[PATCH 1/1] mac80211: only single mutex locked to prevent deadlock

[PATCH 1/1] mac80211: only single mutex locked to prevent deadlock

[wey-yi.w.guy]

From: Wey-Yi Guy <wey-yi.w.guy@intel.com>

Both ifmgd->mtx and sdata->local->iflist_mtx are locked in
ieee80211_mgd_probe_ap(), not sure it will cause deadlock condition. but
it is better to only has one mutex at a time.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
---
 net/mac80211/mlme.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 1e1d16c..e23df14 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -914,10 +914,13 @@ static void ieee80211_mgd_probe_ap(struct ieee80211_sub_if_data *sdata,
 	if (already)
 		goto out;
 
+	mutex_unlock(&ifmgd->mtx);
+
 	mutex_lock(&sdata->local->iflist_mtx);
 	ieee80211_recalc_ps(sdata->local, -1);
 	mutex_unlock(&sdata->local->iflist_mtx);
 
+	mutex_lock(&ifmgd->mtx);
 	ifmgd->probe_send_count = 0;
 	ieee80211_mgd_probe_ap_send(sdata);
  out:
-- 
1.5.6.3

Re: [PATCH 1/1] mac80211: only single mutex locked to prevent deadlock

[Johannes Berg]

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On Mon, 2010-01-25 at 10:12 -0800, wey-yi.w.guy@intel.com wrote:
> From: Wey-Yi Guy <wey-yi.w.guy@intel.com>
> 
> Both ifmgd->mtx and sdata->local->iflist_mtx are locked in
> ieee80211_mgd_probe_ap(), not sure it will cause deadlock condition. but
> it is better to only has one mutex at a time.

It shouldn't cause a deadlock, we do this all the time, e.g. in
ieee80211_rx_mgmt_probe_resp(), so I don't think the extra locking makes
a lot of sense.

johannes

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