linux-kernel - Re: [PATCH] mm/hmm.c : Remove additional check for lockdep_assert

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Message-Id: <20200312195850.29693d4e55ec27ae11443c0f@linux-foundation.org>
Date:   Thu, 12 Mar 2020 19:58:50 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     jglisse@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hmm.c : Remove additional check for
 lockdep_assert_held()

On Fri, 13 Mar 2020 07:41:00 +0530 Souptick Joarder <jrdr.linux@...il.com> wrote:

> walk_page_range() already has a check for lockdep_assert_held().
> So additional check for lockdep_assert_held() can be removed from
> hmm_range_fault().
> 
> ...
>
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -681,7 +681,6 @@ long hmm_range_fault(struct hmm_range *range, unsigned int flags)
>  	struct mm_struct *mm = range->notifier->mm;
>  	int ret;
>  
> -	lockdep_assert_held(&mm->mmap_sem);
>  
>  	do {
>  		/* If range is no longer valid force retry. */

It isn't very obvious that hmm_range_fault() is and will only be called
from walk_page_range() (is it?)