linux-kernel - Re: [PATCH 7/8] mmap locking API: add MMAP_LOCK

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Message-Id: <1c463464-1d72-287e-e785-f077a95ccf20@linux.ibm.com>
Date:   Mon, 6 Apr 2020 11:46:27 +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>
Subject: Re: [PATCH 7/8] mmap locking API: add MMAP_LOCK_INITIALIZER

Le 26/03/2020 à 08:02, Michel Lespinasse a écrit :
> Define a new initializer for the mmap locking api.
> Initially this just evaluates to __RWSEM_INITIALIZER as the API
> is defined as wrappers around rwsem.

I can't see the benefit of this change.
The overall idea is to hide the mmap_sem name. Here the macro 
MMAP_LOCK_INITIALIZER() doesn't hide the name.

I think we can keep that in place until the real change of the mmap_sem to 
something else.

Cheers,
Laurent.

> 
> Signed-off-by: Michel Lespinasse <walken@...gle.com>
> ---
>   arch/x86/kernel/tboot.c    | 2 +-
>   drivers/firmware/efi/efi.c | 2 +-
>   include/linux/mmap_lock.h  | 2 ++
>   mm/init-mm.c               | 2 +-
>   4 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
> index b89f6ac6a0c0..4b79335624b1 100644
> --- a/arch/x86/kernel/tboot.c
> +++ b/arch/x86/kernel/tboot.c
> @@ -90,7 +90,7 @@ static struct mm_struct tboot_mm = {
>   	.pgd            = swapper_pg_dir,
>   	.mm_users       = ATOMIC_INIT(2),
>   	.mm_count       = ATOMIC_INIT(1),
> -	.mmap_sem       = __RWSEM_INITIALIZER(init_mm.mmap_sem),
> +	.mmap_sem       = MMAP_LOCK_INITIALIZER(init_mm.mmap_sem),
>   	.page_table_lock =  __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
>   	.mmlist         = LIST_HEAD_INIT(init_mm.mmlist),
>   };
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 21ea99f65113..5bdfe698cd7f 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -60,7 +60,7 @@ struct mm_struct efi_mm = {
>   	.mm_rb			= RB_ROOT,
>   	.mm_users		= ATOMIC_INIT(2),
>   	.mm_count		= ATOMIC_INIT(1),
> -	.mmap_sem		= __RWSEM_INITIALIZER(efi_mm.mmap_sem),
> +	.mmap_sem		= MMAP_LOCK_INITIALIZER(efi_mm.mmap_sem),
>   	.page_table_lock	= __SPIN_LOCK_UNLOCKED(efi_mm.page_table_lock),
>   	.mmlist			= LIST_HEAD_INIT(efi_mm.mmlist),
>   	.cpu_bitmap		= { [BITS_TO_LONGS(NR_CPUS)] = 0},
> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 00d6cc02581d..7474b15bba38 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h
> @@ -1,6 +1,8 @@
>   #ifndef _LINUX_MMAP_LOCK_H
>   #define _LINUX_MMAP_LOCK_H
>   
> +#define MMAP_LOCK_INITIALIZER(name) __RWSEM_INITIALIZER(name)
> +
>   static inline void mmap_init_lock(struct mm_struct *mm)
>   {
>   	init_rwsem(&mm->mmap_sem);
> diff --git a/mm/init-mm.c b/mm/init-mm.c
> index 19603302a77f..3c128bd6a30c 100644
> --- a/mm/init-mm.c
> +++ b/mm/init-mm.c
> @@ -31,7 +31,7 @@ struct mm_struct init_mm = {
>   	.pgd		= swapper_pg_dir,
>   	.mm_users	= ATOMIC_INIT(2),
>   	.mm_count	= ATOMIC_INIT(1),
> -	.mmap_sem	= __RWSEM_INITIALIZER(init_mm.mmap_sem),
> +	.mmap_sem	= MMAP_LOCK_INITIALIZER(init_mm.mmap_sem),
>   	.page_table_lock =  __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
>   	.arg_lock	=  __SPIN_LOCK_UNLOCKED(init_mm.arg_lock),
>   	.mmlist		= LIST_HEAD_INIT(init_mm.mmlist),
>