linux-kernel - Re: [PATCH v2 2/2] efi: efi_mem_reserve(): don't reserve through memblock after mm

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Message-ID: <20170109133152.2izkcrzgzinxdwux@techsingularity.net>
Date:   Mon, 9 Jan 2017 13:31:52 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     Dave Young <dyoung@...hat.com>,
        Nicolai Stange <nicstange@...il.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH v2 2/2] efi: efi_mem_reserve(): don't reserve through
 memblock after mm_init()

On Mon, Jan 09, 2017 at 11:44:00AM +0000, Matt Fleming wrote:
> On Thu, 05 Jan, at 05:12:42PM, Dave Young wrote:
> > On 12/22/16 at 11:23am, Nicolai Stange wrote:
> > > Before invoking the arch specific handler, efi_mem_reserve() reserves
> > > the given memory region through memblock.
> > > 
> > > efi_mem_reserve() can get called after mm_init() though -- through
> > > efi_bgrt_init(), for example. After mm_init(), memblock is dead and should
> > > not be used anymore.
> > 
> > It did not fail during previous test so we did not catch this bug, if memblock
> > can not be used after mm_init(), IMHO it should fail instead of silently succeed.
>  
> This must literally be the fifth time or so that I've been caught out
> by this over the years because there's no hard error if you call the
> memblock code after slab and co. are up.
> 
> MM folks, is there some way to catch these errors without requiring
> the sprinkling of slab_is_available() everywhere?
> 

Well, you could put in a __init global variable about availability into
mm/memblock.c and then check it in memblock APIs like memblock_reserve()
to BUG_ON? I know BUG_ON is frowned upon but this is not likely to be a
situation that can be sensibly recovered.

-- 
Mel Gorman
SUSE Labs