Re: [syzbot] [kernel?] WARNING in hrtimer_forward (2)

Thomas Gleixner
2024-04-09T10:46:33Z

On Mon, Apr 08 2024 at 19:46, syzbot wrote:
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 11239 at kernel/time/hrtimer.c:1053 hrtimer_forward+0x210/0x2d0 kernel/time/hrtimer.c:1053
> RIP: 0010:hrtimer_forward+0x210/0x2d0 kernel/time/hrtimer.c:1053
> Call Trace:
> <IRQ>
> hrtimer_forward_now include/linux/hrtimer.h:355 [inline]
> mac80211_hwsim_beacon+0x192/0x1f0 drivers/net/wireless/virtual/mac80211_hwsim.c:2335
> __run_hrtimer kernel/time/hrtimer.c:1692 [inline]
> __hrtimer_run_queues+0x595/0xd00 kernel/time/hrtimer.c:1756
> hrtimer_run_softirq+0x19a/0x2c0 kernel/time/hrtimer.c:1773
> __do_softirq+0x2bc/0x943 kernel/softirq.c:554
> invoke_softirq kernel/softirq.c:428 [inline]
> __irq_exit_rcu+0xf2/0x1c0 kernel/softirq.c:633
> irq_exit_rcu+0x9/0x30 kernel/softirq.c:645
> instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
> sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1043
> </IRQ>

The code which arms the timer is not serialized against the callback so
the following can happen:

CPU1 CPU2

__run_hrtimer(timer)
if (!hrtimer_queued(timer))
hrtimer_start(timer);

hrtimer_forward(timer)
WARN_ON(hrtimer_queued(timer)

This really wants to use hrtimer_active() which takes the running
callback into account.

Thanks,

tglx

--- a/drivers/net/wireless/virtual/mac80211_hwsim.c
+++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
@@ -2422,7 +2422,7 @@ static int mac80211_hwsim_config(struct

if (!data->started || !link_data->beacon_int) {
hrtimer_cancel(&link_data->beacon_timer);
- } else if (!hrtimer_is_queued(&link_data->beacon_timer)) {
+ } else if (!hrtimer_is_active(&link_data->beacon_timer)) {
u64 tsf = mac80211_hwsim_get_tsf(hw, NULL);
u32 bcn_int = link_data->beacon_int;
u64 until_tbtt = bcn_int - do_div(tsf, bcn_int);
@@ -2517,7 +2517,7 @@ static void mac80211_hwsim_link_info_cha
info->enable_beacon, info->beacon_int);
vp->bcn_en = info->enable_beacon;
if (data->started &&
- !hrtimer_is_queued(&link_data->beacon_timer) &&
+ !hrtimer_is_active(&link_data->beacon_timer) &&
info->enable_beacon) {
u64 tsf, until_tbtt;
u32 bcn_int;