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authorJohn Stultz <john.stultz@linaro.org>2014-06-04 16:11:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-04 16:54:17 -0700
commit6d9bcb621b0b0a20604cbdb298c4487e44dd0da2 (patch)
treee6bb8032b8662be3551d4abcc04499c39c9e85df
parentc224815dac9c739b79050d3cc67443ff500bc478 (diff)
downloadlinux-6d9bcb621b0b0a20604cbdb298c4487e44dd0da2.tar.bz2
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 <john.stultz@linaro.org> Reported-by: Jiri Bohac <jbohac@suse.cz> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Cc: Jan Kara <jack@suse.cz> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--kernel/time/ntp.c15
-rw-r--r--kernel/time/timekeeping.c7
2 files changed, 13 insertions, 9 deletions
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 419a52cecd20..5b0ac4de3822 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);