linux-kernel - Re: [syzbot] [kernel?] WARNING in hrtimer

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Date: Tue, 09 Apr 2024 12:46:31 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: syzbot <syzbot+d1ae9c954f73570e7b58@...kaller.appspotmail.com>,
 anna-maria@...utronix.de, frederic@...nel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 syzkaller-bugs@...glegroups.com
Cc: Johannes Berg <johannes.berg@...el.com>, Kalle Valo
 <kvalo@...eaurora.org>, linux-wireless@...r.kernel.org
Subject: Re: [syzbot] [kernel?] WARNING in hrtimer_forward (2)

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;