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authorJohn Stultz <john.stultz@linaro.org>2013-09-11 16:50:56 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-10-01 09:17:45 -0700
commit63946e8616205dafe39b4d88f9fc3dc7c4fd79aa (patch)
treee1f6377f19f8fd692376a336713f99dc0ac93344 /kernel/time
parentbeb6f0e8d246adca601d786d206d414d1d0a549b (diff)
downloadlinaro-lsk-63946e8616205dafe39b4d88f9fc3dc7c4fd79aa.tar.gz
timekeeping: Fix HRTICK related deadlock from ntp lock changes
commit 7bd36014460f793c19e7d6c94dab67b0afcfcb7f upstream. Gerlando Falauto reported that when HRTICK is enabled, it is possible to trigger system deadlocks. These were hard to reproduce, as HRTICK has been broken in the past, but seemed to be connected to the timekeeping_seq lock. Since seqlock/seqcount's aren't supported w/ lockdep, I added some extra spinlock based locking and triggered the following lockdep output: [ 15.849182] ntpd/4062 is trying to acquire lock: [ 15.849765] (&(&pool->lock)->rlock){..-...}, at: [<ffffffff810aa9b5>] __queue_work+0x145/0x480 [ 15.850051] [ 15.850051] but task is already holding lock: [ 15.850051] (timekeeper_lock){-.-.-.}, at: [<ffffffff810df6df>] do_adjtimex+0x7f/0x100 <snip> [ 15.850051] Chain exists of: &(&pool->lock)->rlock --> &p->pi_lock --> timekeeper_lock [ 15.850051] Possible unsafe locking scenario: [ 15.850051] [ 15.850051] CPU0 CPU1 [ 15.850051] ---- ---- [ 15.850051] lock(timekeeper_lock); [ 15.850051] lock(&p->pi_lock); [ 15.850051] lock(timekeeper_lock); [ 15.850051] lock(&(&pool->lock)->rlock); [ 15.850051] [ 15.850051] *** DEADLOCK *** The deadlock was introduced by 06c017fdd4dc48451a ("timekeeping: Hold timekeepering locks in do_adjtimex and hardpps") in 3.10 This patch avoids this deadlock, by moving the call to schedule_delayed_work() outside of the timekeeper lock critical section. Reported-by: Gerlando Falauto <gerlando.falauto@keymile.com> Tested-by: Lin Ming <minggr@gmail.com> Signed-off-by: John Stultz <john.stultz@linaro.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Link: http://lkml.kernel.org/r/1378943457-27314-1-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/ntp.c6
-rw-r--r--kernel/time/timekeeping.c2
2 files changed, 4 insertions, 4 deletions
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 8f5b3b98577..bb2215174f0 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -516,13 +516,13 @@ static void sync_cmos_clock(struct work_struct *work)
schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
}
-static void notify_cmos_timer(void)
+void ntp_notify_cmos_timer(void)
{
schedule_delayed_work(&sync_cmos_work, 0);
}
#else
-static inline void notify_cmos_timer(void) { }
+void ntp_notify_cmos_timer(void) { }
#endif
@@ -687,8 +687,6 @@ int __do_adjtimex(struct timex *txc, struct timespec *ts, s32 *time_tai)
if (!(time_status & STA_NANO))
txc->time.tv_usec /= NSEC_PER_USEC;
- notify_cmos_timer();
-
return result;
}
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index baeeb5c87cf..fcc261c5df2 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1682,6 +1682,8 @@ int do_adjtimex(struct timex *txc)
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
+ ntp_notify_cmos_timer();
+
return ret;
}