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From: Christoph Hellwig <hch@lst.de>
To: "Dan Williams" <dan.j.williams@intel.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Jason Gunthorpe" <jgg@mellanox.com>,
	"Ben Skeggs" <bskeggs@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>,
	linux-mm@kvack.org, nouveau@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org, linux-nvdimm@lists.01.org,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	Philip Yang <Philip.Yang@amd.com>
Subject: [PATCH 16/22] mm/hmm: Remove confusing comment and logic from hmm_release
Date: Mon,  1 Jul 2019 08:20:14 +0200	[thread overview]
Message-ID: <20190701062020.19239-17-hch@lst.de> (raw)
In-Reply-To: <20190701062020.19239-1-hch@lst.de>

From: Jason Gunthorpe <jgg@mellanox.com>

hmm_release() is called exactly once per hmm. ops->release() cannot
accidentally trigger any action that would recurse back onto
hmm->mirrors_sem.

This fixes a use after-free race of the form:

       CPU0                                   CPU1
                                           hmm_release()
                                             up_write(&hmm->mirrors_sem);
 hmm_mirror_unregister(mirror)
  down_write(&hmm->mirrors_sem);
  up_write(&hmm->mirrors_sem);
  kfree(mirror)
                                             mirror->ops->release(mirror)

The only user we have today for ops->release is an empty function, so this
is unambiguously safe.

As a consequence of plugging this race drivers are not allowed to
register/unregister mirrors from within a release op.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Philip Yang <Philip.Yang@amd.com>
---
 mm/hmm.c | 28 +++++++++-------------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index c30aa9403dbe..b224ea635a77 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -130,26 +130,16 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
 	 */
 	WARN_ON(!list_empty_careful(&hmm->ranges));
 
-	down_write(&hmm->mirrors_sem);
-	mirror = list_first_entry_or_null(&hmm->mirrors, struct hmm_mirror,
-					  list);
-	while (mirror) {
-		list_del_init(&mirror->list);
-		if (mirror->ops->release) {
-			/*
-			 * Drop mirrors_sem so the release callback can wait
-			 * on any pending work that might itself trigger a
-			 * mmu_notifier callback and thus would deadlock with
-			 * us.
-			 */
-			up_write(&hmm->mirrors_sem);
+	down_read(&hmm->mirrors_sem);
+	list_for_each_entry(mirror, &hmm->mirrors, list) {
+		/*
+		 * Note: The driver is not allowed to trigger
+		 * hmm_mirror_unregister() from this thread.
+		 */
+		if (mirror->ops->release)
 			mirror->ops->release(mirror);
-			down_write(&hmm->mirrors_sem);
-		}
-		mirror = list_first_entry_or_null(&hmm->mirrors,
-						  struct hmm_mirror, list);
 	}
-	up_write(&hmm->mirrors_sem);
+	up_read(&hmm->mirrors_sem);
 
 	hmm_put(hmm);
 }
@@ -279,7 +269,7 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror)
 	struct hmm *hmm = mirror->hmm;
 
 	down_write(&hmm->mirrors_sem);
-	list_del_init(&mirror->list);
+	list_del(&mirror->list);
 	up_write(&hmm->mirrors_sem);
 	hmm_put(hmm);
 }
-- 
2.20.1


  parent reply	other threads:[~2019-07-01  6:21 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-01  6:19 dev_pagemap related cleanups v4 Christoph Hellwig
2019-07-01  6:19 ` [PATCH 01/22] mm/hmm.c: suppress compilation warnings when CONFIG_HUGETLB_PAGE is not set Christoph Hellwig
2019-07-01  6:20 ` [PATCH 02/22] mm/hmm: update HMM documentation Christoph Hellwig
2019-07-01  6:20 ` [PATCH 03/22] mm/hmm: clean up some coding style and comments Christoph Hellwig
2019-07-01  6:20 ` [PATCH 04/22] mm/hmm: support automatic NUMA balancing Christoph Hellwig
2019-07-01  6:20 ` [PATCH 05/22] mm/hmm: Only set FAULT_FLAG_ALLOW_RETRY for non-blocking Christoph Hellwig
2019-07-01  6:20 ` [PATCH 06/22] mm/hmm: fix use after free with struct hmm in the mmu notifiers Christoph Hellwig
2019-07-01  6:20 ` [PATCH 07/22] mm/hmm: Use hmm_mirror not mm as an argument for hmm_range_register Christoph Hellwig
2019-07-01  6:20 ` [PATCH 08/22] mm/hmm: Hold a mmgrab from hmm to mm Christoph Hellwig
2019-07-01  6:20 ` [PATCH 09/22] mm/hmm: Simplify hmm_get_or_create and make it reliable Christoph Hellwig
2019-07-01  6:20 ` [PATCH 10/22] mm/hmm: Remove duplicate condition test before wait_event_timeout Christoph Hellwig
2019-07-01  6:20 ` [PATCH 11/22] mm/hmm: Do not use list*_rcu() for hmm->ranges Christoph Hellwig
2019-07-01  6:20 ` [PATCH 12/22] mm/hmm: Hold on to the mmget for the lifetime of the range Christoph Hellwig
2019-07-01  6:20 ` [PATCH 13/22] mm/hmm: Use lockdep instead of comments Christoph Hellwig
2019-07-01  6:20 ` [PATCH 14/22] mm/hmm: Remove racy protection against double-unregistration Christoph Hellwig
2019-07-01  6:20 ` [PATCH 15/22] mm/hmm: Poison hmm_range during unregister Christoph Hellwig
2019-07-01  6:20 ` Christoph Hellwig [this message]
2019-07-01  6:20 ` [PATCH 17/22] mm/hmm: Fix error flows in hmm_invalidate_range_start Christoph Hellwig
2019-07-01  6:20 ` [PATCH 18/22] mm: return valid info from hmm_range_unregister Christoph Hellwig
2019-07-03 17:22   ` Ralph Campbell
2019-07-01  6:20 ` [PATCH 19/22] mm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot} Christoph Hellwig
2019-07-02 21:43   ` Kuehling, Felix
2019-07-03 17:32   ` Ralph Campbell
2019-07-01  6:20 ` [PATCH 20/22] mm: move hmm_vma_fault to nouveau Christoph Hellwig
2019-07-03 17:48   ` Ralph Campbell
2019-07-03 17:50     ` [Nouveau] " Ilia Mirkin
2019-07-03 18:03   ` Jason Gunthorpe
2019-07-03 18:05     ` Christoph Hellwig
2019-07-03 18:13       ` Jason Gunthorpe
2019-07-01  6:20 ` [PATCH 21/22] nouveau: unlock mmap_sem on all errors from nouveau_range_fault Christoph Hellwig
2019-07-01  6:20 ` [PATCH 22/22] mm: remove the legacy hmm_pfn_* APIs Christoph Hellwig
2019-07-03 18:01   ` Jason Gunthorpe
2019-07-03 18:03     ` Christoph Hellwig
2019-07-03 18:15       ` Jason Gunthorpe
2019-07-01  8:25 ` dev_pagemap related cleanups v4 Christoph Hellwig
2019-07-02 18:42   ` Jason Gunthorpe
2019-07-02 22:45     ` Weiny, Ira
2019-07-02 22:47       ` Christoph Hellwig
2019-07-02 23:17     ` Dan Williams
2019-07-03  1:08       ` Jason Gunthorpe

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