Re: [PATCH -next] NFSD: Use DEFINE_SPINLOCK() for spinlock

From: Bruce Fields <bfields@fieldses.org>
To: Chuck Lever III <chuck.lever@oracle.com>
Cc: Huang Guobin <huangguobin4@huawei.com>,
	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
Date: Tue, 6 Apr 2021 11:55:15 -0400	[thread overview]
Message-ID: <20210406155515.GA21267@fieldses.org> (raw)
In-Reply-To: <5B67E76D-139B-4004-9DE0-A626026CAEB1@oracle.com>

On Tue, Apr 06, 2021 at 03:46:34PM +0000, Chuck Lever III wrote:
> 
> 
> > On Apr 6, 2021, at 8:08 AM, Huang Guobin <huangguobin4@huawei.com> wrote:
> > 
> > From: Guobin Huang <huangguobin4@huawei.com>
> > 
> > spinlock can be initialized automatically with DEFINE_SPINLOCK()
> > rather than explicitly calling spin_lock_init().
> > 
> > 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-huangguobin4@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?

The other nfsd_drc_lock users run in nfsd threads, which shouldn't be
running yet at the point we call set_max_drc.

Reinitializing the lock each time is pretty weird, though, ACK to the
patch even if it's just cleanup.

--b.

> 
> 
> > ---
> > fs/nfsd/nfssvc.c | 3 +--
> > 1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > 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;
> > 
> > @@ -563,7 +563,6 @@ static void set_max_drc(void)
> > 	nfsd_drc_max_mem = (nr_free_buffer_pages()
> > 					>> NFSD_DRC_SIZE_SHIFT) * PAGE_SIZE;
> > 	nfsd_drc_mem_used = 0;
> > -	spin_lock_init(&nfsd_drc_lock);
> > 	dprintk("%s nfsd_drc_max_mem %lu \n", __func__, nfsd_drc_max_mem);
> > }
> > 
> > 
> 
> --
> Chuck Lever
> 
> 