linux-kernel - [PATCH] hrtimer: Fix the incorrect initialization of timer->is

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Message-Id: <20250321015128.1393009-1-cuiguoqi@kylinos.cn>
Date: Fri, 21 Mar 2025 09:51:28 +0800
From: cuiguoqi <cuiguoqi@...inos.cn>
To: anna-maria@...utronix.de
Cc: frederic@...nel.org,
	tglx@...utronix.de,
	linux-kernel@...r.kernel.org,
	bigeasy@...utronix.de,
	clrkwllms@...nel.org,
	rostedt@...dmis.org,
	linux-rt-devel@...ts.linux.dev,
	cuiguoqi <cuiguoqi@...inos.cn>
Subject: [PATCH] hrtimer: Fix the incorrect initialization of timer->is_hard

When PREEMPT_RT is disabled,there is a possibility that
timer->is_hard will be incorrectly initialized.
When creating a high-resolution timer and setting the mode to
HRTIMER_MODE_ABS,the timer->is_hard will be incorrectly initialized.

Pseudocode logic:
1. mode
   >> HRTIMER_MODE_ABS	= 0x00

2. bool softtimer = !!(mode & HRTIMER_MODE_SOFT);	//!PREEMPT_RT
   base = softtimer ? HRTIMER_MAX_CLOCK_BASES / 2 : 0;	//!PREEMPT_RT
   > softtimer = false；				//!PREEMPT_RT
   > base = 0;						//hard mode

3. timer->is_soft = softtimer;
   > timer->is_soft = flase;

4. timer->is_hard = !!(mode & HRTIMER_MODE_HARD);	!PREEMPT_RT
   >  timer->is_hard = flase;				//error
   >  Based on point 2, by default, the hard mode is selected.

Of course, if PREEMPT_RT is enabled, timer->is_hard is correctly set.
   bool softtimer = !!(mode & HRTIMER_MODE_SOFT);
   if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(mode & HRTIMER_MODE_HARD))
	softtimer = true;
   timer->is_soft = softtimer;				//true
   timer->is_hard = !!(mode & HRTIMER_MODE_HARD);	//flase

Signed-off-by: cuiguoqi <cuiguoqi@...inos.cn>
---
 kernel/time/hrtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 80fe3749d2db..9d8defb1e9b1 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1571,7 +1571,7 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
 	base = softtimer ? HRTIMER_MAX_CLOCK_BASES / 2 : 0;
 	base += hrtimer_clockid_to_base(clock_id);
 	timer->is_soft = softtimer;
-	timer->is_hard = !!(mode & HRTIMER_MODE_HARD);
+	timer->is_hard = !softtimer;
 	timer->base = &cpu_base->clock_base[base];
 	timerqueue_init(&timer->node);
 }
-- 
2.25.1