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From: Andrew Morton <>
To: Yang Shi <>
Subject: Re: [v3 PATCH] mm: mmu_gather: remove __tlb_reset_range() for force flush
Date: Tue, 21 May 2019 16:18:26 -0700
Message-ID: <> (raw)
In-Reply-To: <>

On Mon, 20 May 2019 11:17:32 +0800 Yang Shi <> wrote:

> A few new fields were added to mmu_gather to make TLB flush smarter for
> huge page by telling what level of page table is changed.
> __tlb_reset_range() is used to reset all these page table state to
> unchanged, which is called by TLB flush for parallel mapping changes for
> the same range under non-exclusive lock (i.e. read mmap_sem).  Before
> commit dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in
> munmap"), the syscalls (e.g. MADV_DONTNEED, MADV_FREE) which may update
> PTEs in parallel don't remove page tables.  But, the forementioned
> commit may do munmap() under read mmap_sem and free page tables.  This
> may result in program hang on aarch64 reported by Jan Stancek.  The
> problem could be reproduced by his test program with slightly modified
> below.
> ...
> Use fullmm flush since it yields much better performance on aarch64 and
> non-fullmm doesn't yields significant difference on x86.
> The original proposed fix came from Jan Stancek who mainly debugged this
> issue, I just wrapped up everything together.

Thanks.  I'll add

Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap")

to this.

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Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20  3:17 Yang Shi
2019-05-21 23:18 ` Andrew Morton [this message]
2019-05-22  1:00   ` Yang Shi

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