| From b19ec117ebeaff3a852abb1a56dbceb5b8d882ab Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Wed, 15 Sep 2021 11:29:37 +0200 |
| Subject: mac80211-hwsim: fix late beacon hrtimer handling |
| |
| From: Johannes Berg <johannes.berg@intel.com> |
| |
| [ Upstream commit 313bbd1990b6ddfdaa7da098d0c56b098a833572 ] |
| |
| Thomas explained in https://lore.kernel.org/r/87mtoeb4hb.ffs@tglx |
| that our handling of the hrtimer here is wrong: If the timer fires |
| late (e.g. due to vCPU scheduling, as reported by Dmitry/syzbot) |
| then it tries to actually rearm the timer at the next deadline, |
| which might be in the past already: |
| |
| 1 2 3 N N+1 |
| | | | ... | | |
| |
| ^ intended to fire here (1) |
| ^ next deadline here (2) |
| ^ actually fired here |
| |
| The next time it fires, it's later, but will still try to schedule |
| for the next deadline (now 3), etc. until it catches up with N, |
| but that might take a long time, causing stalls etc. |
| |
| Now, all of this is simulation, so we just have to fix it, but |
| note that the behaviour is wrong even per spec, since there's no |
| value then in sending all those beacons unaligned - they should be |
| aligned to the TBTT (1, 2, 3, ... in the picture), and if we're a |
| bit (or a lot) late, then just resume at that point. |
| |
| Therefore, change the code to use hrtimer_forward_now() which will |
| ensure that the next firing of the timer would be at N+1 (in the |
| picture), i.e. the next interval point after the current time. |
| |
| Suggested-by: Thomas Gleixner <tglx@linutronix.de> |
| Reported-by: Dmitry Vyukov <dvyukov@google.com> |
| Reported-by: syzbot+0e964fad69a9c462bc1e@syzkaller.appspotmail.com |
| Fixes: 01e59e467ecf ("mac80211_hwsim: hrtimer beacon") |
| Reviewed-by: Thomas Gleixner <tglx@linutronix.de> |
| Link: https://lore.kernel.org/r/20210915112936.544f383472eb.I3f9712009027aa09244b65399bf18bf482a8c4f1@changeid |
| Signed-off-by: Johannes Berg <johannes.berg@intel.com> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| drivers/net/wireless/mac80211_hwsim.c | 4 ++-- |
| 1 file changed, 2 insertions(+), 2 deletions(-) |
| |
| diff --git a/drivers/net/wireless/mac80211_hwsim.c b/drivers/net/wireless/mac80211_hwsim.c |
| index 4ca0b06d09ad..b793d61d15d2 100644 |
| --- a/drivers/net/wireless/mac80211_hwsim.c |
| +++ b/drivers/net/wireless/mac80211_hwsim.c |
| @@ -1795,8 +1795,8 @@ mac80211_hwsim_beacon(struct hrtimer *timer) |
| bcn_int -= data->bcn_delta; |
| data->bcn_delta = 0; |
| } |
| - hrtimer_forward(&data->beacon_timer, hrtimer_get_expires(timer), |
| - ns_to_ktime(bcn_int * NSEC_PER_USEC)); |
| + hrtimer_forward_now(&data->beacon_timer, |
| + ns_to_ktime(bcn_int * NSEC_PER_USEC)); |
| return HRTIMER_RESTART; |
| } |
| |
| -- |
| 2.33.0 |
| |