Commit 616ab35d authored by Koichiro Den's avatar Koichiro Den Committed by Zeng Heng
Browse files

hrtimers: Handle CPU state correctly on hotplug 

stable inclusion
from stable-v5.10.234
commit 14984139f1f2768883332965db566ef26db609e7
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IBLWTN
CVE: CVE-2024-57951

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14984139f1f2768883332965db566ef26db609e7



--------------------------------

commit 2f8dea1692eef2b7ba6a256246ed82c365fdc686 upstream.

Consider a scenario where a CPU transitions from CPUHP_ONLINE to halfway
through a CPU hotunplug down to CPUHP_HRTIMERS_PREPARE, and then back to
CPUHP_ONLINE:

Since hrtimers_prepare_cpu() does not run, cpu_base.hres_active remains set
to 1 throughout. However, during a CPU unplug operation, the tick and the
clockevents are shut down at CPUHP_AP_TICK_DYING. On return to the online
state, for instance CFS incorrectly assumes that the hrtick is already
active, and the chance of the clockevent device to transition to oneshot
mode is also lost forever for the CPU, unless it goes back to a lower state
than CPUHP_HRTIMERS_PREPARE once.

This round-trip reveals another issue; cpu_base.online is not set to 1
after the transition, which appears as a WARN_ON_ONCE in enqueue_hrtimer().

Aside of that, the bulk of the per CPU state is not reset either, which
means there are dangling pointers in the worst case.

Address this by adding a corresponding startup() callback, which resets the
stale per CPU state and sets the online flag.

[ tglx: Make the new callback unconditionally available, remove the online
  	modification in the prepare() callback and clear the remaining
  	state in the starting callback instead of the prepare callback ]

Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")
Signed-off-by: default avatarKoichiro Den <koichiro.den@canonical.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20241220134421.3809834-1-koichiro.den@canonical.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Conflicts:
	kernel/cpu.c
[commit 1426c91277cc ("cpu/hotplug: Fix kabi breakage in enum cpuhp_state")
 removed CPUHP_AP_HRTIMERS_DYING to fix kabi changes]
Signed-off-by: default avatarZeng Heng <zengheng4@huawei.com>
parent c81b4f78

include/linux/hrtimer.h

+1 −0
Original line number Diff line number Diff line
@@ -545,6 +545,7 @@ extern void __init hrtimers_init(void); 
extern void sysrq_timer_list_show(void);



int hrtimers_prepare_cpu(unsigned int cpu);

int hrtimers_cpu_starting(unsigned int cpu);

#ifdef CONFIG_HOTPLUG_CPU

int hrtimers_cpu_dying(unsigned int cpu);

#else

kernel/cpu.c

+8 −1
Original line number Diff line number Diff line
@@ -1713,9 +1713,16 @@ static struct cpuhp_step cpuhp_hp_states[] = { 
	 * Please ensure that there are no other steps with teardown handler

	 * between smpcfd:dying and cpu:teardown.

	 */

	/*

	 * In the past, the implementation of CPUHP_AP_HRTIMERS_DYING is deleted because

	 * the Kabi is fixed. The teardown operation and teardown of CPUHP_AP_SMPCFD_DYING

	 * are combined into smpcfd_and_hrtimer_dying_cpu. The startup operation of

	 * CPUHP_AP_SMPCFD_DYING is empty. Therefore, the startup operation of

	 * hrtimers_cpu_starting is set to the startup operation of CPUHP_AP_SMPCFD_DYING.

	 */

	[CPUHP_AP_SMPCFD_DYING] = {

		.name			= "smpcfd:dying",

		.startup.single		= NULL,

		.startup.single		= hrtimers_cpu_starting,

		.teardown.single	= smpcfd_and_hrtimer_dying_cpu,

	},

kernel/time/hrtimer.c

+10 −1
Original line number Diff line number Diff line
@@ -2136,6 +2136,15 @@ int hrtimers_prepare_cpu(unsigned int cpu) 
	}



	cpu_base->cpu = cpu;

	hrtimer_cpu_base_init_expiry_lock(cpu_base);

	return 0;

}



int hrtimers_cpu_starting(unsigned int cpu)

{

	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);



	/* Clear out any left over state from a CPU down operation */

	cpu_base->active_bases = 0;

	cpu_base->hres_active = 0;

	cpu_base->hang_detected = 0;
@@ -2144,7 +2153,6 @@ int hrtimers_prepare_cpu(unsigned int cpu) 
	cpu_base->expires_next = KTIME_MAX;

	cpu_base->softirq_expires_next = KTIME_MAX;

	cpu_base->online = 1;

	hrtimer_cpu_base_init_expiry_lock(cpu_base);

	return 0;

}
@@ -2222,6 +2230,7 @@ int hrtimers_cpu_dying(unsigned int dying_cpu) 
void __init hrtimers_init(void)

{

	hrtimers_prepare_cpu(smp_processor_id());

	hrtimers_cpu_starting(smp_processor_id());

	open_softirq(HRTIMER_SOFTIRQ, hrtimer_run_softirq);

}