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@xxxxxxxxxxxxxxxxxxx>
---
drivers/net/wireless/mwifiex/main.h | 1 -
drivers/net/wireless/mwifiex/wmm.c | 13 ++++++-------
2 files changed, 6 insertions(+), 8 deletions(-)
diff --git a/drivers/net/wireless/mwifiex/main.h b/drivers/net/wireless/mwifiex/main.h
index d94406a..082a468 100644
--- a/drivers/net/wireless/mwifiex/main.h
+++ b/drivers/net/wireless/mwifiex/main.h
@@ -216,7 +216,6 @@ 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 96eed2f..62b07d3 100644
--- a/drivers/net/wireless/mwifiex/wmm.c
+++ b/drivers/net/wireless/mwifiex/wmm.c
@@ -919,8 +919,12 @@ 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.
@@ -979,12 +983,7 @@ 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,
--
1.7.10.4
--
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