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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Huang Guobin <huangguobin4@huawei.com>,
        Bruce Fields <bfields@fieldses.org>
CC:     Jeff Layton <jlayton@poochiereds.net>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -next] NFSD: Use DEFINE_SPINLOCK() for spinlock
Thread-Topic: [PATCH -next] NFSD: Use DEFINE_SPINLOCK() for spinlock
Thread-Index: AQHXKt2V1gcSxm7bVkeOdiAjqSPoqaqnok6A
Date:   Tue, 6 Apr 2021 15:46:34 +0000
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References: <1617710898-49064-1-git-send-email-huangguobin4@huawei.com>
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> On Apr 6, 2021, at 8:08 AM, Huang Guobin <huangguobin4@huawei.com> wrote:
>=20
> From: Guobin Huang <huangguobin4@huawei.com>
>=20
> spinlock can be initialized automatically with DEFINE_SPINLOCK()
> rather than explicitly calling spin_lock_init().
>=20
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Signed-off-by: Guobin Huang <huangguobin4@huawei.com>

This same patch was sent last July, without the Reported-by:

https://lore.kernel.org/linux-nfs/1617710898-49064-1-git-send-email-huanggu=
obin4@huawei.com/T/#u

If I'm reading the code correctly, it appears that set_max_drc()
can be called more than once by user space API functions via
nfsd_create_serv().

It seems to me we want to guarantee that nfsd_drc_lock is
initialized exactly once, and using DEFINE_SPINLOCK() would
do just that.

Likewise, re-initializing nfsd_drc_mem_used is probably not good
to do either, but clobbering a spinlock like that might lead to
a crash.

Bruce, any further thoughts?


> ---
> fs/nfsd/nfssvc.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>=20
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index b2eef4112bc2..82ba034fa579 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -84,7 +84,7 @@ DEFINE_MUTEX(nfsd_mutex);
>  * version 4.1 DRC caches.
>  * nfsd_drc_pages_used tracks the current version 4.1 DRC memory usage.
>  */
> -spinlock_t	nfsd_drc_lock;
> +DEFINE_SPINLOCK(nfsd_drc_lock);
> unsigned long	nfsd_drc_max_mem;
> unsigned long	nfsd_drc_mem_used;
>=20
> @@ -563,7 +563,6 @@ static void set_max_drc(void)
> 	nfsd_drc_max_mem =3D (nr_free_buffer_pages()
> 					>> NFSD_DRC_SIZE_SHIFT) * PAGE_SIZE;
> 	nfsd_drc_mem_used =3D 0;
> -	spin_lock_init(&nfsd_drc_lock);
> 	dprintk("%s nfsd_drc_max_mem %lu \n", __func__, nfsd_drc_max_mem);
> }
>=20
>=20

--
Chuck Lever