linux-kernel - Re: [PATCH] arm64: Track no early_pgtable

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Date:   Fri, 5 Nov 2021 10:08:05 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     Mike Rapoport <rppt@...nel.org>, Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: Track no early_pgtable_alloc() for kmemleak

On Thu, Nov 04, 2021 at 01:57:03PM -0400, Qian Cai wrote:
> On 11/4/21 1:06 PM, Mike Rapoport wrote:
> > I think I'll be better to rename MEMBLOCK_ALLOC_KASAN to, say,
> > MEMBLOCK_ALLOC_NOKMEMLEAK and use that for both KASAN and page table cases.
> 
> Okay, that would look a bit nicer.

Or MEMBLOCK_ALLOC_ACCESSIBLE_NOLEAKTRACE to match SLAB_NOLEAKTRACE and
also hint that it's accessible memory.

> > But more generally, we are going to hit this again and again.
> > Couldn't we add a memblock allocation as a mean to get more memory to
> > kmemleak::mem_pool_alloc()?
> 
> For the last 5 years, this is the second time I am ware of this kind of
> issue just because of the 64KB->4KB switch on those servers, although I
> agree it could happen again in the future due to some new debugging
> features etc. I don't feel a strong need to rewrite it now though. Not
> sure if Catalin saw things differently. Anyway, Mike, do you agree that
> we could rewrite that separately in the future?

I was talking to Mike on IRC last night and I think you still need a
flag, otherwise you could get a recursive memblock -> kmemleak ->
memblock call (that's why we have SLAB_NOLEAKTRACE). So for the time
being, a new MEMBLOCK_* definition would do.

I wonder whether we could actually use the bottom bits in the end/limit
as actual flags so one can do (MEMBLOCK_ALLOC_ACCESSIBLE |
MEMBLOCK_NOLEAKTRACE). But that could be for a separate clean-up.

-- 
Catalin