From c6042d891e071eb7d8f116f35f75aa6b6d774757 Mon Sep 17 00:00:00 2001 From: John Stultz Date: Wed, 14 May 2014 10:02:28 +1000 Subject: [PATCH] timekeeping: use printk_deferred when holding timekeeping seqlock Jiri Bohac pointed out that there are rare but potential deadlock possibilities when calling printk while holding the timekeeping seqlock. This is due to printk() triggering console sem wakeup, which can cause scheduling code to trigger hrtimers which may try to read the time. Specifically, as Jiri pointed out, that path is: printk vprintk_emit console_unlock up(&console_sem) __up wake_up_process try_to_wake_up ttwu_do_activate ttwu_activate activate_task enqueue_task enqueue_task_fair hrtick_update hrtick_start_fair hrtick_start_fair get_time ktime_get --> endless loop on read_seqcount_retry(&timekeeper_seq, ...) This patch tries to avoid this issue by using printk_deferred (previously named printk_sched) which should defer printing via a irq_work_queue. Signed-off-by: John Stultz Reported-by: Jiri Bohac Reviewed-by: Steven Rostedt Cc: Jan Kara Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Steven Rostedt Signed-off-by: Andrew Morton --- kernel/time/ntp.c | 15 +++++++++------ kernel/time/timekeeping.c | 7 ++++--- 2 files changed, 13 insertions(+), 9 deletions(-) diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index 82b7c9edba7e..3c6cb3116467 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -786,8 +786,9 @@ static long hardpps_update_freq(struct pps_normtime freq_norm) time_status |= STA_PPSERROR; pps_errcnt++; pps_dec_freq_interval(); - pr_err("hardpps: PPSERROR: interval too long - %ld s\n", - freq_norm.sec); + printk_deferred(KERN_ERR + "hardpps: PPSERROR: interval too long - %ld s\n", + freq_norm.sec); return 0; } @@ -800,7 +801,8 @@ static long hardpps_update_freq(struct pps_normtime freq_norm) delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT); pps_freq = ftemp; if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) { - pr_warning("hardpps: PPSWANDER: change=%ld\n", delta); + printk_deferred(KERN_WARNING + "hardpps: PPSWANDER: change=%ld\n", delta); time_status |= STA_PPSWANDER; pps_stbcnt++; pps_dec_freq_interval(); @@ -844,8 +846,9 @@ static void hardpps_update_phase(long error) * the time offset is updated. */ if (jitter > (pps_jitter << PPS_POPCORN)) { - pr_warning("hardpps: PPSJITTER: jitter=%ld, limit=%ld\n", - jitter, (pps_jitter << PPS_POPCORN)); + printk_deferred(KERN_WARNING + "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n", + jitter, (pps_jitter << PPS_POPCORN)); time_status |= STA_PPSJITTER; pps_jitcnt++; } else if (time_status & STA_PPSTIME) { @@ -902,7 +905,7 @@ void __hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts) time_status |= STA_PPSJITTER; /* restart the frequency calibration interval */ pps_fbase = *raw_ts; - pr_err("hardpps: PPSJITTER: bad pulse\n"); + printk_deferred(KERN_ERR "hardpps: PPSJITTER: bad pulse\n"); return; } diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index f7df8ea21707..32d8d6aaedb8 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -852,8 +852,9 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk, struct timespec *delta) { if (!timespec_valid_strict(delta)) { - printk(KERN_WARNING "__timekeeping_inject_sleeptime: Invalid " - "sleep delta value!\n"); + printk_deferred(KERN_WARNING + "__timekeeping_inject_sleeptime: Invalid " + "sleep delta value!\n"); return; } tk_xtime_add(tk, delta); @@ -1157,7 +1158,7 @@ static void timekeeping_adjust(struct timekeeper *tk, s64 offset) if (unlikely(tk->clock->maxadj && (tk->mult + adj > tk->clock->mult + tk->clock->maxadj))) { - printk_once(KERN_WARNING + printk_deferred_once(KERN_WARNING "Adjusting %s more than 11%% (%ld vs %ld)\n", tk->clock->name, (long)tk->mult + adj, (long)tk->clock->mult + tk->clock->maxadj); -- 2.39.5