linux-kernel - [RFC PATCH 8/8] ARM: rely on core code to keep thread

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Date:   Tue, 14 Sep 2021 14:10:36 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org
Subject: [RFC PATCH 8/8] ARM: rely on core code to keep thread_info::cpu updated

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@...nel.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