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Date:   Thu, 17 Aug 2023 12:41:32 +0200
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To:     Linux Media Mailing List <linux-media@vger.kernel.org>
Cc:     Marek Szyprowski <m.szyprowski@samsung.com>,
        Tomasz Figa <tfiga@chromium.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Jan Kara <jack@suse.cz>, David Hildenbrand <david@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
From:   Hans Verkuil <hverkuil-cisco@xs4all.nl>
Subject: [PATCH] media: vb2: frame_vector.c: replace WARN_ONCE with a comment
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The WARN_ONCE was issued also in cases that had nothing to do with VM_IO
(e.g. if the start address was just a random value and uaccess fails with
-EFAULT).

There are no reports of WARN_ONCE being issued for actual VM_IO cases, so
just drop it and instead add a note to the comment before the function.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
---
diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c
index 0f430ddc1f67..fd87747be9b1 100644
--- a/drivers/media/common/videobuf2/frame_vector.c
+++ b/drivers/media/common/videobuf2/frame_vector.c
@@ -31,6 +31,10 @@
  * different type underlying the specified range of virtual addresses.
  * When the function isn't able to map a single page, it returns error.
  *
+ * Note that get_vaddr_frames() cannot follow VM_IO mappings. It used
+ * to be able to do that, but that could (racily) return non-refcounted
+ * pfns.
+ *
  * This function takes care of grabbing mmap_lock as necessary.
  */
 int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
@@ -59,8 +63,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
 	if (likely(ret > 0))
 		return ret;

-	/* This used to (racily) return non-refcounted pfns. Let people know */
-	WARN_ONCE(1, "get_vaddr_frames() cannot follow VM_IO mapping");
 	vec->nr_frames = 0;
 	return ret ? ret : -EFAULT;
 }