linux-kernel - [PATCH 2/5] mm, notifier: Prime lockdep

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Message-Id: <20190826201425.17547-3-daniel.vetter@ffwll.ch>
Date:   Mon, 26 Aug 2019 22:14:22 +0200
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Linux MM <linux-mm@...ck.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Christian König <christian.koenig@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: [PATCH 2/5] mm, notifier: Prime lockdep

We want to teach lockdep that mmu notifiers can be called from direct
reclaim paths, since on many CI systems load might never reach that
level (e.g. when just running fuzzer or small functional tests).

Motivated by a discussion with Jason.

I've put the annotation into mmu_notifier_register since only when we
have mmu notifiers registered is there any point in teaching lockdep
about them. Also, we already have a kmalloc(, GFP_KERNEL), so this is
safe.

Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Rientjes <rientjes@...gle.com>
Cc: "Jérôme Glisse" <jglisse@...hat.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: "Christian König" <christian.koenig@....com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>
Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc: linux-mm@...ck.org
Reviewed-by: Jason Gunthorpe <jgg@...lanox.com>
Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
---
 mm/mmu_notifier.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index d48d3b2abd68..0523555933c9 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -259,6 +259,13 @@ int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
 	lockdep_assert_held_write(&mm->mmap_sem);
 	BUG_ON(atomic_read(&mm->mm_users) <= 0);
 
+	if (IS_ENABLED(CONFIG_LOCKDEP)) {
+		fs_reclaim_acquire(GFP_KERNEL);
+		lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
+		lock_map_release(&__mmu_notifier_invalidate_range_start_map);
+		fs_reclaim_release(GFP_KERNEL);
+	}
+
 	mn->mm = mm;
 	mn->users = 1;
 
-- 
2.23.0