From: John Stultz <john.stultz@linaro.org>
To: LKML <linux-kernel@vger.kernel.org>
Cc: John Stultz <john.stultz@linaro.org>, Jan Kara <jack@suse.cz>,
Peter Zijlstra <peterz@infradead.org>,
Jiri Bohac <jbohac@suse.cz>, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: [PATCH 4/4] timekeeping: Use printk_deferred when holding timekeeping seqlock
Date: Fri, 2 May 2014 15:09:18 -0700 [thread overview]
Message-ID: <1399068558-2373-5-git-send-email-john.stultz@linaro.org> (raw)
In-Reply-To: <1399068558-2373-1-git-send-email-john.stultz@linaro.org>
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.
Cc: Jan Kara <jack@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Jiri Bohac <jbohac@suse.cz>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
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 419a52c..5b0ac4d 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 f7df8ea..ffd3113 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_once_deferred(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);
--
1.9.1
next prev parent reply other threads:[~2014-05-02 22:09 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-02 22:09 [PATCH 0/4] Convert timekeeping core to use printk_deferred (v2) John Stultz
2014-05-02 22:09 ` [PATCH 1/4] printk: Re-add irqsave/restore in printk_sched John Stultz
2014-05-04 14:58 ` Jan Kara
2014-05-04 16:13 ` Peter Zijlstra
2014-05-05 20:16 ` John Stultz
2014-05-02 22:09 ` [PATCH 2/4] printk: Rename printk_sched to printk_deferred John Stultz
2014-05-02 22:09 ` [PATCH 3/4] printk: Add printk_once_deferred John Stultz
2014-05-02 22:09 ` John Stultz [this message]
2014-05-02 23:05 ` [PATCH 0/4] Convert timekeeping core to use printk_deferred (v2) Andrew Morton
2014-05-05 15:30 ` Steven Rostedt
2014-05-05 18:42 ` Steven Rostedt
2014-05-05 20:25 ` John Stultz
2014-05-05 20:15 ` John Stultz
2014-05-05 20:47 [PATCH 0/4] Convert timekeeping core to use printk_deferred (v3) John Stultz
2014-05-05 20:47 ` [PATCH 4/4] timekeeping: Use printk_deferred when holding timekeeping seqlock John Stultz
2014-05-06 21:33 George Spelvin
2014-05-12 17:49 ` John Stultz
2014-05-13 2:44 ` George Spelvin
2014-05-13 3:39 ` John Stultz
2014-05-13 5:13 ` George Spelvin
2014-05-13 12:07 ` Mathieu Desnoyers
2014-05-13 13:29 ` George Spelvin
2014-05-13 13:39 ` Mathieu Desnoyers
2014-05-13 16:18 ` George Spelvin
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