[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, orjan.eide@arm.com,
	robin.murphy@arm.com, jajones@nvidia.com, 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,
	surenb@google.com
Subject: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return of an error
Date: Tue,  2 Feb 2021 16:31:33 -0800	[thread overview]
Message-ID: <20210203003134.2422308-1-surenb@google.com> (raw)

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

