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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: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Jeff Layton 2014-01-04 07:18:05 -05:00 committed by J. Bruce Fields
parent a92e5eb110
commit 0fdc26785d
1 changed files with 20 additions and 26 deletions
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46
net/sunrpc/auth_gss/svcauth_gss.c
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@ -1263,41 +1263,35 @@ out:
return ret;
}
DEFINE_SPINLOCK(use_gssp_lock);
/*
* 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;
WARN_ON_ONCE(type != 0 && type != 1);
ret = cmpxchg(&sn->use_gss_proxy, -1, type);
if (ret != -1 && ret != type)
return -EBUSY;
return 0;
}
static bool use_gss_proxy(struct net *net)
{
struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
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);
return 0;
/* 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 int set_gss_proxy(struct net *net, int type)
{
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;
}
static ssize_t write_gssp(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{