The patch titled
posix-cpu-timers: prevent signal delivery starvation
has been added to the -mm tree. Its filename is
posix-cpu-timers-prevent-signal-delivery-starvation.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: posix-cpu-timers: prevent signal delivery starvation
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
The integer divisions in the timer accounting code can round the result
down to 0. Adding 0 is without effect and the signal delivery stops.
Clamp the division result to minimum 1 to avoid this.
Problem was reported by Seongbae Park <spark@xxxxxxxxxx>, who provided
also an inital patch.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: Daniel Walker <dwalker@xxxxxxxxxx>
Cc: Toyo Abe <toyoa@xxxxxxxxxx>
Cc: john stultz <johnstul@xxxxxxxxxx>
Cc: Roman Zippel <zippel@xxxxxxxxxxxxxx>
Cc: Seongbae Park <spark@xxxxxxxxxx>
Cc: Peter Mattis <pmattis@xxxxxxxxxx>
Cc: Rohit Seth <rohitseth@xxxxxxxxxx>
Cc: Martin Bligh <mbligh@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/posix-cpu-timers.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
diff -puN kernel/posix-cpu-timers.c~posix-cpu-timers-prevent-signal-delivery-starvation kernel/posix-cpu-timers.c
--- a/kernel/posix-cpu-timers.c~posix-cpu-timers-prevent-signal-delivery-starvation
+++ a/kernel/posix-cpu-timers.c
@@ -88,6 +88,19 @@ static inline union cpu_time_count cpu_t
}
/*
+ * Divide and limit the result to res >= 1
+ *
+ * This is necessary to prevent signal delivery starvation, when the result of
+ * the division would be rounded down to 0.
+ */
+static inline cputime_t cputime_div_min(cputime_t time, unsigned long div)
+{
+ cputime_t res = cputime_div(time, div);
+
+ return min_t(cputime_t, res, 1);
+}
+
+/*
* Update expiry time from increment, and increase overrun count,
* given the current clock sample.
*/
@@ -483,8 +496,8 @@ static void process_timer_rebalance(stru
BUG();
break;
case CPUCLOCK_PROF:
- left = cputime_div(cputime_sub(expires.cpu, val.cpu),
- nthreads);
+ left = cputime_div_min(cputime_sub(expires.cpu, val.cpu),
+ nthreads);
do {
if (likely(!(t->flags & PF_EXITING))) {
ticks = cputime_add(prof_ticks(t), left);
@@ -498,8 +511,8 @@ static void process_timer_rebalance(stru
} while (t != p);
break;
case CPUCLOCK_VIRT:
- left = cputime_div(cputime_sub(expires.cpu, val.cpu),
- nthreads);
+ left = cputime_div_min(cputime_sub(expires.cpu, val.cpu),
+ nthreads);
do {
if (likely(!(t->flags & PF_EXITING))) {
ticks = cputime_add(virt_ticks(t), left);
@@ -515,6 +528,7 @@ static void process_timer_rebalance(stru
case CPUCLOCK_SCHED:
nsleft = expires.sched - val.sched;
do_div(nsleft, nthreads);
+ nsleft = min_t(unsigned long long, nsleft, 1);
do {
if (likely(!(t->flags & PF_EXITING))) {
ns = t->sched_time + nsleft;
@@ -1159,12 +1173,13 @@ static void check_process_timers(struct
prof_left = cputime_sub(prof_expires, utime);
prof_left = cputime_sub(prof_left, stime);
- prof_left = cputime_div(prof_left, nthreads);
+ prof_left = cputime_div_min(prof_left, nthreads);
virt_left = cputime_sub(virt_expires, utime);
- virt_left = cputime_div(virt_left, nthreads);
+ virt_left = cputime_div_min(virt_left, nthreads);
if (sched_expires) {
sched_left = sched_expires - sched_time;
do_div(sched_left, nthreads);
+ sched_left = min_t(unsigned long long, sched_left, 1);
} else {
sched_left = 0;
}
_
Patches currently in -mm which might be from tglx@xxxxxxxxxxxxx are
posix-cpu-timers-prevent-signal-delivery-starvation.patch
gtod-exponential-update_wall_time.patch
gtod-persistent-clock-support-core.patch
gtod-persistent-clock-support-i386.patch
time-uninline-jiffiesh.patch
time-fix-msecs_to_jiffies-bug.patch
time-fix-timeout-overflow.patch
cleanup-uninline-irq_enter-and-move-it-into-a-function.patch
dynticks-extend-next_timer_interrupt-to-use-a-reference-jiffie.patch
hrtimers-namespace-and-enum-cleanup.patch
hrtimers-clean-up-locking.patch
hrtimers-state-tracking.patch
hrtimers-clean-up-callback-tracking.patch
hrtimers-move-and-add-documentation.patch
clockevents-core.patch
clockevents-drivers-for-i386.patch
high-res-timers-core.patch
gtod-mark-tsc-unusable-for-highres-timers.patch
dynticks-core.patch
dynticks-add-nohz-stats-to-proc-stat.patch
dynticks-i386-arch-code.patch
high-res-timers-dynticks-enable-i386-support.patch
debugging-feature-timer-stats.patch
-
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