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mwifiex: fix infinite loop by removing NO_PKT_PRIO_TID

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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>
This commit is contained in:
Andreas Fenkart 2013-04-04 20:03:52 -07:00 committed by John W. Linville
parent 6d2344ec60
commit 333f6b22c5
2 changed files with 6 additions and 8 deletions
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1
drivers/net/wireless/mwifiex/main.h
View file

@ -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];

13
drivers/net/wireless/mwifiex/wmm.c
View file

@ -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,