Re: [PATCH v7 13/14] selftests/vm: test flag is broken

[Pavel Tatashin <pasha.tatashin@soleen.com>]

On Sun, Jan 24, 2021 at 6:03 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 1/21/21 7:37 PM, Pavel Tatashin wrote:
> > In gup_test both gup_flags and test_flags use the same flags field.
> > This is broken.
> >
> > Farther, in the actual gup_test.c all the passed gup_flags are erased and
> > unconditionally replaced with FOLL_WRITE.
> >
> > Which means that test_flags are ignored, and code like this always
> > performs pin dump test:
> >
> > 155                   if (gup->flags & GUP_TEST_FLAG_DUMP_PAGES_USE_PIN)
> > 156                           nr = pin_user_pages(addr, nr, gup->flags,
> > 157                                               pages + i, NULL);
> > 158                   else
> > 159                           nr = get_user_pages(addr, nr, gup->flags,
> > 160                                               pages + i, NULL);
> > 161                   break;
> >
> > Add a new test_flags field, to allow raw gup_flags to work.
> > Add a new subcommand for DUMP_USER_PAGES_TEST to specify that pin test
> > should be performed.
> > Remove  unconditional overwriting of gup_flags via FOLL_WRITE. But,
> > preserve the previous behaviour where FOLL_WRITE was the default flag,
> > and add a new option "-W" to unset FOLL_WRITE.
> >
> > Rename flags with gup_flags.
>
> Hi Pavel,
>
> Thanks again for fixing this up! Looks good, with a tiny point about the
> subject line:
>
> 1) To follow convention, the subject line should say what you're doing,
> not what the previous condition was. Also, there are several tests in that
> directory, so we should say which one. So more like this:
>
> "selftests/vm: gup_test: fix test flag"
>
> That is just a minor documentation point, so either way, feel free to add:
>
>
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>

Thank you for your review , I will change the subject line in the next update.

Pasha

>
>
> thanks,
> --
> John Hubbard
> NVIDIA
>
> >
> > With the fix, dump works like this:
> >
> > root@virtme:/# gup_test  -c
> > ---- page #0, starting from user virt addr: 0x7f8acb9e4000
> > page:00000000d3d2ee27 refcount:2 mapcount:1 mapping:0000000000000000
> > index:0x0 pfn:0x100bcf
> > anon flags: 0x300000000080016(referenced|uptodate|lru|swapbacked)
> > raw: 0300000000080016 ffffd0e204021608 ffffd0e208df2e88 ffff8ea04243ec61
> > raw: 0000000000000000 0000000000000000 0000000200000000 0000000000000000
> > page dumped because: gup_test: dump_pages() test
> > DUMP_USER_PAGES_TEST: done
> >
> > root@virtme:/# gup_test  -c -p
> > ---- page #0, starting from user virt addr: 0x7fd19701b000
> > page:00000000baed3c7d refcount:1025 mapcount:1 mapping:0000000000000000
> > index:0x0 pfn:0x108008
> > anon flags: 0x300000000080014(uptodate|lru|swapbacked)
> > raw: 0300000000080014 ffffd0e204200188 ffffd0e205e09088 ffff8ea04243ee71
> > raw: 0000000000000000 0000000000000000 0000040100000000 0000000000000000
> > page dumped because: gup_test: dump_pages() test
> > DUMP_USER_PAGES_TEST: done
> >
> > Refcount shows the difference between pin vs no-pin case.
> > Also change type of nr from int to long, as it counts number of pages.
> >
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> > ---
> >   mm/gup_test.c                         | 23 ++++++++++-------------
> >   mm/gup_test.h                         |  3 ++-
> >   tools/testing/selftests/vm/gup_test.c | 15 +++++++++++----
> >   3 files changed, 23 insertions(+), 18 deletions(-)
> >
> > diff --git a/mm/gup_test.c b/mm/gup_test.c
> > index e3cf78e5873e..a6ed1c877679 100644
> > --- a/mm/gup_test.c
> > +++ b/mm/gup_test.c
> > @@ -94,7 +94,7 @@ static int __gup_test_ioctl(unsigned int cmd,
> >   {
> >       ktime_t start_time, end_time;
> >       unsigned long i, nr_pages, addr, next;
> > -     int nr;
> > +     long nr;
> >       struct page **pages;
> >       int ret = 0;
> >       bool needs_mmap_lock =
> > @@ -126,37 +126,34 @@ static int __gup_test_ioctl(unsigned int cmd,
> >                       nr = (next - addr) / PAGE_SIZE;
> >               }
> >
> > -             /* Filter out most gup flags: only allow a tiny subset here: */
> > -             gup->flags &= FOLL_WRITE;
> > -
> >               switch (cmd) {
> >               case GUP_FAST_BENCHMARK:
> > -                     nr = get_user_pages_fast(addr, nr, gup->flags,
> > +                     nr = get_user_pages_fast(addr, nr, gup->gup_flags,
> >                                                pages + i);
> >                       break;
> >               case GUP_BASIC_TEST:
> > -                     nr = get_user_pages(addr, nr, gup->flags, pages + i,
> > +                     nr = get_user_pages(addr, nr, gup->gup_flags, pages + i,
> >                                           NULL);
> >                       break;
> >               case PIN_FAST_BENCHMARK:
> > -                     nr = pin_user_pages_fast(addr, nr, gup->flags,
> > +                     nr = pin_user_pages_fast(addr, nr, gup->gup_flags,
> >                                                pages + i);
> >                       break;
> >               case PIN_BASIC_TEST:
> > -                     nr = pin_user_pages(addr, nr, gup->flags, pages + i,
> > +                     nr = pin_user_pages(addr, nr, gup->gup_flags, pages + i,
> >                                           NULL);
> >                       break;
> >               case PIN_LONGTERM_BENCHMARK:
> >                       nr = pin_user_pages(addr, nr,
> > -                                         gup->flags | FOLL_LONGTERM,
> > +                                         gup->gup_flags | FOLL_LONGTERM,
> >                                           pages + i, NULL);
> >                       break;
> >               case DUMP_USER_PAGES_TEST:
> > -                     if (gup->flags & GUP_TEST_FLAG_DUMP_PAGES_USE_PIN)
> > -                             nr = pin_user_pages(addr, nr, gup->flags,
> > +                     if (gup->test_flags & GUP_TEST_FLAG_DUMP_PAGES_USE_PIN)
> > +                             nr = pin_user_pages(addr, nr, gup->gup_flags,
> >                                                   pages + i, NULL);
> >                       else
> > -                             nr = get_user_pages(addr, nr, gup->flags,
> > +                             nr = get_user_pages(addr, nr, gup->gup_flags,
> >                                                   pages + i, NULL);
> >                       break;
> >               default:
> > @@ -187,7 +184,7 @@ static int __gup_test_ioctl(unsigned int cmd,
> >
> >       start_time = ktime_get();
> >
> > -     put_back_pages(cmd, pages, nr_pages, gup->flags);
> > +     put_back_pages(cmd, pages, nr_pages, gup->test_flags);
> >
> >       end_time = ktime_get();
> >       gup->put_delta_usec = ktime_us_delta(end_time, start_time);
> > diff --git a/mm/gup_test.h b/mm/gup_test.h
> > index 90a6713d50eb..887ac1d5f5bc 100644
> > --- a/mm/gup_test.h
> > +++ b/mm/gup_test.h
> > @@ -21,7 +21,8 @@ struct gup_test {
> >       __u64 addr;
> >       __u64 size;
> >       __u32 nr_pages_per_call;
> > -     __u32 flags;
> > +     __u32 gup_flags;
> > +     __u32 test_flags;
> >       /*
> >        * Each non-zero entry is the number of the page (1-based: first page is
> >        * page 1, so that zero entries mean "do nothing") from the .addr base.
> > diff --git a/tools/testing/selftests/vm/gup_test.c b/tools/testing/selftests/vm/gup_test.c
> > index 6c6336dd3b7f..943cc2608dc2 100644
> > --- a/tools/testing/selftests/vm/gup_test.c
> > +++ b/tools/testing/selftests/vm/gup_test.c
> > @@ -37,13 +37,13 @@ int main(int argc, char **argv)
> >   {
> >       struct gup_test gup = { 0 };
> >       unsigned long size = 128 * MB;
> > -     int i, fd, filed, opt, nr_pages = 1, thp = -1, repeats = 1, write = 0;
> > +     int i, fd, filed, opt, nr_pages = 1, thp = -1, repeats = 1, write = 1;
> >       unsigned long cmd = GUP_FAST_BENCHMARK;
> >       int flags = MAP_PRIVATE;
> >       char *file = "/dev/zero";
> >       char *p;
> >
> > -     while ((opt = getopt(argc, argv, "m:r:n:F:f:abctTLUuwSH")) != -1) {
> > +     while ((opt = getopt(argc, argv, "m:r:n:F:f:abctTLUuwWSHp")) != -1) {
> >               switch (opt) {
> >               case 'a':
> >                       cmd = PIN_FAST_BENCHMARK;
> > @@ -65,9 +65,13 @@ int main(int argc, char **argv)
> >                        */
> >                       gup.which_pages[0] = 1;
> >                       break;
> > +             case 'p':
> > +                     /* works only with DUMP_USER_PAGES_TEST */
> > +                     gup.test_flags |= GUP_TEST_FLAG_DUMP_PAGES_USE_PIN;
> > +                     break;
> >               case 'F':
> >                       /* strtol, so you can pass flags in hex form */
> > -                     gup.flags = strtol(optarg, 0, 0);
> > +                     gup.gup_flags = strtol(optarg, 0, 0);
> >                       break;
> >               case 'm':
> >                       size = atoi(optarg) * MB;
> > @@ -93,6 +97,9 @@ int main(int argc, char **argv)
> >               case 'w':
> >                       write = 1;
> >                       break;
> > +             case 'W':
> > +                     write = 0;
> > +                     break;
> >               case 'f':
> >                       file = optarg;
> >                       break;
> > @@ -140,7 +147,7 @@ int main(int argc, char **argv)
> >
> >       gup.nr_pages_per_call = nr_pages;
> >       if (write)
> > -             gup.flags |= FOLL_WRITE;
> > +             gup.gup_flags |= FOLL_WRITE;
> >
> >       fd = open("/sys/kernel/debug/gup_test", O_RDWR);
> >       if (fd == -1) {
> >
>