linux-kernel - Re: [PATCH 1/3] selftests: vm: add process

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Date:   Tue, 10 May 2022 09:42:32 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Minchan Kim <minchan@...nel.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jann Horn <jannh@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        John Hubbard <jhubbard@...dia.com>, shuah@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, linux-kselftest@...r.kernel.org,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/3] selftests: vm: add process_mrelease tests

On Tue, May 10, 2022 at 9:36 AM Shuah Khan <skhan@...uxfoundation.org> wrote:
>
> On 5/10/22 10:29 AM, Suren Baghdasaryan wrote:
> > On Tue, May 10, 2022 at 8:43 AM Shuah Khan <skhan@...uxfoundation.org> wrote:
> >>
> >> On 5/9/22 9:00 PM, Suren Baghdasaryan wrote:
> >>> Introduce process_mrelease syscall sanity tests. They include tests of
> >>> invalid pidfd and flags inputs, attempting to call process_mrelease
> >>> with a live process and a valid usage of process_mrelease. Because
> >>> process_mrelease has to be used against a process with a pending SIGKILL,
> >>> it's possible that the process exits before process_mrelease gets called.
> >>> In such cases we retry the test with a victim that allocates twice more
> >>> memory up to 1GB. This would require the victim process to spend more
> >>> time during exit and process_mrelease has a better chance of catching
> >>> the process before it exits.
> >>>
> >>
> >> +1 on Mike's comments on improving the change log. List what is getting
> >> tested as opposed to describing the test code.
> >
> > I'll try to improve the description but IMHO it does describe what
> > it's testing - the process_mrelease syscall with valid and invalid
> > inputs. I could omit the implementation details if that helps.
> >
> >>
> >>> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> >>> ---
> >>>    tools/testing/selftests/vm/Makefile        |   1 +
> >>>    tools/testing/selftests/vm/mrelease_test.c | 176 +++++++++++++++++++++
> >>>    tools/testing/selftests/vm/run_vmtests.sh  |  16 ++
> >>>    3 files changed, 193 insertions(+)
> >>>    create mode 100644 tools/testing/selftests/vm/mrelease_test.c
> >>
> >> Please update .gitignore with the new executable.
> >
> > Ack.
> >
> >>
> >>>
> >>> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> >>> index 04a49e876a46..733fccbff0ef 100644
> >>> --- a/tools/testing/selftests/vm/Makefile
> >>> +++ b/tools/testing/selftests/vm/Makefile
> >>> @@ -43,6 +43,7 @@ TEST_GEN_FILES += map_populate
> >>>    TEST_GEN_FILES += memfd_secret
> >>>    TEST_GEN_FILES += mlock-random-test
> >>>    TEST_GEN_FILES += mlock2-tests
> >>> +TEST_GEN_FILES += mrelease_test
> >>>    TEST_GEN_FILES += mremap_dontunmap
> >>>    TEST_GEN_FILES += mremap_test
> >>>    TEST_GEN_FILES += on-fault-limit
> >>> diff --git a/tools/testing/selftests/vm/mrelease_test.c b/tools/testing/selftests/vm/mrelease_test.c
> >>> new file mode 100644
> >>> index 000000000000..a61061bf8433
> >>> --- /dev/null
> >>> +++ b/tools/testing/selftests/vm/mrelease_test.c
> >>> @@ -0,0 +1,176 @@
> >>> +// SPDX-License-Identifier: GPL-2.0
> >>> +/*
> >>> + * Copyright 2022 Google LLC
> >>> + */
> >>> +#define _GNU_SOURCE
> >>> +#include <errno.h>
> >>> +#include <stdio.h>
> >>> +#include <stdlib.h>
> >>> +#include <sys/wait.h>
> >>> +#include <unistd.h>
> >>> +
> >>> +#include "util.h"
> >>> +
> >>> +static inline int pidfd_open(pid_t pid, unsigned int flags)
> >>> +{
> >>> +#ifdef __NR_pidfd_open
> >>> +     return syscall(__NR_pidfd_open, pid, flags);
> >>> +#else
> >>> +     errno = ENOSYS;
> >>
> >> This isn't an error - this would be skip because this syscall
> >> isn't supported.
> >
> > Ack.
> >
> >>
> >>> +     return -1;
> >>> +#endif
> >>
> >> Key off of syscall return instead of these ifdefs - same comment
> >> on all of the ifdefs
> >
> > Ack. I was using some other test as an example but I guess that was
> > not a good model.
> >
> >>
> >>> +}
> >>> +
> >>
> >> I am not seeing any reason for breaking this code up have a separate
> >> routine for pidfd_open().
> >
> > I'm a bit unclear what you mean. Do you mean that userspace headers
> > should already define pidfd_open() and I don't need to define it?
> >
>
> Do you need pidfd_open() or can this be part of main? Without the ifdefs,
> it is really a one line code.

Ah, I see. I think it's cleaner that way but I'll make them one-line
inline functions.

>
> thanks,
> -- Shuah