Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 3 Feb 2021 01:55:53 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     sumit.semwal@linaro.org, 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
Subject: Re: [PATCH 1/2] mm: replace BUG_ON in vm_insert_page with a return
 of an error
Message-ID: <20210203015553.GX308988@casper.infradead.org>
References: <20210203003134.2422308-1-surenb@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210203003134.2422308-1-surenb@google.com>
Precedence: bulk

On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
> 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.

NACK.

The system may not _panic_, but it is clearly now _broken_.  The device
doesn't work, and so the system is useless.  You haven't really improved
anything here.  Just bloated the kernel with yet another _ONCE variable
that in a normal system will never ever ever be triggered.