linux-kernel - Re: [PATCH v5 06/10] mmap locking API: convert nested write lock sites

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Date:   Mon, 18 May 2020 15:24:29 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Michel Lespinasse <walken@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Liam Howlett <Liam.Howlett@...cle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        David Rientjes <rientjes@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, Ying Han <yinghan@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: Re: [PATCH v5 06/10] mmap locking API: convert nested write lock
 sites

Le 22/04/2020 à 02:14, Michel Lespinasse a écrit :
> Add API for nested write locks and convert the few call sites doing that.
> 
> Signed-off-by: Michel Lespinasse <walken@...gle.com>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>

Reviewed-by: Laurent Dufour <ldufour@...ux.ibm.com>

> ---
>   arch/um/include/asm/mmu_context.h | 3 ++-
>   include/linux/mmap_lock.h         | 5 +++++
>   kernel/fork.c                     | 2 +-
>   3 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h
> index 62262c5c7785..17ddd4edf875 100644
> --- a/arch/um/include/asm/mmu_context.h
> +++ b/arch/um/include/asm/mmu_context.h
> @@ -8,6 +8,7 @@
>   
>   #include <linux/sched.h>
>   #include <linux/mm_types.h>
> +#include <linux/mmap_lock.h>
>   
>   #include <asm/mmu.h>
>   
> @@ -47,7 +48,7 @@ static inline void activate_mm(struct mm_struct *old, struct mm_struct *new)
>   	 * when the new ->mm is used for the first time.
>   	 */
>   	__switch_mm(&new->context.id);
> -	down_write_nested(&new->mmap_sem, 1);
> +	mmap_write_lock_nested(new, SINGLE_DEPTH_NESTING);
>   	uml_setup_stubs(new);
>   	mmap_write_unlock(new);
>   }
> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 97ac53b66052..a757cb30ae77 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h
> @@ -11,6 +11,11 @@ static inline void mmap_write_lock(struct mm_struct *mm)
>   	down_write(&mm->mmap_sem);
>   }
>   
> +static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass)
> +{
> +	down_write_nested(&mm->mmap_sem, subclass);
> +}
> +
>   static inline int mmap_write_lock_killable(struct mm_struct *mm)
>   {
>   	return down_write_killable(&mm->mmap_sem);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 41d3f45c058e..a5d1d20ccba7 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -499,7 +499,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
>   	/*
>   	 * Not linked in yet - no deadlock potential:
>   	 */
> -	down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
> +	mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING);
>   
>   	/* No ordering required: file already has been exposed. */
>   	RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
>