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authorBob Copeland <me@bobcopeland.com>2014-06-04 09:27:31 -0400
committerJohannes Berg <johannes.berg@intel.com>2014-06-23 11:05:27 +0200
commit2b470c39e895dfde5413b0a85fac928a353de48d (patch)
tree9f890c8927fbfb4bae1e252b77caace4793f008d
parent5ac2e35030113ed881ce9ad413d80f13ffe5b5a0 (diff)
downloadlinux-2b470c39e895dfde5413b0a85fac928a353de48d.tar.bz2
mac80211: remove ignore_plink_timer flag
The mesh_plink code is doing some interesting things with the ignore_plink_timer flag. It seems the original intent was to handle this race: cpu 0 cpu 1 ----- ----- start timer handler for state X acquire sta_lock change state from X to Y mod_timer() / del_timer() release sta_lock acquire sta_lock execute state Y timer too soon However, using the mod_timer()/del_timer() return values to detect these cases is broken. As a result, timers get ignored unnecessarily, and stations can get stuck in the peering state machine. Instead, we can detect the case by looking at the timer expiration. In the case of del_timer, just ignore the timers in the following (LISTEN/ESTAB) states since they won't have timers anyway. Signed-off-by: Bob Copeland <me@bobcopeland.com> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
-rw-r--r--net/mac80211/mesh_plink.c30
-rw-r--r--net/mac80211/sta_info.h2
2 files changed, 23 insertions, 9 deletions
diff --git a/net/mac80211/mesh_plink.c b/net/mac80211/mesh_plink.c
index e8f60aa2e848..63b874101b27 100644
--- a/net/mac80211/mesh_plink.c
+++ b/net/mac80211/mesh_plink.c
@@ -551,11 +551,30 @@ static void mesh_plink_timer(unsigned long data)
return;
spin_lock_bh(&sta->lock);
- if (sta->ignore_plink_timer) {
- sta->ignore_plink_timer = false;
+
+ /* If a timer fires just before a state transition on another CPU,
+ * we may have already extended the timeout and changed state by the
+ * time we've acquired the lock and arrived here. In that case,
+ * skip this timer and wait for the new one.
+ */
+ if (time_before(jiffies, sta->plink_timer.expires)) {
+ mpl_dbg(sta->sdata,
+ "Ignoring timer for %pM in state %s (timer adjusted)",
+ sta->sta.addr, mplstates[sta->plink_state]);
spin_unlock_bh(&sta->lock);
return;
}
+
+ /* del_timer() and handler may race when entering these states */
+ if (sta->plink_state == NL80211_PLINK_LISTEN ||
+ sta->plink_state == NL80211_PLINK_ESTAB) {
+ mpl_dbg(sta->sdata,
+ "Ignoring timer for %pM in state %s (timer deleted)",
+ sta->sta.addr, mplstates[sta->plink_state]);
+ spin_unlock_bh(&sta->lock);
+ return;
+ }
+
mpl_dbg(sta->sdata,
"Mesh plink timer for %pM fired on state %s\n",
sta->sta.addr, mplstates[sta->plink_state]);
@@ -773,9 +792,7 @@ static u32 mesh_plink_fsm(struct ieee80211_sub_if_data *sdata,
break;
case CNF_ACPT:
sta->plink_state = NL80211_PLINK_CNF_RCVD;
- if (!mod_plink_timer(sta,
- mshcfg->dot11MeshConfirmTimeout))
- sta->ignore_plink_timer = true;
+ mod_plink_timer(sta, mshcfg->dot11MeshConfirmTimeout);
break;
default:
break;
@@ -834,8 +851,7 @@ static u32 mesh_plink_fsm(struct ieee80211_sub_if_data *sdata,
case NL80211_PLINK_HOLDING:
switch (event) {
case CLS_ACPT:
- if (del_timer(&sta->plink_timer))
- sta->ignore_plink_timer = 1;
+ del_timer(&sta->plink_timer);
mesh_plink_fsm_restart(sta);
break;
case OPN_ACPT:
diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
index dee0b645b34c..159cac903ce8 100644
--- a/net/mac80211/sta_info.h
+++ b/net/mac80211/sta_info.h
@@ -306,7 +306,6 @@ struct ieee80211_tx_latency_stat {
* @plid: Peer link ID
* @reason: Cancel reason on PLINK_HOLDING state
* @plink_retries: Retries in establishment
- * @ignore_plink_timer: ignore the peer-link timer (used internally)
* @plink_state: peer link state
* @plink_timeout: timeout of peer link
* @plink_timer: peer link watch timer
@@ -421,7 +420,6 @@ struct sta_info {
u16 plid;
u16 reason;
u8 plink_retries;
- bool ignore_plink_timer;
enum nl80211_plink_state plink_state;
u32 plink_timeout;
struct timer_list plink_timer;