4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gao Feng <gfree.w...@vip.163.com>


[ Upstream commit e5dadc65f9e0177eb649bcd9d333f1ebf871223e ]

The global percpu variable ppp_xmit_recursion is used to detect the ppp
xmit recursion to avoid the deadlock, which is caused by one CPU tries to
lock the xmit lock twice. But it would report false recursion when one CPU
wants to send the skb from two different PPP devices, like one L2TP on the
PPPoE. It is a normal case actually.

Now use one percpu member of struct ppp instead of the gloable variable to
detect the xmit recursion of one ppp device.

Fixes: 55454a565836 ("ppp: avoid dealock on recursive xmit")
Signed-off-by: Gao Feng <gfree.w...@vip.163.com>
Signed-off-by: Liu Jianying <jianying....@ikuai8.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/net/ppp/ppp_generic.c |   30 +++++++++++++++++++++---------
 1 file changed, 21 insertions(+), 9 deletions(-)

--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -119,6 +119,7 @@ struct ppp {
        int             n_channels;     /* how many channels are attached 54 */
        spinlock_t      rlock;          /* lock for receive side 58 */
        spinlock_t      wlock;          /* lock for transmit side 5c */
+       int             *xmit_recursion __percpu; /* xmit recursion detect */
        int             mru;            /* max receive unit 60 */
        unsigned int    flags;          /* control bits 64 */
        unsigned int    xstate;         /* transmit state bits 68 */
@@ -1024,6 +1025,7 @@ static int ppp_dev_configure(struct net
        struct ppp *ppp = netdev_priv(dev);
        int indx;
        int err;
+       int cpu;
 
        ppp->dev = dev;
        ppp->ppp_net = src_net;
@@ -1038,6 +1040,15 @@ static int ppp_dev_configure(struct net
        INIT_LIST_HEAD(&ppp->channels);
        spin_lock_init(&ppp->rlock);
        spin_lock_init(&ppp->wlock);
+
+       ppp->xmit_recursion = alloc_percpu(int);
+       if (!ppp->xmit_recursion) {
+               err = -ENOMEM;
+               goto err1;
+       }
+       for_each_possible_cpu(cpu)
+               (*per_cpu_ptr(ppp->xmit_recursion, cpu)) = 0;
+
 #ifdef CONFIG_PPP_MULTILINK
        ppp->minseq = -1;
        skb_queue_head_init(&ppp->mrq);
@@ -1049,11 +1060,15 @@ static int ppp_dev_configure(struct net
 
        err = ppp_unit_register(ppp, conf->unit, conf->ifname_is_set);
        if (err < 0)
-               return err;
+               goto err2;
 
        conf->file->private_data = &ppp->file;
 
        return 0;
+err2:
+       free_percpu(ppp->xmit_recursion);
+err1:
+       return err;
 }
 
 static const struct nla_policy ppp_nl_policy[IFLA_PPP_MAX + 1] = {
@@ -1399,18 +1414,16 @@ static void __ppp_xmit_process(struct pp
        ppp_xmit_unlock(ppp);
 }
 
-static DEFINE_PER_CPU(int, ppp_xmit_recursion);
-
 static void ppp_xmit_process(struct ppp *ppp)
 {
        local_bh_disable();
 
-       if (unlikely(__this_cpu_read(ppp_xmit_recursion)))
+       if (unlikely(*this_cpu_ptr(ppp->xmit_recursion)))
                goto err;
 
-       __this_cpu_inc(ppp_xmit_recursion);
+       (*this_cpu_ptr(ppp->xmit_recursion))++;
        __ppp_xmit_process(ppp);
-       __this_cpu_dec(ppp_xmit_recursion);
+       (*this_cpu_ptr(ppp->xmit_recursion))--;
 
        local_bh_enable();
 
@@ -1904,7 +1917,7 @@ static void __ppp_channel_push(struct ch
                read_lock_bh(&pch->upl);
                ppp = pch->ppp;
                if (ppp)
-                       __ppp_xmit_process(ppp);
+                       ppp_xmit_process(ppp);
                read_unlock_bh(&pch->upl);
        }
 }
@@ -1913,9 +1926,7 @@ static void ppp_channel_push(struct chan
 {
        local_bh_disable();
 
-       __this_cpu_inc(ppp_xmit_recursion);
        __ppp_channel_push(pch);
-       __this_cpu_dec(ppp_xmit_recursion);
 
        local_bh_enable();
 }
@@ -3056,6 +3067,7 @@ static void ppp_destroy_interface(struct
 #endif /* CONFIG_PPP_FILTER */
 
        kfree_skb(ppp->xmit_pending);
+       free_percpu(ppp->xmit_recursion);
 
        free_netdev(ppp->dev);
 }


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