From: Suren Baghdasaryan <surenb@google.com>
Date: Wed, 19 Oct 2022 20:12:19 +0000 (+0000)
Subject: mm: perform VMA walk in find_mergeable_anon_vma under RCU read lock
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=d3f6a897b96314e6e3b63f254bcbf5963dbbbb0c;p=users%2Fjedix%2Flinux-maple.git

mm: perform VMA walk in find_mergeable_anon_vma under RCU read lock

find_mergeable_anon_vma walks VMA tree unders assumption that the caller
holds mmap_lock for write. Perform this walk under RCU protection to make
it safe without holding this lock.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---

diff --git a/mm/mmap.c b/mm/mmap.c
index 5e2193f59a8d..ee8dc559a66c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1169,12 +1169,20 @@ struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
 	struct anon_vma *anon_vma = NULL;
 	struct vm_area_struct *prev, *next;
 
+	/*
+	 * This search can be done with per-vma lock and without mmap_lock,
+	 * therefore acquire RCU read lock to prevent the tree from changing.
+	 */
+	rcu_read_lock();
+
 	/* Try next first. */
 	next = mas_walk(&mas);
 	if (next) {
 		anon_vma = reusable_anon_vma(next, vma, next);
-		if (anon_vma)
+		if (anon_vma) {
+			rcu_read_unlock();
 			return anon_vma;
+		}
 	}
 
 	prev = mas_prev(&mas, 0);
@@ -1184,6 +1192,7 @@ struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
 	if (prev)
 		anon_vma = reusable_anon_vma(prev, prev, vma);
 
+	rcu_read_unlock();
 	/*
 	 * We might reach here with anon_vma == NULL if we can't find
 	 * any reusable anon_vma.