mac80211: fix race in ieee80211_register_hw()
A race condition leading to a kernel crash is observed during invocation of ieee80211_register_hw() on a dragonboard410c device having wcn36xx driver built as a loadable module along with a wifi manager in user-space waiting for a wifi device (wlanX) to be active. Sequence diagram for a particular kernel crash scenario: user-space ieee80211_register_hw() ieee80211_tasklet_handler() ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | | | |<---phy0----wiphy_register() | |-----iwd if_add---->| | | |<---IRQ----(RX packet) | Kernel crash | | due to unallocated | | workqueue. | | | | | alloc_ordered_workqueue() | | | | | Misc wiphy init. | | | | | ieee80211_if_add() | | | | As evident from above sequence diagram, this race condition isn't specific to a particular wifi driver but rather the initialization sequence in ieee80211_register_hw() needs to be fixed. So re-order the initialization sequence and the updated sequence diagram would look like: user-space ieee80211_register_hw() ieee80211_tasklet_handler() ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | | | | alloc_ordered_workqueue() | | | | | Misc wiphy init. | | | | |<---phy0----wiphy_register() | |-----iwd if_add---->| | | |<---IRQ----(RX packet) | | | | ieee80211_if_add() | | | | Cc: stable@vger.kernel.org Signed-off-by: NSumit Garg <sumit.garg@linaro.org> Link: https://lore.kernel.org/r/1586254255-28713-1-git-send-email-sumit.garg@linaro.org [Johannes: fix rtnl imbalances] Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
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