linux-kernel - Re: [RFC PATCH 5 1/7] kmod - add workqueue service thread store

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Date:	Tue, 07 Apr 2015 08:42:35 +0800
From:	Ian Kent <raven@...maw.net>
To:	David Howells <dhowells@...hat.com>
Cc:	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <onestero@...hat.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Benjamin Coddington <bcodding@...hat.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Jeff Layton <jeff.layton@...marydata.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC PATCH 5 1/7] kmod - add workqueue service thread store

On Thu, 2015-04-02 at 13:43 +0100, David Howells wrote:
> Ian Kent <raven@...maw.net> wrote:
> 
> > +static struct umh_wq_entry *umh_wq_find_entry(int token)
> > +{
> > +	struct umh_wq_entry *this, *entry;
> > +	struct hlist_head *bucket;
> > +	unsigned int hash;
> > +
> > +	hash = hash_32((unsigned long) token, UMH_WQ_HASH_SHIFT);
> > +	bucket = &umh_wq_hash[hash];
> > +
> > +	entry = ERR_PTR(-ENOENT);
> > +	if (hlist_empty(bucket))
> > +		goto out;
> > +
> > +	hlist_for_each_entry(this, bucket, umh_wq_hlist) {
> > +		if (this->token == token) {
> > +			entry = this;
> > +			break;
> > +		}
> > +	}
> > +out:
> > +	return entry;
> > +}
> 
> Can "struct umh_wq_entry *" be used as the token?

Probably not, for example.

Couldn't a user set a different workqueue_struct and have it used for
execution. Not sure what that would get the user but it sounds like the
original reason we couldn't allow execution directly within the caller
environment.

> 
> David


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