Hi,

On Mon, Nov 29, 2021 at 4:47 PM Brian Norris [off-list ref] wrote:

Quoting Jia-Ju Bai [off-list ref]:

  mwifiex_dequeue_tx_packet()
     spin_lock_bh(&priv->wmm.ra_list_spinlock); --> Line 1432 (Lock A)
     mwifiex_send_addba()
       spin_lock_bh(&priv->sta_list_spinlock); --> Line 608 (Lock B)

  mwifiex_process_sta_tx_pause()
     spin_lock_bh(&priv->sta_list_spinlock); --> Line 398 (Lock B)
     mwifiex_update_ralist_tx_pause()
       spin_lock_bh(&priv->wmm.ra_list_spinlock); --> Line 941 (Lock A)

Similar report for mwifiex_process_uap_tx_pause().

While the locking expectations in this driver are a bit unclear, the
Fixed commit only intended to protect the sta_ptr, so we can drop the
lock as soon as we're done with it.

IIUC, this deadlock cannot actually happen, because command event
processing (which calls mwifiex_process_sta_tx_pause()) is
sequentialized with TX packet processing (e.g.,
mwifiex_dequeue_tx_packet()) via the main loop (mwifiex_main_process()).
But it's good not to leave this potential issue lurking.

Fixes: ("f0f7c2275fb9 mwifiex: minor cleanups w/ sta_list_spinlock in cfg80211.c")
Cc: Douglas Anderson <dianders@chromium.org>
Reported-by: TOTE Robot <redacted>
Link: https://lore.kernel.org/linux-wireless/0e495b14-efbb-e0da-37bd-af6bd677ee2c@gmail.com/ (local)
Signed-off-by: Brian Norris <briannorris@chromium.org>
---

On Tue, Nov 23, 2021 at 11:31:34AM +0800, Jia-Ju Bai wrote:

quoted

I am not quite sure whether these possible deadlocks are real and how to fix
them if they are real.
Any feedback would be appreciated, thanks :)

I think these are at least theoretically real, and so we should take
something like the $subject patch probably. But I don't believe we can
actually hit this due to the main-loop structure of this driver.

Anyway, see the surrounding patch.

Thanks,
Brian


 drivers/net/wireless/marvell/mwifiex/sta_event.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Though I'm by no means an expert on this code and I wrote the patch in
question a long time ago, this seems reasonable to me. Thanks for
fixing.

Reviewed-by: Douglas Anderson <dianders@chromium.org>