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[2001:1c00:c1e:bf00:37a3:353b:be90:1238]) by smtp.gmail.com with ESMTPSA id m26sm4865344ejr.54.2021.01.18.13.09.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 Jan 2021 13:09:03 -0800 (PST) Subject: Re: [PATCH] cfg80211: Fix "suspicious RCU usage in wiphy_apply_custom_regulatory" warning/backtrace To: "Peer, Ilan" , Johannes Berg , "David S . Miller" , Jakub Kicinski , "Rojewski, Cezary" , Pierre-Louis Bossart , Liam Girdwood , Jie Yang , Mark Brown Cc: "linux-wireless@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "alsa-devel@alsa-project.org" References: <20210104170713.66956-1-hdegoede@redhat.com> From: Hans de Goede Message-ID: <391ac436-9981-0f12-6e00-7a1bbe4d5c20@redhat.com> Date: Mon, 18 Jan 2021 22:09:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi, On 1/5/21 10:24 AM, Peer, Ilan wrote: > Hi, > >> -----Original Message----- >> From: Hans de Goede >> Sent: Monday, January 04, 2021 19:07 >> To: Johannes Berg ; David S . Miller >> ; Jakub Kicinski ; Rojewski, >> Cezary ; Pierre-Louis Bossart > louis.bossart@linux.intel.com>; Liam Girdwood >> ; Jie Yang ; >> Mark Brown >> Cc: Hans de Goede ; linux- >> wireless@vger.kernel.org; netdev@vger.kernel.org; linux- >> kernel@vger.kernel.org; alsa-devel@alsa-project.org; Peer, Ilan >> >> Subject: [PATCH] cfg80211: Fix "suspicious RCU usage in >> wiphy_apply_custom_regulatory" warning/backtrace >> >> Commit beee24695157 ("cfg80211: Save the regulatory domain when setting >> custom regulatory") adds a get_wiphy_regdom call to >> wiphy_apply_custom_regulatory. But as the comment above >> wiphy_apply_custom_regulatory says: >> "/* Used by drivers prior to wiphy registration */" >> this function is used by driver's probe function before the wiphy is registered >> and at this point wiphy->regd will typically by NULL and calling >> rcu_dereference_rtnl on a NULL pointer causes the following >> warning/backtrace: >> >> ============================= >> WARNING: suspicious RCU usage >> 5.11.0-rc1+ #19 Tainted: G W >> ----------------------------- >> net/wireless/reg.c:144 suspicious rcu_dereference_check() usage! >> >> other info that might help us debug this: >> >> rcu_scheduler_active = 2, debug_locks = 1 >> 2 locks held by kworker/2:0/22: >> #0: ffff9a4bc104df38 ((wq_completion)events){+.+.}-{0:0}, at: >> process_one_work+0x1ee/0x570 >> #1: ffffb6e94010be78 ((work_completion)(&fw_work->work)){+.+.}-{0:0}, >> at: process_one_work+0x1ee/0x570 >> >> stack backtrace: >> CPU: 2 PID: 22 Comm: kworker/2:0 Tainted: G W 5.11.0-rc1+ #19 >> Hardware name: LENOVO 60073/INVALID, BIOS 01WT17WW 08/01/2014 >> Workqueue: events request_firmware_work_func Call Trace: >> dump_stack+0x8b/0xb0 >> get_wiphy_regdom+0x57/0x60 [cfg80211] >> wiphy_apply_custom_regulatory+0xa0/0xf0 [cfg80211] >> brcmf_cfg80211_attach+0xb02/0x1360 [brcmfmac] >> brcmf_attach+0x189/0x460 [brcmfmac] >> brcmf_sdio_firmware_callback+0x78a/0x8f0 [brcmfmac] >> brcmf_fw_request_done+0x67/0xf0 [brcmfmac] >> request_firmware_work_func+0x3d/0x70 >> process_one_work+0x26e/0x570 >> worker_thread+0x55/0x3c0 >> ? process_one_work+0x570/0x570 >> kthread+0x137/0x150 >> ? __kthread_bind_mask+0x60/0x60 >> ret_from_fork+0x22/0x30 >> >> Add a check for wiphy->regd being NULL before calling get_wiphy_regdom >> (as is already done in other places) to fix this. >> >> wiphy->regd will likely always be NULL when >> wiphy->wiphy_apply_custom_regulatory >> gets called, so arguably the tmp = get_wiphy_regdom() and >> rcu_free_regdom(tmp) calls should simply be dropped, this patch keeps the >> 2 calls, to allow drivers to call wiphy_apply_custom_regulatory more then >> once if necessary. >> >> Cc: Ilan Peer >> Fixes: beee24695157 ("cfg80211: Save the regulatory domain when setting >> custom regulator") >> Signed-off-by: Hans de Goede >> --- >> net/wireless/reg.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/net/wireless/reg.c b/net/wireless/reg.c index >> bb72447ad960..9254b9cbaa21 100644 >> --- a/net/wireless/reg.c >> +++ b/net/wireless/reg.c >> @@ -2547,7 +2547,7 @@ static void handle_band_custom(struct wiphy >> *wiphy, void wiphy_apply_custom_regulatory(struct wiphy *wiphy, >> const struct ieee80211_regdomain *regd) { >> - const struct ieee80211_regdomain *new_regd, *tmp; >> + const struct ieee80211_regdomain *new_regd, *tmp = NULL; >> enum nl80211_band band; >> unsigned int bands_set = 0; >> >> @@ -2571,7 +2571,8 @@ void wiphy_apply_custom_regulatory(struct wiphy >> *wiphy, >> if (IS_ERR(new_regd)) >> return; >> >> - tmp = get_wiphy_regdom(wiphy); >> + if (wiphy->regd) >> + tmp = get_wiphy_regdom(wiphy); >> rcu_assign_pointer(wiphy->regd, new_regd); >> rcu_free_regdom(tmp); > > This only fixes the first case where the pointer in NULL and does not handle the wrong RCU usage in other cases. > > I'll prepare a fix for this. Any luck with this? This is a regression in 5.11, so this really should be fixed in a future 5.11-rc and the clock is running out. Regards, Hans