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

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Message-Id: <20210408220440.aab59f2f06beb840c22377b3@linux-foundation.org>
Date:   Thu, 8 Apr 2021 22:04:40 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Daniel Colascione <dancol@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Joe Perches <joe@...ches.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Peter Xu <peterx@...hat.com>, Shaohua Li <shli@...com>,
        Shuah Khan <shuah@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Wang Qing <wangqing@...o.com>, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        Brian Geffon <bgeffon@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH 0/9] userfaultfd: add minor fault handling for shmem

On Thu,  8 Apr 2021 16:43:18 -0700 Axel Rasmussen <axelrasmussen@...gle.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.