linux-kernel - [PATCH 3/9] arm64: Mark __switch_to() as _

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Message-Id: <20211117140737.44420-4-mark.rutland@arm.com>
Date:   Wed, 17 Nov 2021 14:07:31 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     aou@...s.berkeley.edu, borntraeger@...ibm.com, bp@...en8.de,
        broonie@...nel.org, catalin.marinas@....com,
        dave.hansen@...ux.intel.com, gor@...ux.ibm.com, hca@...ux.ibm.com,
        linux-kernel@...r.kernel.org, madvenka@...ux.microsoft.com,
        mark.rutland@....com, mhiramat@...nel.org, mingo@...hat.com,
        mpe@...erman.id.au, palmer@...belt.com, paul.walmsley@...ive.com,
        peterz@...radead.org, rostedt@...dmis.org, tglx@...utronix.de,
        will@...nel.org
Subject: [PATCH 3/9] arm64: Mark __switch_to() as __sched

Unlike most architectures (and only in keeping with powerpc), arm64 has
a non __sched() function on the path to our cpu_switch_to() assembly
function.

It is expected that for a blocked task, in_sched_functions() can be used
to skip all functions between the raw context switch assembly and the
scheduler functions that call into __switch_to(). This is the behaviour
expected by stack_trace_consume_entry_nosched(), and the behaviour we'd
like to have such that we an simplify arm64's __get_wchan()
implementation to use arch_stack_walk().

This patch mark's arm64's __switch_to as __sched. This *will not* change
the behaviour of arm64's current __get_wchan() implementation, which
always performs an initial unwind step which skips __switch_to(). This
*will* change the behaviour of stack_trace_consume_entry_nosched() and
stack_trace_save_tsk() to match their expected behaviour on blocked
tasks, skipping all scheduler-internal functions including
__switch_to().

Other than the above, there should be no functional change as a result
of this patch.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Will Deacon <will@...nel.org>
---
 arch/arm64/kernel/process.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index aacf2f5559a8..980cad7292af 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -490,7 +490,8 @@ void update_sctlr_el1(u64 sctlr)
 /*
  * Thread switching.
  */
-__notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
+__notrace_funcgraph __sched
+struct task_struct *__switch_to(struct task_struct *prev,
 				struct task_struct *next)
 {
 	struct task_struct *last;
-- 
2.11.0