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Subject[PATCH 5.15 174/247] drivers: staging: rtl8192u: Fix deadlock in ieee80211_beacons_stop()
Date
From: Duoming Zhou <duoming@zju.edu.cn>

[ Upstream commit 806c7b53414934ba2a39449b31fd1a038e500273 ]

There is a deadlock in ieee80211_beacons_stop(), which is shown below:

(Thread 1) | (Thread 2)
| ieee80211_send_beacon()
ieee80211_beacons_stop() | mod_timer()
spin_lock_irqsave() //(1) | (wait a time)
... | ieee80211_send_beacon_cb()
del_timer_sync() | spin_lock_irqsave() //(2)
(wait timer to stop) | ...

We hold ieee->beacon_lock in position (1) of thread 1 and use
del_timer_sync() to wait timer to stop, but timer handler
also need ieee->beacon_lock in position (2) of thread 2.
As a result, ieee80211_beacons_stop() will block forever.

This patch extracts del_timer_sync() from the protection of
spin_lock_irqsave(), which could let timer handler to obtain
the needed lock.

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20220417135407.109536-1-duoming@zju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c b/drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c
index 1a193f900779..2b06706a7071 100644
--- a/drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c
+++ b/drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c
@@ -528,9 +528,9 @@ static void ieee80211_beacons_stop(struct ieee80211_device *ieee)
spin_lock_irqsave(&ieee->beacon_lock, flags);

ieee->beacon_txing = 0;
- del_timer_sync(&ieee->beacon_timer);

spin_unlock_irqrestore(&ieee->beacon_lock, flags);
+ del_timer_sync(&ieee->beacon_timer);
}

void ieee80211_stop_send_beacons(struct ieee80211_device *ieee)
--
2.35.1


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