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Message-ID: <b18c8067-6709-6589-b52a-0e38150fa322@huawei.com>
Date: Thu, 17 Feb 2022 21:44:13 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Matthew Wilcox <willy@...radead.org>
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 2022/2/17 21:32, Matthew Wilcox wrote:
> 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.
>
>From this point of view, this helper would disturb the understanding of the code.
Many thanks for pointing this out. Sorry for my mindlessness.
>> }
>>
>> 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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