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If channel switch is pending and we remove interface we can
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crash like showed below due to passing NULL vif to mac80211:
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BUG: unable to handle kernel paging request at fffffffffffff8cc
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IP: [<ffffffff8130924d>] strnlen+0xd/0x40
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Call Trace:
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 [<ffffffff8130ad2e>] string.isra.3+0x3e/0xd0
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 [<ffffffff8130bf99>] vsnprintf+0x219/0x640
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 [<ffffffff8130c481>] vscnprintf+0x11/0x30
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 [<ffffffff81061585>] vprintk_emit+0x115/0x4f0
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 [<ffffffff81657bd5>] printk+0x61/0x63
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 [<ffffffffa048987f>] ieee80211_chswitch_done+0xaf/0xd0 [mac80211]
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 [<ffffffffa04e7b34>] iwl_chswitch_done+0x34/0x40 [iwldvm]
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 [<ffffffffa04f83c3>] iwlagn_commit_rxon+0x2a3/0xdc0 [iwldvm]
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 [<ffffffffa04ebc50>] ? iwlagn_set_rxon_chain+0x180/0x2c0 [iwldvm]
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 [<ffffffffa04e5e76>] iwl_set_mode+0x36/0x40 [iwldvm]
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 [<ffffffffa04e5f0d>] iwlagn_mac_remove_interface+0x8d/0x1b0 [iwldvm]
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 [<ffffffffa0459b3d>] ieee80211_do_stop+0x29d/0x7f0 [mac80211]
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This is because we nulify ctx->vif in iwlagn_mac_remove_interface()
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before calling some other functions that teardown interface. To fix
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just check ctx->vif on iwl_chswitch_done(). We should not call
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ieee80211_chswitch_done() as channel switch works were already canceled
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by mac80211 in ieee80211_do_stop() -> ieee80211_mgd_stop().
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Resolve:
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https://bugzilla.redhat.com/show_bug.cgi?id=979581
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Cc: stable@vger.kernel.org
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Reported-by: Lukasz Jagiello <jagiello.lukasz@gmail.com>
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Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
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---
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 drivers/net/wireless/iwlwifi/dvm/mac80211.c | 5 ++++-
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 1 file changed, 4 insertions(+), 1 deletion(-)
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diff --git a/drivers/net/wireless/iwlwifi/dvm/mac80211.c b/drivers/net/wireless/iwlwifi/dvm/mac80211.c
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index 323e4a3..9a817df 100644
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--- a/drivers/net/wireless/iwlwifi/dvm/mac80211.c
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+++ b/drivers/net/wireless/iwlwifi/dvm/mac80211.c
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@@ -1046,7 +1046,10 @@ void iwl_chswitch_done(struct iwl_priv *priv, bool is_success)
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 	if (test_bit(STATUS_EXIT_PENDING, &priv->status))
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 		return;
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-	if (test_and_clear_bit(STATUS_CHANNEL_SWITCH_PENDING, &priv->status))
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+	if (!test_and_clear_bit(STATUS_CHANNEL_SWITCH_PENDING, &priv->status))
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+		return;
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+
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+	if (ctx->vif)
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 		ieee80211_chswitch_done(ctx->vif, is_success);
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 }
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-- 
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1.7.11.7
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--
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