linux-kernel - Re: [PATCH 1/2] mmu_notifiers: Restore documentation for .invalidate

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Message-ID: <20230524114859.000016e3.zhi.wang.linux@gmail.com>
Date:   Wed, 24 May 2023 11:48:59 +0800
From:   Zhi Wang <zhi.wang.linux@...il.com>
To:     Alistair Popple <apopple@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, will@...nel.org,
        catalin.marinas@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, robin.murphy@....com,
        nicolinc@...dia.com, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, jgg@...dia.com,
        John Hubbard <jhubbard@...dia.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH 1/2] mmu_notifiers: Restore documentation for
 .invalidate_range()

On Wed, 24 May 2023 11:47:28 +1000
Alistair Popple <apopple@...dia.com> wrote:

It is actually commit 4e15a073a168 ("Revert "mm, mmu_notifier:
annotate mmu notifiers with blockable invalidate callbacks"")'s problem.
It tries to revert commit 5ff7091f5a2c but forgets to get back this
piece of comment.

It would be better to have a Fixes tag in the commit message.

> The .invalidate_range() callback is called by
> mmu_notifier_invalidate_range() which is often called while holding
> the ptl spin-lock. Therefore any implementations of this callback must
> not sleep. This was originally documented when the call back was added
> in commit 0f0a327fa12c ("mmu_notifier: add the callback for
> mmu_notifier_invalidate_range()") but appears to have been
> inadvertently removed by commit 5ff7091f5a2c ("mm, mmu_notifier:
> annotate mmu notifiers with blockable invalidate callbacks").
> 
> Restore the comment to make it clear that .invalidate_range()
> callbacks may not sleep.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> ---
>  include/linux/mmu_notifier.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> index 64a3e05..447d757 100644
> --- a/include/linux/mmu_notifier.h
> +++ b/include/linux/mmu_notifier.h
> @@ -200,6 +200,9 @@ struct mmu_notifier_ops {
>  	 * external TLB range needs to be flushed. For more in depth
>  	 * discussion on this see Documentation/mm/mmu_notifier.rst
>  	 *
> +	 * The invalidate_range() function is called under the ptl
> +	 * spin-lock and not allowed to sleep.
> +	 *
>  	 * Note that this function might be called with just a sub-range
>  	 * of what was passed to invalidate_range_start()/end(), if
>  	 * called between those functions.
> 
> base-commit: 44c026a73be8038f03dbdeef028b642880cf1511