[LTP] [PATCH 3/3] fanotify24: add mmap() and user page fault to test

[Amir Goldstein]

On Thu, Mar 20, 2025 at 6:00 PM Petr Vorel <pvorel@suse.cz> wrote:
>
> Hi Amir,
>
> > Commit 066e053fe208a ("fsnotify: add pre-content hooks on mmap()")
> > in 6.14-rc7 added a pre-content hooh in mmap() before the final release
> > of the fsnotify pre-content event feature.
>
> > To test pre-content hook on mmap(), increase the size of the test file
> > to 101 pages use mmap() to setup a buffer from the end of the test file.
>
> > Change some of the test cases to allow the write() and use this buffer
> > as the input buffer to write(), which tests deadlock avoidance by
> > suppresing pre-content hook on user page faults.
>
> > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > ---
> >  .../kernel/syscalls/fanotify/fanotify24.c     | 41 ++++++++++++++++---
> >  1 file changed, 35 insertions(+), 6 deletions(-)
>
> > diff --git a/testcases/kernel/syscalls/fanotify/fanotify24.c b/testcases/kernel/syscalls/fanotify/fanotify24.c
> > index 2d2479b39..3a76f2c1b 100644
> > --- a/testcases/kernel/syscalls/fanotify/fanotify24.c
> > +++ b/testcases/kernel/syscalls/fanotify/fanotify24.c
> > @@ -46,6 +46,7 @@
> >  static char fname[BUF_SIZE];
> >  static char buf[BUF_SIZE];
> >  static volatile int fd_notify;
> > +static size_t page_sz;
>
> >  static pid_t child_pid;
>
> > @@ -68,7 +69,8 @@ static struct tcase {
> >               FAN_OPEN_PERM | FAN_PRE_ACCESS,
> >               {
> >                       {FAN_OPEN_PERM, FAN_ALLOW},
> > -                     {FAN_PRE_ACCESS, FAN_DENY},
> > +                     {FAN_PRE_ACCESS, FAN_ALLOW},
> > +                     {FAN_PRE_ACCESS, FAN_ALLOW},
>
> If I understand correctly, these doubled FAN_PRE_ACCESS, FAN_ALLOW are for
> reusing the write buffer, right? Obviously it's needed but on the first look it
> looks like error.

Sorry, this wasn't properly explained.

This change adds a test for pre-mmap events.

First of all, we added an mmap() call before the write(),
so we need to add another expected FAN_PRE_ACCESS
for the mmap() and we allow the mmap for all test cases.

Secondly, we Change some of the test cases to allow the write()
and use the mmaped buffer as the input buffer.

The reason that we allow the write() is to verify that we do not
get another FAN_PRE_ACCESS event from reading from the
mmaped input buffer.

Thanks,
Amir.