[RFC PATCH 8/8] ARM: rely on core code to keep thread_info::cpu updated

From: Ard Biesheuvel <ardb@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Keith Packard <keithpac@amazon.com>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Paul Mackerras <paulus@samba.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Kees Cook <keescook@chromium.org>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-arm-kernel@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org
Subject: [RFC PATCH 8/8] ARM: rely on core code to keep thread_info::cpu updated
Date: Tue, 14 Sep 2021 14:10:36 +0200	[thread overview]
Message-ID: <20210914121036.3975026-9-ardb@kernel.org> (raw)
In-Reply-To: <20210914121036.3975026-1-ardb@kernel.org>

Now that the core code switched back to using thread_info::cpu to keep
a task's CPU number, we no longer need to keep it in sync explicitly. So
just drop the code that does this.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
This patch applies onto [0], which we hope to get merged for v5.16

[0] https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=arm32-ti-in-task-v5

 arch/arm/include/asm/switch_to.h | 14 --------------
 arch/arm/kernel/smp.c            |  3 ---
 2 files changed, 17 deletions(-)

diff --git a/arch/arm/include/asm/switch_to.h b/arch/arm/include/asm/switch_to.h
index db2be1f6550d..61e4a3c4ca6e 100644
--- a/arch/arm/include/asm/switch_to.h
+++ b/arch/arm/include/asm/switch_to.h
@@ -23,23 +23,9 @@
  */
 extern struct task_struct *__switch_to(struct task_struct *, struct thread_info *, struct thread_info *);
 
-static inline void set_ti_cpu(struct task_struct *p)
-{
-#ifdef CONFIG_THREAD_INFO_IN_TASK
-	/*
-	 * The core code no longer maintains the thread_info::cpu field once
-	 * CONFIG_THREAD_INFO_IN_TASK is in effect, but we rely on it for
-	 * raw_smp_processor_id(), which cannot access struct task_struct*
-	 * directly for reasons of circular #inclusion hell.
-	 */
-	task_thread_info(p)->cpu = p->cpu;
-#endif
-}
-
 #define switch_to(prev,next,last)					\
 do {									\
 	__complete_pending_tlbi();					\
-	set_ti_cpu(next);						\
 	if (IS_ENABLED(CONFIG_CURRENT_POINTER_IN_TPIDRURO))		\
 		__this_cpu_write(__entry_task, next);			\
 	last = __switch_to(prev,task_thread_info(prev), task_thread_info(next));	\
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index cde5b6d8bac5..97ee6b1567e9 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -154,9 +154,6 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	secondary_data.swapper_pg_dir = get_arch_pgd(swapper_pg_dir);
 #endif
 	secondary_data.task = idle;
-	if (IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK))
-		task_thread_info(idle)->cpu = cpu;
-
 	sync_cache_w(&secondary_data);
 
 	/*
-- 
2.30.2


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