linux-kernel - [PATCH v2 3/5] ARM: stacktrace: Allow stack trace saving for non-current tasks

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Message-ID: <20220713110020.85511-4-lihuafei1@huawei.com>
Date:   Wed, 13 Jul 2022 19:00:18 +0800
From:   Li Huafei <lihuafei1@...wei.com>
To:     <linux@...linux.org.uk>, <rmk+kernel@...linux.org.uk>,
        <ardb@...nel.org>, <will@...nel.org>, <broonie@...nel.org>
CC:     <mark.rutland@....com>, <peterz@...radead.org>, <mingo@...hat.com>,
        <acme@...nel.org>, <alexander.shishkin@...ux.intel.com>,
        <jolsa@...nel.org>, <namhyung@...nel.org>, <arnd@...db.de>,
        <linus.walleij@...aro.org>, <rostedt@...dmis.org>,
        <nick.hawkins@....com>, <john@...ozen.org>, <mhiramat@...nel.org>,
        <ast@...nel.org>, <linyujun809@...wei.com>,
        <ndesaulniers@...gle.com>, <lihuafei1@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>
Subject: [PATCH v2 3/5] ARM: stacktrace: Allow stack trace saving for non-current tasks

The current ARM implementation of save_stack_trace_tsk() does not allow
saving stack trace for non-current tasks, which may limit the scenarios
in which stack_trace_save_tsk() can be used. Like other architectures,
or like ARM's unwind_backtrace(), we can leave it up to the caller to
ensure that the task that needs to be unwound is not running.

Signed-off-by: Li Huafei <lihuafei1@...wei.com>
---
 arch/arm/kernel/stacktrace.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
index 3acf51ee46bb..836420c00938 100644
--- a/arch/arm/kernel/stacktrace.c
+++ b/arch/arm/kernel/stacktrace.c
@@ -171,19 +171,11 @@ static noinline void __save_stack_trace(struct task_struct *tsk,
 	data.no_sched_functions = nosched;
 
 	if (tsk != current) {
-#ifdef CONFIG_SMP
-		/*
-		 * What guarantees do we have here that 'tsk' is not
-		 * running on another CPU?  For now, ignore it as we
-		 * can't guarantee we won't explode.
-		 */
-		return;
-#else
+		/* task blocked in __switch_to */
 		frame.fp = thread_saved_fp(tsk);
 		frame.sp = thread_saved_sp(tsk);
 		frame.lr = 0;		/* recovered from the stack */
 		frame.pc = thread_saved_pc(tsk);
-#endif
 	} else {
 		/* We don't want this function nor the caller */
 		data.skip += 2;
-- 
2.17.1