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Commit 0fdc2678 authored by Jeff Layton's avatar Jeff Layton Committed by J. Bruce Fields
Browse files

sunrpc: get rid of use_gssp_lock 



We can achieve the same result with a cmpxchg(). This also fixes a
potential race in use_gss_proxy(). The value of sn->use_gss_proxy could
go from -1 to 1 just after we check it in use_gss_proxy() but before we
acquire the spinlock. The procfile write would end up returning success
but the value would flip to 0 soon afterward. With this method we not
only avoid locking but the first "setter" always wins.

Signed-off-by: default avatarJeff Layton <jlayton@redhat.com>
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent a92e5eb1

net/sunrpc/auth_gss/svcauth_gss.c

+18 −24
Original line number Diff line number Diff line
@@ -1263,41 +1263,35 @@ static int svcauth_gss_proxy_init(struct svc_rqst *rqstp, 
	return ret;

}



DEFINE_SPINLOCK(use_gssp_lock);



static bool use_gss_proxy(struct net *net)

/*

 * Try to set the sn->use_gss_proxy variable to a new value. We only allow

 * it to be changed if it's currently undefined (-1). If it's any other value

 * then return -EBUSY unless the type wouldn't have changed anyway.

 */

static int set_gss_proxy(struct net *net, int type)

{

	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);

	int ret;



	if (sn->use_gss_proxy != -1)

		return sn->use_gss_proxy;

	spin_lock(&use_gssp_lock);

	/*

	 * If you wanted gss-proxy, you should have said so before

	 * starting to accept requests:

	 */

	sn->use_gss_proxy = 0;

	spin_unlock(&use_gssp_lock);

	WARN_ON_ONCE(type != 0 && type != 1);

	ret = cmpxchg(&sn->use_gss_proxy, -1, type);

	if (ret != -1 && ret != type)

		return -EBUSY;

	return 0;

}



#ifdef CONFIG_PROC_FS



static int set_gss_proxy(struct net *net, int type)

static bool use_gss_proxy(struct net *net)

{

	struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);

	int ret = 0;



	WARN_ON_ONCE(type != 0 && type != 1);

	spin_lock(&use_gssp_lock);

	if (sn->use_gss_proxy == -1 || sn->use_gss_proxy == type)

		sn->use_gss_proxy = type;

	else

		ret = -EBUSY;

	spin_unlock(&use_gssp_lock);

	return ret;

	/* If use_gss_proxy is still undefined, then try to disable it */

	if (sn->use_gss_proxy == -1)

		set_gss_proxy(net, 0);

	return sn->use_gss_proxy;

}



#ifdef CONFIG_PROC_FS



static ssize_t write_gssp(struct file *file, const char __user *buf,

			 size_t count, loff_t *ppos)

{