linux-kernel - [PATCH] mm: document mmu_notifier_invalidate_range_start

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Date:   Mon, 18 Sep 2023 22:18:32 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alistair Popple <apopple@...dia.com>,
        Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH] mm: document mmu_notifier_invalidate_range_start_nonblock()

Document what mmu_notifier_invalidate_range_start_nonblock() is for.
Also add a __must_check annotation to signal that callers must bail out if
a notifier vetoes the operation.

Signed-off-by: Jann Horn <jannh@...gle.com>
---
 include/linux/mmu_notifier.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 6e3c857606f1..f349e08a9dfe 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -459,7 +459,14 @@ mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
 	lock_map_release(&__mmu_notifier_invalidate_range_start_map);
 }
 
-static inline int
+/*
+ * This version of mmu_notifier_invalidate_range_start() avoids blocking, but it
+ * can return an error if a notifier can't proceed without blocking, in which
+ * case you're not allowed to modify PTEs in the specified range.
+ *
+ * This is mainly intended for OOM handling.
+ */
+static inline int __must_check
 mmu_notifier_invalidate_range_start_nonblock(struct mmu_notifier_range *range)
 {
 	int ret = 0;

base-commit: 6704c78e2963a5682b4ac3c0e609d36f2405cf17
-- 
2.42.0.459.ge4e396fd5e-goog