From: Suren Baghdasaryan <surenb@google.com>
Date: Sun, 30 Oct 2022 17:34:25 +0000 (+0000)
Subject: mm: prevent userfaults to be handled under per-vma lock
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=b2633cdddc62f05f62363ae03a1b6ee3925d88c0;p=users%2Fjedix%2Flinux-maple.git

mm: prevent userfaults to be handled under per-vma lock

Due to the possibility of handle_userfault dropping mmap_lock, avoid fault
handling under VMA lock and retry holding mmap_lock. This can be handled
more gracefully in the future.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Suggested-by: Peter Xu <peterx@redhat.com>
---

diff --git a/mm/memory.c b/mm/memory.c
index f528d0ea3671..e618481d6b52 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5267,6 +5267,13 @@ retry:
 	if (!vma_is_anonymous(vma))
 		goto inval;
 
+	/*
+	* Due to the possibility of userfault handler dropping mmap_lock, avoid
+	* it for now and fall back to page fault handling under mmap_lock.
+	*/
+	if (userfaultfd_armed(vma))
+		goto inval;
+
 	if (!vma_read_trylock(vma)) {
 		count_vm_vma_lock_event(VMA_LOCK_ABORT);
 		goto inval;