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Date:   Tue, 20 Jun 2023 10:43:14 +0100
From:   Will Deacon <will@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        catalin.marinas@arm.com
Subject: Re: linux-next: manual merge of the mm tree with Linus' tree
Message-ID: <20230620094314.GA14607@willie-the-truck>
References: <20230619092355.133c5cdb@canb.auug.org.au>
 <20230619204309.GA13937@willie-the-truck>
 <20230619143944.fb445cb3f28bb839942ed4ae@linux-foundation.org>
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On Mon, Jun 19, 2023 at 02:39:44PM -0700, Andrew Morton wrote:
> On Mon, 19 Jun 2023 21:43:11 +0100 Will Deacon <will@kernel.org> wrote:
> 
> > >   	/*
> > >   	 * Do not downgrade mmap_lock if we are next to VM_GROWSDOWN or
> > >   	 * VM_GROWSUP VMA. Such VMAs can change their size under
> > 
> > This resolution seems to be causing horrible problems on arm64 with 16k
> > pages. I see things like the crash below, but the two branches being merged
> > are fine on their own.
> 
> I've dropped the mm.git side of this conflict so next -next should
> be better.

Thanks, Andrew. next-20230620 is still broken, so I came up with the diff
below in the meantime which seems to resolve the crashes. I don't pretend
to understand the VMA iterator stuff well enough though, so I may have
missed something else.

Will

--->8

diff --git a/mm/mmap.c b/mm/mmap.c
index 9a93b054148a..4c82e9b36fb3 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2396,6 +2396,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
                        if (error)
                                goto end_split_failed;
                }
+               mas_set(&mas_detach, count);
                vma_start_write(next);
                if (mas_store_gfp(&mas_detach, next, GFP_KERNEL))
                        goto munmap_gather_failed;