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From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     linux-mm@kvack.org
Cc:     Andrea Arcangeli <aarcange@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        John Hubbard <jhubbard@nvidia.com>,
        =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= <jglisse@redhat.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        "Kuehling, Felix" <Felix.Kuehling@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>,
        "David (ChunMing) Zhou" <David1.Zhou@amd.com>,
        Dimitri Sivanich <sivanich@sgi.com>,
        dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
        iommu@lists.linux-foundation.org, intel-gfx@lists.freedesktop.org,
        Gavin Shan <shangw@linux.vnet.ibm.com>,
        Andrea Righi <andrea@betterlinux.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Christoph Hellwig <hch@infradead.org>
Subject: [PATCH v3 hmm 01/11] mm/mmu_notifiers: hoist do_mmu_notifier_register down_write to the caller
Date:   Tue,  6 Aug 2019 20:15:38 -0300
Message-Id: <20190806231548.25242-2-jgg@ziepe.ca>
In-Reply-To: <20190806231548.25242-1-jgg@ziepe.ca>
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From: Jason Gunthorpe <jgg@mellanox.com>

This simplifies the code to not have so many one line functions and extra
logic. __mmu_notifier_register() simply becomes the entry point to
register the notifier, and the other one calls it under lock.

Also add a lockdep_assert to check that the callers are holding the lock
as expected.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
 mm/mmu_notifier.c | 35 ++++++++++++++---------------------
 1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index b5670620aea0fc..218a6f108bc2d0 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -236,22 +236,22 @@ void __mmu_notifier_invalidate_range(struct mm_struct *mm,
 }
 EXPORT_SYMBOL_GPL(__mmu_notifier_invalidate_range);
 
-static int do_mmu_notifier_register(struct mmu_notifier *mn,
-				    struct mm_struct *mm,
-				    int take_mmap_sem)
+/*
+ * Same as mmu_notifier_register but here the caller must hold the
+ * mmap_sem in write mode.
+ */
+int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 {
 	struct mmu_notifier_mm *mmu_notifier_mm;
 	int ret;
 
+	lockdep_assert_held_write(&mm->mmap_sem);
 	BUG_ON(atomic_read(&mm->mm_users) <= 0);
 
-	ret = -ENOMEM;
 	mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
 	if (unlikely(!mmu_notifier_mm))
-		goto out;
+		return -ENOMEM;
 
-	if (take_mmap_sem)
-		down_write(&mm->mmap_sem);
 	ret = mm_take_all_locks(mm);
 	if (unlikely(ret))
 		goto out_clean;
@@ -279,13 +279,11 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
 
 	mm_drop_all_locks(mm);
 out_clean:
-	if (take_mmap_sem)
-		up_write(&mm->mmap_sem);
 	kfree(mmu_notifier_mm);
-out:
 	BUG_ON(atomic_read(&mm->mm_users) <= 0);
 	return ret;
 }
+EXPORT_SYMBOL_GPL(__mmu_notifier_register);
 
 /*
  * Must not hold mmap_sem nor any other VM related lock when calling
@@ -302,19 +300,14 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
  */
 int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 {
-	return do_mmu_notifier_register(mn, mm, 1);
-}
-EXPORT_SYMBOL_GPL(mmu_notifier_register);
+	int ret;
 
-/*
- * Same as mmu_notifier_register but here the caller must hold the
- * mmap_sem in write mode.
- */
-int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
-{
-	return do_mmu_notifier_register(mn, mm, 0);
+	down_write(&mm->mmap_sem);
+	ret = __mmu_notifier_register(mn, mm);
+	up_write(&mm->mmap_sem);
+	return ret;
 }
-EXPORT_SYMBOL_GPL(__mmu_notifier_register);
+EXPORT_SYMBOL_GPL(mmu_notifier_register);
 
 /* this is called after the last mmu_notifier_unregister() returned */
 void __mmu_notifier_mm_destroy(struct mm_struct *mm)
-- 
2.22.0