Add tests to assert that PIDFD_SELF* correctly refers to the current thread and process. We explicitly test pidfd_send_signal(), however We defer testing of mm-specific functionality which uses pidfd, namely process_madvise() and process_mrelease() to mm testing (though note the latter can not be sensibly tested as it would require the testing process to be dying). We also correct the pidfd_open_test.c fields which refer to .request_mask whereas the UAPI header refers to .mask, which otherwise break the import of the UAPI header. Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Link: https://lore.kernel.org/r/7ab0e48b26ba53abf7b703df2dd11a2e99b8efb2.1738268370.git.lorenzo.stoakes@oracle.com Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev> Signed-off-by: Christian Brauner <brauner@kernel.org> (cherry picked from commit 2bbf47f2d396ee32068042a99ecf4da955ce88ec) [surenb: skipped changes in pidfd_open_test.c since the checks that were changed do not exist in 6.12] Bug: 402449065 Change-Id: I8fa8848e7028363ea09d7cf4aca5611bb7fdd95c Signed-off-by: Suren Baghdasaryan <surenb@google.com>