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Date:   Tue,  2 Feb 2021 16:31:33 -0800
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Subject: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return of an error
From:   Suren Baghdasaryan <surenb@google.com>
To:     sumit.semwal@linaro.org
Cc:     akpm@linux-foundation.org, hch@infradead.org, lmark@codeaurora.org,
        labbott@redhat.com, Brian.Starkey@arm.com, john.stultz@linaro.org,
        christian.koenig@amd.com, cgoldswo@codeaurora.org,
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        minchan@kernel.org, hridya@google.com, sspatil@google.com,
        linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com,
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Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
WARN_ON_ONCE and returning an error. This is to ensure users of the
vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
and get an indication of an error without panicing the kernel.
This will help identifying drivers that need to clear VM_PFNMAP before
using dmabuf system heap which is moving to use vm_insert_page.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/memory.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index feff48e1465a..e503c9801cd9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1827,7 +1827,8 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
 		return -EINVAL;
 	if (!(vma->vm_flags & VM_MIXEDMAP)) {
 		BUG_ON(mmap_read_trylock(vma->vm_mm));
-		BUG_ON(vma->vm_flags & VM_PFNMAP);
+		if (WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP))
+			return -EINVAL;
 		vma->vm_flags |= VM_MIXEDMAP;
 	}
 	return insert_page(vma, addr, page, vma->vm_page_prot);
-- 
2.30.0.365.g02bc693789-goog