linux-kernel - [PATCH] userfaultfd: wake on unregister for minor faults as well as missing

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Date:   Tue, 25 Oct 2022 11:21:49 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Axel Rasmussen <axelrasmussen@...gle.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH] userfaultfd: wake on unregister for minor faults as well as missing

This was an overlooked edge case when minor faults were added. In
general, minor faults have the same rough edge here as missing faults:
if we unregister while there are waiting threads, they will just remain
waiting forever, as there is no way for userspace to wake them after
unregistration. To work around this, userspace needs to carefully wake
everything before unregistering.

So, wake for minor faults just like we already do for missing faults as
part of the unregistration process.

Cc: stable@...r.kernel.org
Fixes: 7677f7fd8be7 ("userfaultfd: add minor fault registration mode")
Reported-by: Lokesh Gidra <lokeshgidra@...gle.com>
Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
---
 fs/userfaultfd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 07c81ab3fd4d..7daee4b9481c 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1606,7 +1606,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 			start = vma->vm_start;
 		vma_end = min(end, vma->vm_end);
 
-		if (userfaultfd_missing(vma)) {
+		if (userfaultfd_missing(vma) || userfaultfd_minor(vma)) {
 			/*
 			 * Wake any concurrent pending userfault while
 			 * we unregister, so they will not hang
-- 
2.38.0.135.g90850a2211-goog