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, 10 Mar 2021 14:59:04 +0000
From:   Russell King - ARM Linux admin <linux@armlinux.org.uk>
To:     Jan Kardell <jan.kardell@telliq.com>
Cc:     Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org,
        Tony Lindgren <tony@atomide.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org
Subject: Re: arm: lockdep complaining about locks allocations in static memory
Message-ID: <20210310145904.GA1470@shell.armlinux.org.uk>
References: <6df24716-8b41-8e9a-f2f4-a0f5d49643bd@telliq.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <6df24716-8b41-8e9a-f2f4-a0f5d49643bd@telliq.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Precedence: bulk

On Wed, Mar 10, 2021 at 02:54:30PM +0100, Jan Kardell wrote:
> Hi,
> 
> During work lift the software and kernel versions on our custom TI am3352
> board I started to see lockdep warnings after enabling CONFIG_PREEMT.
> Lockdep seems to think the memory that previously was initmem is static
> memory. I'm using linux 5.4, as that is what is used in the next OpenWrt
> version.
> 
> [ 92.198989] WARNING: CPU: 0 PID: 2015 at kernel/locking/lockdep.c:1119
> alloc_netdev_mqs+0xb4/0x3b0
> 
> I guess CONFIG_PREEMT just changes the timing of allocations, and is
> otherwise irrelevant.
> 
> This was fixed for s390 in linux 5.2 commit
> 7a5da02de8d6eafba99556f8c98e5313edebb449 by adding the function
> arch_is_kernel_initmem_freed(). Later a very similar change was made for
> powerpc, and a different solution for x86. I now believe that is needed for
> arm as well. Though I don't know the inner workings of arm memory management
> so I don't know if an identical solution to s390 will do for arm, but my
> experiments suggests it works for am335x. The commit message for s390 says
> "virt == phys", but that seems not to be the case for my arm system.

I don't see any reason this couldn't be added to arm, but it needs
someone to create and test a patch - which implies that they need to
have a problem that needs to be solved. As you seem to be experiencing
the problem, it seems you are well suited to this. Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!