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Message-ID: <Yg5OaP+4hclrUcB9@casper.infradead.org>
Date: Thu, 17 Feb 2022 13:32:24 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Miaohe Lin <linmiaohe@...wei.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mmu_notifiers: use helper function
mmu_notifier_synchronize()
On Thu, Feb 17, 2022 at 07:09:48PM +0800, Miaohe Lin wrote:
> Use helper function mmu_notifier_synchronize() to ensure all mmu_notifiers
> are freed. Minor readability improvement.
Is it though?
> @@ -334,15 +334,15 @@ static void mn_hlist_release(struct mmu_notifier_subscriptions *subscriptions,
> srcu_read_unlock(&srcu, id);
>
> /*
> - * synchronize_srcu here prevents mmu_notifier_release from returning to
> - * exit_mmap (which would proceed with freeing all pages in the mm)
> - * until the ->release method returns, if it was invoked by
> - * mmu_notifier_unregister.
> + * mmu_notifier_synchronize here prevents mmu_notifier_release from
> + * returning to exit_mmap (which would proceed with freeing all pages
> + * in the mm) until the ->release method returns, if it was invoked
> + * by mmu_notifier_unregister.
> *
> * The notifier_subscriptions can't go away from under us because
> * one mm_count is held by exit_mmap.
> */
> - synchronize_srcu(&srcu);
> + mmu_notifier_synchronize();
We just read_unlocked the &srcu. Now I have to jump to the definition
of mmu_notifier_synchronize() to find out that it's now waiting for the
very same srcu. I think this abstraction makes the code harder to read,
not easier.
> }
>
> void __mmu_notifier_release(struct mm_struct *mm)
> @@ -851,7 +851,7 @@ void mmu_notifier_unregister(struct mmu_notifier *subscription,
> * Wait for any running method to finish, of course including
> * ->release if it was run by mmu_notifier_release instead of us.
> */
> - synchronize_srcu(&srcu);
> + mmu_notifier_synchronize();
Same here.
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