linux-kernel - Re: [PATCH v13 57/70] mm/mlock: use vma iterator and maple state instead of vma linked list

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Message-ID: <20220825132054.ymenz4cewiemsxw7@revolver>
Date:   Thu, 25 Aug 2022 13:21:01 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Mark Brown <broonie@...nel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v13 57/70] mm/mlock: use vma iterator and maple state
 instead of vma linked list

* Mark Brown <broonie@...nel.org> [220824 20:34]:
> On Mon, Aug 22, 2022 at 03:06:30PM +0000, Liam Howlett wrote:
> > From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> > 
> > Handle overflow checking in count_mm_mlocked_page_nr() differently.
> 
> Our QA team found that since next-20220823 we're seeing a couple of test
> failures in the check_mmap_options kselftest on arm64 platforms with MTE
> that aren't present in mainline:
> 
> # # FAIL: mprotect not ignoring clear PROT_MTE property
> # not ok 21 Check clear PROT_MTE flags with private mapping, sync error mode and mmap memory
> # # FAIL: mprotect not ignoring clear PROT_MTE property
> # not ok 22 Check clear PROT_MTE flags with private mapping and sync error mode and mmap/mprotect memory

Thanks.

> 
> I bisected this using qemu[1] which landed on 4ceb4bca479d41a
> ("mm/mprotect: use maple tree navigation instead of vma linked list"),
> though I'm not 100% sure I trust the specific identification of the
> commit I'm pretty confident it's at the very least in this series.  I've
> not done any analysis of the failure beyond getting this bisect result.
> 
> [1] qemu -smp cpus=4 -cpu max -machine virt,gic-version=3,mte=on

This helps a lot.  I think your bisect is accurate:

...
        struct mmu_gather tlb;
+       MA_STATE(mas, &current->mm->mm_mt, start, start);
 
        start = untagged_addr(start);
...

It looks like I search against the tagged address.  I should initialize
the state to 0 and mas_set(&mas, start) after untagging the address.

I'll send out a patch once I have recreated and verified this is the
issue.

Cheers,
Liam