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[24.9.64.241]) by smtp.gmail.com with ESMTPSA id r13sm435237oot.41.2021.02.10.07.57.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Feb 2021 07:57:05 -0800 (PST) Subject: Re: [PATCH 4/5] ath10k: detect conf_mutex held ath10k_drain_tx() calls To: Kalle Valo Cc: davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, ath10k@lists.infradead.org, Shuah Khan References: <87lfbwtjls.fsf@codeaurora.org> From: Shuah Khan Message-ID: Date: Wed, 10 Feb 2021 08:57:04 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <87lfbwtjls.fsf@codeaurora.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On 2/10/21 1:25 AM, Kalle Valo wrote: > Shuah Khan writes: > >> ath10k_drain_tx() must not be called with conf_mutex held as workers can >> use that also. Add check to detect conf_mutex held calls. >> >> Signed-off-by: Shuah Khan > > The commit log does not answer to "Why?". How did you find this? What > actual problem are you trying to solve? > I came across the comment block above the ath10k_drain_tx() as I was reviewing at conf_mutex holds while I was debugging the conf_mutex lock assert in ath10k_debug_fw_stats_request(). My reasoning is that having this will help detect incorrect usages of ath10k_drain_tx() while holding conf_mutex which could lead to locking problems when async worker routines try to call this routine. >> --- >> drivers/net/wireless/ath/ath10k/mac.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c >> index 53f92945006f..3545ce7dce0a 100644 >> --- a/drivers/net/wireless/ath/ath10k/mac.c >> +++ b/drivers/net/wireless/ath/ath10k/mac.c >> @@ -4566,6 +4566,7 @@ static void ath10k_mac_op_wake_tx_queue(struct ieee80211_hw *hw, >> /* Must not be called with conf_mutex held as workers can use that also. */ >> void ath10k_drain_tx(struct ath10k *ar) >> { >> + WARN_ON(lockdep_is_held(&ar->conf_mutex)); > > Empty line after WARN_ON(). > Will do. > Shouldn't this check debug_locks similarly lockdep_assert_held() does? > > #define lockdep_assert_held(l) do { \ > WARN_ON(debug_locks && !lockdep_is_held(l)); \ > } while (0) > > And I suspect you need #ifdef CONFIG_LOCKDEP which should fix the kbuild > bot error. > Yes. > But honestly I would prefer to have lockdep_assert_not_held() in > include/linux/lockdep.h, much cleaner that way. Also > i915_gem_object_lookup_rcu() could then use the same macro. > Right. This is the right way to go. That was first instinct and decided to have the discussion evolve in that direction. Now that it has, I will combine this change with include/linux/lockdep.h and add lockdep_assert_not_held() I think we might have other places in the kernel that could use lockdep_assert_not_held() in addition to i915_gem_object_lookup_rcu() thanks, -- Shuah