

> +	if (area_alias == MAP_FAILED)
> +		err("mmap of memfd alias failed");

`err' doesn't exist until eleventy patches later, in Peter's
"userfaultfd/selftests: unify error handling".  I got tired of (and
lost confidence in) replacing "err(...)" with "fprintf(stderr, ...);
exit(1)" everywhere then fixing up the fallout when Peter's patch came
along.  Shudder.

Sorry, all this material pretty clearly isn't going to make 5.12
(potentially nine days hence), so I shall drop all the userfaultfd
patches.  Let's take a fresh run at all of this after -rc1.

I have tentatively retained the first series:

userfaultfd-add-minor-fault-registration-mode.patch
userfaultfd-add-minor-fault-registration-mode-fix.patch
userfaultfd-disable-huge-pmd-sharing-for-minor-registered-vmas.patch
userfaultfd-hugetlbfs-only-compile-uffd-helpers-if-config-enabled.patch
userfaultfd-add-uffdio_continue-ioctl.patch
userfaultfd-update-documentation-to-describe-minor-fault-handling.patch
userfaultfd-selftests-add-test-exercising-minor-fault-handling.patch

but I don't believe they have had much testing standalone, without the
other userfaultfd patches present.  So I don't think it's smart to
upstream these in this cycle.  Or I could drop them so you and Peter
can have a clean shot at redoing the whole thing.  Please let me know.