From 202394178d027f8a1530df65d4a25229138fab62 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= Date: Mon, 13 May 2019 17:20:24 -0700 Subject: [PATCH] mm/hmm: add helpers to test if mm is still alive or not MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The device driver can have kernel thread or worker doing work against a process mm and it is useful for those to test wether the mm is dead or alive to avoid doing useless work. Add an helper to test that so that driver can bail out early if a process is dying. Note that the helper does not perform any lock synchronization and thus is just a hint ie a process might be dying but the helper might still return the process as alive. All HMM functions are safe to use in that case as HMM internal properly protect itself with lock. If driver use this helper with non HMM functions it should ascertain that it is safe to do so. Link: http://lkml.kernel.org/r/20190403193318.16478-11-jglisse@redhat.com Signed-off-by: Jérôme Glisse Cc: Ralph Campbell Cc: John Hubbard Cc: Dan Williams Cc: Ira Weiny Cc: Arnd Bergmann Cc: Balbir Singh Cc: Dan Carpenter Cc: Matthew Wilcox Cc: Souptick Joarder Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/hmm.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/include/linux/hmm.h b/include/linux/hmm.h index e5834082de60..a79fcc6681f5 100644 --- a/include/linux/hmm.h +++ b/include/linux/hmm.h @@ -438,6 +438,30 @@ struct hmm_mirror { int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm); void hmm_mirror_unregister(struct hmm_mirror *mirror); +/* + * hmm_mirror_mm_is_alive() - test if mm is still alive + * @mirror: the HMM mm mirror for which we want to lock the mmap_sem + * Returns: false if the mm is dead, true otherwise + * + * This is an optimization it will not accurately always return -EINVAL if the + * mm is dead ie there can be false negative (process is being kill but HMM is + * not yet inform of that). It is only intented to be use to optimize out case + * where driver is about to do something time consuming and it would be better + * to skip it if the mm is dead. + */ +static inline bool hmm_mirror_mm_is_alive(struct hmm_mirror *mirror) +{ + struct mm_struct *mm; + + if (!mirror || !mirror->hmm) + return false; + mm = READ_ONCE(mirror->hmm->mm); + if (mirror->hmm->dead || !mm) + return false; + + return true; +} + /* * Please see Documentation/vm/hmm.rst for how to use the range API. -- GitLab