linux-kernel - [PATCH 1/2] mm: replace BUG_ON in vm_insert

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Message-Id: <20210203003134.2422308-1-surenb@google.com>
Date:   Tue,  2 Feb 2021 16:31:33 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     sumit.semwal@...aro.org
Cc:     akpm@...ux-foundation.org, hch@...radead.org, lmark@...eaurora.org,
        labbott@...hat.com, Brian.Starkey@....com, john.stultz@...aro.org,
        christian.koenig@....com, cgoldswo@...eaurora.org,
        orjan.eide@....com, robin.murphy@....com, jajones@...dia.com,
        minchan@...nel.org, hridya@...gle.com, sspatil@...gle.com,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        surenb@...gle.com
Subject: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return of an error

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@...radead.org>
Signed-off-by: Suren Baghdasaryan <surenb@...gle.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