Subject: [to-be-updated] timekeeping-use-printk_deferred-when-holding-timekeeping-seqlock.patch removed from -mm tree
To: john.stultz@xxxxxxxxxx,jack@xxxxxxx,jbohac@xxxxxxx,mingo@xxxxxxxxxx,peterz@xxxxxxxxxxxxx,rostedt@xxxxxxxxxxx,tglx@xxxxxxxxxxxxx,mm-commits@xxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Mon, 05 May 2014 15:05:04 -0700
The patch titled
Subject: timekeeping: use printk_deferred() when holding timekeeping seqlock
has been removed from the -mm tree. Its filename was
timekeeping-use-printk_deferred-when-holding-timekeeping-seqlock.patch
This patch was dropped because an updated version will be merged
------------------------------------------------------
From: John Stultz <john.stultz@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx>
Reported-by: Jiri Bohac <jbohac@xxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/time/ntp.c | 15 +++++++++------
kernel/time/timekeeping.c | 7 ++++---
2 files changed, 13 insertions(+), 9 deletions(-)
diff -puN kernel/time/ntp.c~timekeeping-use-printk_deferred-when-holding-timekeeping-seqlock kernel/time/ntp.c
--- a/kernel/time/ntp.c~timekeeping-use-printk_deferred-when-holding-timekeeping-seqlock
+++ a/kernel/time/ntp.c
@@ -786,8 +786,9 @@ static long hardpps_update_freq(struct p
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 p
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 er
* 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 *ph
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 -puN kernel/time/timekeeping.c~timekeeping-use-printk_deferred-when-holding-timekeeping-seqlock kernel/time/timekeeping.c
--- a/kernel/time/timekeeping.c~timekeeping-use-printk_deferred-when-holding-timekeeping-seqlock
+++ a/kernel/time/timekeeping.c
@@ -852,8 +852,9 @@ static void __timekeeping_inject_sleepti
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 ti
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);
_
Patches currently in -mm which might be from john.stultz@xxxxxxxxxx are
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