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[103.168.172.201]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6dd181c0fc5sm10672416d6.92.2024.12.19.14.27.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Dec 2024 14:27:40 -0800 (PST) Received: from phl-compute-12.internal (phl-compute-12.phl.internal [10.202.2.52]) by mailfauth.phl.internal (Postfix) with ESMTP id D540A1200069; Thu, 19 Dec 2024 17:27:39 -0500 (EST) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-12.internal (MEProxy); Thu, 19 Dec 2024 17:27:39 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefuddruddttddgudehlecutefuodetggdotefrod ftvfcurfhrohhfihhlvgemucfhrghsthforghilhdpggftfghnshhusghstghrihgsvgdp uffrtefokffrpgfnqfghnecuuegrihhlohhuthemuceftddtnecunecujfgurhepfffhvf evuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepuehoqhhunhcuhfgvnhhguceo sghoqhhunhdrfhgvnhhgsehgmhgrihhlrdgtohhmqeenucggtffrrghtthgvrhhnpeehud fgudffffetuedtvdehueevledvhfelleeivedtgeeuhfegueevieduffeivdenucevlhhu shhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpegsohhquhhnodhmvg hsmhhtphgruhhthhhpvghrshhonhgrlhhithihqdeiledvgeehtdeigedqudejjeekheeh hedvqdgsohhquhhnrdhfvghngheppehgmhgrihhlrdgtohhmsehfihigmhgvrdhnrghmvg dpnhgspghrtghpthhtohepuddvpdhmohguvgepshhmthhpohhuthdprhgtphhtthhopehr hihothhkkhhrleeksehgmhgrihhlrdgtohhmpdhrtghpthhtohepphgvthgvrhiisehinh hfrhgruggvrggurdhorhhgpdhrtghpthhtohepsghighgvrghshieslhhinhhuthhrohhn ihigrdguvgdprhgtphhtthhopegtlhhrkhiflhhlmhhssehkvghrnhgvlhdrohhrghdprh gtphhtthhopehlihhnuhigqdhkvghrnhgvlhesvhhgvghrrdhkvghrnhgvlhdrohhrghdp rhgtphhtthhopehlihhnuhigqdhrthdquggvvhgvlheslhhishhtshdrlhhinhhugidrug gvvhdprhgtphhtthhopehlohhnghhmrghnsehrvgguhhgrthdrtghomhdprhgtphhtthho pehmihhnghhosehrvgguhhgrthdrtghomhdprhgtphhtthhopehrohhsthgvughtsehgoh houghmihhsrdhorhhg X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 19 Dec 2024 17:27:39 -0500 (EST) Date: Thu, 19 Dec 2024 14:27:11 -0800 From: Boqun Feng To: Ryo Takakura Cc: peterz@infradead.org, bigeasy@linutronix.de, clrkwllms@kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, longman@redhat.com, mingo@redhat.com, rostedt@goodmis.org, tglx@linutronix.de, will@kernel.org Subject: Re: [PATCH] lockdep: Fix wait context check on softirq for PREEMPT_RT Message-ID: References: <20241209160943.254299-1-ryotkkr98@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241209160943.254299-1-ryotkkr98@gmail.com> On Tue, Dec 10, 2024 at 01:09:43AM +0900, Ryo Takakura wrote: > Hi! > > Sorry for being late on reply. I was trying to understand some > of the selftest reports that came across... > > On Mon, 2 Dec 2024 23:49:24 -0800, Boqun Feng wrote: > >Maybe the right way to fix this is adding a conceptual local_lock for > >BH disable like below. > > > >Regards, > >Boqun > > > >------------------------->8 > >diff --git a/include/linux/bottom_half.h b/include/linux/bottom_half.h > >index fc53e0ad56d9..d5b898588277 100644 > >--- a/include/linux/bottom_half.h > >+++ b/include/linux/bottom_half.h > >@@ -4,6 +4,7 @@ > > > > #include > > #include > >+#include > > > > #if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_TRACE_IRQFLAGS) > > extern void __local_bh_disable_ip(unsigned long ip, unsigned int cnt); > >@@ -15,9 +16,12 @@ static __always_inline void __local_bh_disable_ip(unsigned long ip, unsigned int > > } > > #endif > > > >+extern struct lockdep_map bh_lock_map; > >+ > > static inline void local_bh_disable(void) > > { > > __local_bh_disable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET); > >+ lock_map_acquire(&bh_lock_map); > > } > > > > extern void _local_bh_enable(void); > >@@ -25,6 +29,7 @@ extern void __local_bh_enable_ip(unsigned long ip, unsigned int cnt); > > > > static inline void local_bh_enable_ip(unsigned long ip) > > { > >+ lock_map_release(&bh_lock_map); > > __local_bh_enable_ip(ip, SOFTIRQ_DISABLE_OFFSET); > > } > > Maybe &bh_lock_map should be acquired at local_bh_enable()? > Right, local_bh_enable_ip() seems to be an unused function... > static inline void local_bh_enable(void) > { > + lock_map_release(&bh_lock_map); > __local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET); > } > > On !CONFIG_PREEMPT_RT, I noticed that softirq related selftests > (e.g. lock-inversion) fails with recursive locking error > > [ 0.741422] ============================================ > [ 0.741447] WARNING: possible recursive locking detected > [ 0.741471] 6.12.0-rc1-v8+ #25 Not tainted > [ 0.741495] -------------------------------------------- > [ 0.741519] swapper/0/0 is trying to acquire lock: > [ 0.741544] ffffffecd02e0160 (local_bh){+.+.}-{1:3}, at: irq_inversion_soft_spin_123+0x0/0x178 > [ 0.741621] > but task is already holding lock: > [ 0.741648] ffffffecd02e0160 (local_bh){+.+.}-{1:3}, at: irq_inversion_soft_spin_123+0x0/0x178 > [ 0.741721] > other info that might help us debug this: > [ 0.741750] Possible unsafe locking scenario: > > [ 0.741776] CPU0 > [ 0.741793] ---- > [ 0.741810] lock(local_bh); > [ 0.741840] lock(local_bh); > [ 0.741868] > *** DEADLOCK *** > > where it does SOFTIRQ_ENTER()/EXIT() and SOFTIRQ_DISABLE()/ENABLE() > as each enables BH with local_bh_enable(). > > But I was little confused that isn't recursively disabling BH allowed, > especially if PREEMPT_RT doesn't disable preemption? (I was also > wondering if disabling BH recursively is something that can happen > on !PREEMPT_RT if it disables preemption...) > If so, wouldn't report for such case be false? > I think you're right. Recursively BH disabling should be allowed, what I missed was that we should use lock_map_acquire_read() instead of lock_map_acquire() in local_bh_disable(). Because as you said, recursively BH disabling should be allowed therefore the virtual "lock" of BH disabling should be a read lock. The following is the rough idea: Regards, Boqun ----->8 diff --git a/include/linux/bottom_half.h b/include/linux/bottom_half.h index fc53e0ad56d9..7191a753e983 100644 --- a/include/linux/bottom_half.h +++ b/include/linux/bottom_half.h @@ -4,6 +4,7 @@ #include #include +#include #if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_TRACE_IRQFLAGS) extern void __local_bh_disable_ip(unsigned long ip, unsigned int cnt); @@ -15,9 +16,12 @@ static __always_inline void __local_bh_disable_ip(unsigned long ip, unsigned int } #endif +extern struct lockdep_map bh_lock_map; + static inline void local_bh_disable(void) { __local_bh_disable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET); + lock_map_acquire_read(&bh_lock_map); } extern void _local_bh_enable(void); @@ -25,11 +29,13 @@ extern void __local_bh_enable_ip(unsigned long ip, unsigned int cnt); static inline void local_bh_enable_ip(unsigned long ip) { + lock_map_release(&bh_lock_map); __local_bh_enable_ip(ip, SOFTIRQ_DISABLE_OFFSET); } static inline void local_bh_enable(void) { + lock_map_release(&bh_lock_map); __local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET); } diff --git a/kernel/softirq.c b/kernel/softirq.c index 8b41bd13cc3d..17d9bf6e0caf 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -1066,3 +1066,13 @@ unsigned int __weak arch_dynirq_lower_bound(unsigned int from) { return from; } + +static struct lock_class_key bh_lock_key; +struct lockdep_map bh_lock_map = { + .name = "local_bh", + .key = &bh_lock_key, + .wait_type_outer = LD_WAIT_FREE, + .wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT makes BH preemptible. */ + .lock_type = LD_LOCK_PERCPU, +}; +EXPORT_SYMBOL_GPL(bh_lock_map);