netdev - Re: [PATCH v2] cfg80211: avoid holding the RTNL when calling the driver

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Date:   Mon, 25 Jan 2021 13:34:14 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-wireless@...r.kernel.org
Cc:     netdev@...r.kernel.org, Oliver Neukum <oneukum@...e.com>
Subject: Re: [PATCH v2] cfg80211: avoid holding the RTNL when calling the
 driver

Hi Marek,

> I've checked today's linux-next with the updated commit 27bc93583e35 
> ("cfg80211: avoid holding the RTNL when calling the driver") and there 
> is still an issue there, but at least it doesn't cause a deadlock:
> 
> cfg80211: Loading compiled-in X.509 certificates for regulatory database
> Bluetooth: vendor=0x2df, device=0x912a, class=255, fn=2
> cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7'
> Bluetooth: FW download over, size 533976 bytes
> btmrvl_sdio mmc3:0001:2: sdio device tree data not available
> mwifiex_sdio mmc3:0001:1: WLAN FW already running! Skip FW dnld
> mwifiex_sdio mmc3:0001:1: WLAN FW is active
> mwifiex_sdio mmc3:0001:1: CMD_RESP: cmd 0x242 error, result=0x2
> mwifiex_sdio mmc3:0001:1: mwifiex_process_cmdresp: cmd 0x242 failed 
> during       initialization
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 5 at net/wireless/core.c:1336 
> cfg80211_register_netdevice+0xa4/0x198 [cfg80211]

Yeah, umm, brown paper bag style bug.

I meant to _move_ that line down, but somehow managed to _copy_ it down.
Need to just remove it since rdev is not even initialized at that point.

I've updated my tree to include this:

diff --git a/net/wireless/core.c b/net/wireless/core.c
index 5e8b523dc645..200cd9f5fd5f 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -1333,7 +1333,6 @@ int cfg80211_register_netdevice(struct net_device *dev)
        int ret;
 
        ASSERT_RTNL();
-       lockdep_assert_held(&rdev->wiphy.mtx);
 
        if (WARN_ON(!wdev))
                return -EINVAL;

johannes