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[219.110.108.104]) by smtp.gmail.com with ESMTPSA id t14sm2071701pfg.168.2021.05.13.06.39.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 May 2021 06:39:53 -0700 (PDT) Received: from localhost ([127.0.0.1] helo=jrobl) by jrobl id 1lhBZ9-00080i-LW ; Thu, 13 May 2021 22:39:51 +0900 From: "J. R. Okajima" To: peterz@infradead.org, penguin-kernel@I-love.SAKURA.ne.jp Cc: linux-kernel@vger.kernel.org Subject: LOCKDEP customizable numbers upper limit MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <30794.1620913191.1@jrobl> Date: Thu, 13 May 2021 22:39:51 +0900 Message-ID: <30795.1620913191@jrobl> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, According to the commit in v5.13-rc1, 5dc33592e9553 2021-04-05 lockdep: Allow tuning tracing capacity constants. several lockdep numbers have their own range as 10--30. But if we set all 30s, we got a compilation error. kernel/locking/lockdep.c:3536:2: note: in expansion of macro 'BUILD_BUG_ON' BUILD_BUG_ON((1UL << 24) <= ARRAY_SIZE(chain_hlocks)); kernel/locking/lockdep.c ---------------------------------------- static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS]; ::: BUILD_BUG_ON((1UL << 24) <= ARRAY_SIZE(chain_hlocks)); ::: ---------------------------------------- MAX_LOCKDEP_CHAIN_HLOCKS is defined in kernel/locking/lockdep_internal.h as this. #define MAX_LOCKDEP_CHAINS_BITS CONFIG_LOCKDEP_CHAINS_BITS #define MAX_LOCKDEP_CHAINS (1UL << MAX_LOCKDEP_CHAINS_BITS) #define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5) I don't know what this 'multiply by 5' means and why ARRAY_SIZE(chain_hlocks) is limited to (1UL << 24), but setting 30 to CONFIG_LOCKDEP_CHAINS_BITS obviously causes BUILD_BUG. '*5' is more than 2 bits shift, so CONFIG_LOCKDEP_CHAINS_BITS has to be less than (24-2), limited to the range 10--21. Hmm, I tried. CONFIG_LOCKDEP_BITS=30 CONFIG_LOCKDEP_CHAINS_BITS=21 CONFIG_LOCKDEP_STACK_TRACE_BITS=30 CONFIG_LOCKDEP_STACK_TRACE_HASH_BITS=30 CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS=30 Arg, LD failed. ld: kernel/locking/lockdep.o: in function `lockdep_hlock_class': lockdep.c:(.text+0x84f): relocation truncated to fit: R_X86_64_PC32 against `.bss' I am afraid these LOCKDEP configurations need some sort of balancing. J. R. Okajima