From: Dave Hansen <dave@sr71.net>
To: Jan Kara <jack@suse.cz>
Cc: viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com,
tim.c.chen@linux.intel.com, ak@linux.intel.com
Subject: Re: [RFC][PATCH 1/2] fs: use RCU for free_super() vs. __sb_start_write()
Date: Wed, 24 Jun 2015 13:21:26 -0700 [thread overview]
Message-ID: <558B1146.5050106@sr71.net> (raw)
In-Reply-To: <20150623110933.GE2427@quack.suse.cz>
On 06/23/2015 04:09 AM, Jan Kara wrote:
>> @@ -1340,7 +1344,7 @@ int freeze_super(struct super_block *sb)
>> printk(KERN_ERR
>> "VFS:Filesystem freeze failed\n");
>> sb->s_writers.frozen = SB_UNFROZEN;
>> - smp_wmb();
>> + synchronize_rcu();
>
> Do we really need synchronize_rcu() here? We just need to make sure write
> to sb->s_writers.frozen happens before we start waking processes...
I don't think it is necessary. We only need to be concerned in practice
if someone could be inside a critical section when we are executing
this. I *think* the only case that we have that really matters will be
taken care of by the _first_ synchronize_rcu().
It's definitely worth adding a comment.
prev parent reply other threads:[~2015-06-24 20:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-19 22:32 [RFC][PATCH 1/2] fs: use RCU for free_super() vs. __sb_start_write() Dave Hansen
2015-06-19 22:32 ` Dave Hansen
2015-06-19 22:32 ` [RFC][PATCH 2/2] fs: conditionally do memory barrier in __sb_end_write() Dave Hansen
2015-06-19 22:32 ` Dave Hansen
2015-06-23 12:02 ` Jan Kara
2015-06-23 11:09 ` [RFC][PATCH 1/2] fs: use RCU for free_super() vs. __sb_start_write() Jan Kara
2015-06-24 20:21 ` Dave Hansen [this message]
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