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authorJohn Stultz <john.stultz@linaro.org>2013-09-11 16:50:56 -0700
committerIngo Molnar <mingo@kernel.org>2013-09-12 07:49:51 +0200
commit7bd36014460f793c19e7d6c94dab67b0afcfcb7f (patch)
treeaff35c1d376508c4436591df0895111c73cc75b8
parent5a8e01f8fa51f5cbce8f37acc050eb2319d12956 (diff)
downloadop-kernel-dev-7bd36014460f793c19e7d6c94dab67b0afcfcb7f.zip
op-kernel-dev-7bd36014460f793c19e7d6c94dab67b0afcfcb7f.tar.gz
timekeeping: Fix HRTICK related deadlock from ntp lock changes
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> Cc: stable <stable@vger.kernel.org> #3.11, 3.10 Link: http://lkml.kernel.org/r/1378943457-27314-1-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--include/linux/timex.h1
-rw-r--r--kernel/time/ntp.c6
-rw-r--r--kernel/time/timekeeping.c2
3 files changed, 5 insertions, 4 deletions
diff --git a/include/linux/timex.h b/include/linux/timex.h
index b3726e6..dd3edd7 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -141,6 +141,7 @@ extern int do_adjtimex(struct timex *);
extern void hardpps(const struct timespec *, const struct timespec *);
int read_current_timer(unsigned long *timer_val);
+void ntp_notify_cmos_timer(void);
/* The clock frequency of the i8253/i8254 PIT */
#define PIT_TICK_RATE 1193182ul
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 8f5b3b9..bb22151 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 48b9fff..947ba25 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1703,6 +1703,8 @@ int do_adjtimex(struct timex *txc)
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
+ ntp_notify_cmos_timer();
+
return ret;
}
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