From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Wed, 1 Jul 2015 19:57:22 +0100 Subject: Oops at boot after commit 965278dcb8ab... when using split memory region In-Reply-To: <20150701180618.GI2310@leverpostej> References: <20150701144612.GG2310@leverpostej> <20150701145354.GL7557@n2100.arm.linux.org.uk> <20150701154007.GH2310@leverpostej> <20150701180618.GI2310@leverpostej> Message-ID: <20150701185722.GN7557@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Jul 01, 2015 at 07:06:19PM +0100, Mark Rutland wrote: > On Wed, Jul 01, 2015 at 04:40:07PM +0100, Mark Rutland wrote: > > Certainly. I did not mean to imply otherwise. > > > > Using a similar command line I can reproduce the issue on TC2, getting a > > hang when freeing unused kernel memory. I'm digging into that now. > > If I pass mem=56316K at 0${MY_MEM_BASE} (i.e. 55M - 4K), I get hangs with > and without commit 965278dcb8ab. It looks like we have a latent bug when > a bank is insufficiently aligned, and my patch increased that necessary > alignment from 1M to 2M. It's not a latent bug. I've _always_ said that memory banks _must_ be aligned to a section boundary, because that's what the ARM MM layer has been coded for. Yes, we've recently been _trying_ to relax that restriction, and what we're finding is that it's not trivial to do - we're constantly running into these "it causes the kernel to stop booting on X" bugs, or worse "fixing X causes plaforms Y to work but causes platforms Z to break." Maybe we should just stop trying, and instead go back to the old requirement of requiring banks of memory aligned to a section, and be done with it. In any case, to call this a "latent bug" is incorrect - we've merely been trying so far _unsuccessfully_ to extend the ARM MM layer to accept something that it's never accepted before. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net.