From c01cbba2aa8b4d05607d373b02fe9e4eda5c0591 Mon Sep 17 00:00:00 2001 From: =?utf8?q?J=C3=A9r=C3=B4me=20Glisse?= Date: Tue, 10 Apr 2018 16:28:23 -0700 Subject: [PATCH] mm/hmm: unregister mmu_notifier when last HMM client quit MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This code was lost in translation at one point. This properly call mmu_notifier_unregister_no_release() once last user is gone. This fix the zombie mm_struct as without this patch we do not drop the refcount we have on it. Link: http://lkml.kernel.org/r/20180323005527.758-5-jglisse@redhat.com Signed-off-by: Jérôme Glisse Cc: Evgeny Baskakov Cc: Ralph Campbell Cc: Mark Hairgrove Cc: John Hubbard Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hmm.c | 38 +++++++++++++++++++++++++++++++++++--- 1 file changed, 35 insertions(+), 3 deletions(-) diff --git a/mm/hmm.c b/mm/hmm.c index 8116727766f7..2d00769e8985 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -233,13 +233,24 @@ int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm) if (!mm || !mirror || !mirror->ops) return -EINVAL; +again: mirror->hmm = hmm_register(mm); if (!mirror->hmm) return -ENOMEM; down_write(&mirror->hmm->mirrors_sem); - list_add(&mirror->list, &mirror->hmm->mirrors); - up_write(&mirror->hmm->mirrors_sem); + if (mirror->hmm->mm == NULL) { + /* + * A racing hmm_mirror_unregister() is about to destroy the hmm + * struct. Try again to allocate a new one. + */ + up_write(&mirror->hmm->mirrors_sem); + mirror->hmm = NULL; + goto again; + } else { + list_add(&mirror->list, &mirror->hmm->mirrors); + up_write(&mirror->hmm->mirrors_sem); + } return 0; } @@ -254,11 +265,32 @@ EXPORT_SYMBOL(hmm_mirror_register); */ void hmm_mirror_unregister(struct hmm_mirror *mirror) { - struct hmm *hmm = mirror->hmm; + bool should_unregister = false; + struct mm_struct *mm; + struct hmm *hmm; + + if (mirror->hmm == NULL) + return; + hmm = mirror->hmm; down_write(&hmm->mirrors_sem); list_del_init(&mirror->list); + should_unregister = list_empty(&hmm->mirrors); + mirror->hmm = NULL; + mm = hmm->mm; + hmm->mm = NULL; up_write(&hmm->mirrors_sem); + + if (!should_unregister || mm == NULL) + return; + + spin_lock(&mm->page_table_lock); + if (mm->hmm == hmm) + mm->hmm = NULL; + spin_unlock(&mm->page_table_lock); + + mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm); + kfree(hmm); } EXPORT_SYMBOL(hmm_mirror_unregister); -- 2.30.2