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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id z126sm884276qkb.7.2019.06.13.17.44.54 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 13 Jun 2019 17:44:54 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hbaKr-0005K2-Rs; Thu, 13 Jun 2019 21:44:53 -0300 From: Jason Gunthorpe To: Jerome Glisse , Ralph Campbell , John Hubbard , Felix.Kuehling@amd.com Cc: linux-rdma@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, Ben Skeggs , Jason Gunthorpe , Philip Yang Subject: [PATCH v3 hmm 06/12] mm/hmm: Hold on to the mmget for the lifetime of the range Date: Thu, 13 Jun 2019 21:44:44 -0300 Message-Id: <20190614004450.20252-7-jgg@ziepe.ca> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190614004450.20252-1-jgg@ziepe.ca> References: <20190614004450.20252-1-jgg@ziepe.ca> MIME-Version: 1.0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP From: Jason Gunthorpe Range functions like hmm_range_snapshot() and hmm_range_fault() call find_vma, which requires hodling the mmget() and the mmap_sem for the mm. Make this simpler for the callers by holding the mmget() inside the range for the lifetime of the range. Other functions that accept a range should only be called if the range is registered. This has the side effect of directly preventing hmm_release() from happening while a range is registered. That means range->dead cannot be false during the lifetime of the range, so remove dead and hmm_mirror_mm_is_alive() entirely. Signed-off-by: Jason Gunthorpe Reviewed-by: John Hubbard Reviewed-by: Ralph Campbell Tested-by: Philip Yang Reviewed-by: Christoph Hellwig --- v2: - Use Jerome's idea of just holding the mmget() for the range lifetime, rework the patch to use that as as simplification to remove dead in one step --- include/linux/hmm.h | 26 -------------------------- mm/hmm.c | 28 ++++++++++------------------ 2 files changed, 10 insertions(+), 44 deletions(-) diff --git a/include/linux/hmm.h b/include/linux/hmm.h index 26e7c477490c4e..bf013e96525771 100644 --- a/include/linux/hmm.h +++ b/include/linux/hmm.h @@ -82,7 +82,6 @@ * @mirrors_sem: read/write semaphore protecting the mirrors list * @wq: wait queue for user waiting on a range invalidation * @notifiers: count of active mmu notifiers - * @dead: is the mm dead ? */ struct hmm { struct mm_struct *mm; @@ -95,7 +94,6 @@ struct hmm { wait_queue_head_t wq; struct rcu_head rcu; long notifiers; - bool dead; }; /* @@ -459,30 +457,6 @@ 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 - * Return: false if the mm is dead, true otherwise - * - * This is an optimization, it will not always accurately return false if the - * mm is dead; i.e., there can be false negatives (process is being killed but - * HMM is not yet informed of that). It is only intended to be used to optimize - * out cases where the 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. */ diff --git a/mm/hmm.c b/mm/hmm.c index 4c64d4c32f4825..58712d74edd585 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -70,7 +70,6 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm) mutex_init(&hmm->lock); kref_init(&hmm->kref); hmm->notifiers = 0; - hmm->dead = false; hmm->mm = mm; hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops; @@ -125,20 +124,17 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) { struct hmm *hmm = container_of(mn, struct hmm, mmu_notifier); struct hmm_mirror *mirror; - struct hmm_range *range; /* Bail out if hmm is in the process of being freed */ if (!kref_get_unless_zero(&hmm->kref)) return; - /* Report this HMM as dying. */ - hmm->dead = true; - - /* Wake-up everyone waiting on any range. */ mutex_lock(&hmm->lock); - list_for_each_entry(range, &hmm->ranges, list) - range->valid = false; - wake_up_all(&hmm->wq); + /* + * Since hmm_range_register() holds the mmget() lock hmm_release() is + * prevented as long as a range exists. + */ + WARN_ON(!list_empty(&hmm->ranges)); mutex_unlock(&hmm->lock); down_write(&hmm->mirrors_sem); @@ -908,8 +904,8 @@ int hmm_range_register(struct hmm_range *range, range->start = start; range->end = end; - /* Check if hmm_mm_destroy() was call. */ - if (hmm->mm == NULL || hmm->dead) + /* Prevent hmm_release() from running while the range is valid */ + if (!mmget_not_zero(hmm->mm)) return -EFAULT; /* Initialize range to track CPU page table updates. */ @@ -952,6 +948,7 @@ void hmm_range_unregister(struct hmm_range *range) /* Drop reference taken by hmm_range_register() */ range->valid = false; + mmput(hmm->mm); hmm_put(hmm); range->hmm = NULL; } @@ -979,10 +976,7 @@ long hmm_range_snapshot(struct hmm_range *range) struct vm_area_struct *vma; struct mm_walk mm_walk; - /* Check if hmm_mm_destroy() was call. */ - if (hmm->mm == NULL || hmm->dead) - return -EFAULT; - + lockdep_assert_held(&hmm->mm->mmap_sem); do { /* If range is no longer valid force retry. */ if (!range->valid) @@ -1077,9 +1071,7 @@ long hmm_range_fault(struct hmm_range *range, bool block) struct mm_walk mm_walk; int ret; - /* Check if hmm_mm_destroy() was call. */ - if (hmm->mm == NULL || hmm->dead) - return -EFAULT; + lockdep_assert_held(&hmm->mm->mmap_sem); do { /* If range is no longer valid force retry. */