mwifiex: fix infinite loop by removing NO_PKT_PRIO_TID

Using NO_PKT_PRIO_TID and tx_pkts_queued to check for an empty
state, can lead to a contradictory state, resulting in an
infinite loop. Currently queueing and dequeuing of packets is
not synchronized, and can happen concurrently. While tx_pkts_queued
is incremented when adding a packet, max prio is set to NO_PKT when
the WMM list is empty. If a packet is added right after the check
for empty, but before setting max prio to NO_PKT, that packet is
trapped and creates an infinite loop.

Because of the new packet, tx_pkts_queued is at least 1, indicating
wmm lists are not empty. Opposing that max prio is NO_PKT, which
means "skip this wmm queue, it has no packets". The infinite loop
results, because the main loop checks the wmm lists for not empty
via tx_pkts_queued, but for dequeing it uses max_prio to see if it
can skip current list. This will never end, unless a new packet is
added which will restore max prio to the level of the trapped packet.

The solution here is to rely on tx_pkts_queued solely for checking
wmm queue to be empty, and drop the NO_PKT define. It does not
address the locking issue.

Signed-off-by: Andreas Fenkart <andreas.fenkart@streamunlimited.com>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --git a/drivers/net/wireless/mwifiex/main.h b/drivers/net/wireless/mwifiex/main.h
index 622b17f..b7484ef 100644 (file)
--- a/drivers/net/wireless/mwifiex/main.h
+++ b/drivers/net/wireless/mwifiex/main.h
@@ -219,7 +219,6 @@ struct mwifiex_tid_tbl {
 #define WMM_HIGHEST_PRIORITY           7
 #define HIGH_PRIO_TID                          7
 #define LOW_PRIO_TID                           0
-#define NO_PKT_PRIO_TID                                (-1)
 
 struct mwifiex_wmm_desc {
        struct mwifiex_tid_tbl tid_tbl_ptr[MAX_NUM_TID];

diff --git a/drivers/net/wireless/mwifiex/wmm.c b/drivers/net/wireless/mwifiex/wmm.c
index c1d8488..75c8e80 100644 (file)
--- a/drivers/net/wireless/mwifiex/wmm.c
+++ b/drivers/net/wireless/mwifiex/wmm.c
@@ -916,8 +916,12 @@ mwifiex_wmm_get_highest_priolist_ptr(struct mwifiex_adapter *adapter,
 
                do {
                        priv_tmp = bssprio_node->priv;
-                       hqp = &priv_tmp->wmm.highest_queued_prio;
 
+                       if (atomic_read(&priv_tmp->wmm.tx_pkts_queued) == 0)
+                               goto skip_bss;
+
+                       /* iterate over the WMM queues of the BSS */
+                       hqp = &priv_tmp->wmm.highest_queued_prio;
                        for (i = atomic_read(hqp); i >= LOW_PRIO_TID; --i) {
 
                                tid_ptr = &(priv_tmp)->wmm.
@@ -976,12 +980,7 @@ mwifiex_wmm_get_highest_priolist_ptr(struct mwifiex_adapter *adapter,
                                } while (ptr != head);
                        }
 
-                       /* No packet at any TID for this priv. Mark as such
-                        * to skip checking TIDs for this priv (until pkt is
-                        * added).
-                        */
-                       atomic_set(hqp, NO_PKT_PRIO_TID);
-
+skip_bss:
                        /* Get next bss priority node */
                        bssprio_node = list_first_entry(&bssprio_node->list,
                                                struct mwifiex_bss_prio_node,