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    Subject[PATCH AUTOSEL 5.12 136/160] mac80211: Properly WARN on HW scan before restart
    Date
    From: Ilan Peer <ilan.peer@intel.com>

    [ Upstream commit 45daaa1318410794de956fb8e9d06aed2dbb23d0 ]

    The following race was possible:

    1. The device driver requests HW restart.
    2. A scan is requested from user space and is propagated
    to the driver. During this flow HW_SCANNING flag is set.
    3. The thread that handles the HW restart is scheduled,
    and before starting the actual reconfiguration it
    checks that HW_SCANNING is not set. The flow does so
    without acquiring any lock, and thus the WARN fires.

    Fix this by checking that HW_SCANNING is on only after RTNL is
    acquired, i.e., user space scan request handling is no longer
    in transit.

    Signed-off-by: Ilan Peer <ilan.peer@intel.com>
    Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
    Link: https://lore.kernel.org/r/iwlwifi.20210618133832.8238ab3e19ab.I2693c581c70251472b4f9089e37e06fb2c18268f@changeid
    Signed-off-by: Johannes Berg <johannes.berg@intel.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/mac80211/main.c | 7 +++----
    1 file changed, 3 insertions(+), 4 deletions(-)

    diff --git a/net/mac80211/main.c b/net/mac80211/main.c
    index 9dd741b68f26..937a024a13e2 100644
    --- a/net/mac80211/main.c
    +++ b/net/mac80211/main.c
    @@ -257,14 +257,13 @@ static void ieee80211_restart_work(struct work_struct *work)
    /* wait for scan work complete */
    flush_workqueue(local->workqueue);
    flush_work(&local->sched_scan_stopped_work);
    + flush_work(&local->radar_detected_work);
    +
    + rtnl_lock();

    WARN(test_bit(SCAN_HW_SCANNING, &local->scanning),
    "%s called with hardware scan in progress\n", __func__);

    - flush_work(&local->radar_detected_work);
    - /* we might do interface manipulations, so need both */
    - rtnl_lock();
    - wiphy_lock(local->hw.wiphy);
    list_for_each_entry(sdata, &local->interfaces, list) {
    /*
    * XXX: there may be more work for other vif types and even
    --
    2.30.2
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