summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2024-12-08 11:51:29 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2024-12-08 11:51:29 -0800
commitc25ca0c2e42c77e0241411d374d44c41e253b3f5 (patch)
treea191fd3d5ea13957c08866d054d16b85875ce205
parent84262262177b98cf4e57e8c010119576d3c6bc2b (diff)
parent76031d9536a076bf023bedbdb1b4317fc801dd67 (diff)
downloadlwn-c25ca0c2e42c77e0241411d374d44c41e253b3f5.tar.gz
lwn-c25ca0c2e42c77e0241411d374d44c41e253b3f5.zip
Merge tag 'timers_urgent_for_v6.13_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer fix from Borislav Petkov: - Handle the case where clocksources with small counter width can, in conjunction with overly long idle sleeps, falsely trigger the negative motion detection of clocksources * tag 'timers_urgent_for_v6.13_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: clocksource: Make negative motion detection more robust
-rw-r--r--include/linux/clocksource.h2
-rw-r--r--kernel/time/clocksource.c11
-rw-r--r--kernel/time/timekeeping.c6
-rw-r--r--kernel/time/timekeeping_internal.h8
4 files changed, 20 insertions, 7 deletions
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index ef1b16da6ad5..65b7c41471c3 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -49,6 +49,7 @@ struct module;
* @archdata: Optional arch-specific data
* @max_cycles: Maximum safe cycle value which won't overflow on
* multiplication
+ * @max_raw_delta: Maximum safe delta value for negative motion detection
* @name: Pointer to clocksource name
* @list: List head for registration (internal)
* @freq_khz: Clocksource frequency in khz.
@@ -109,6 +110,7 @@ struct clocksource {
struct arch_clocksource_data archdata;
#endif
u64 max_cycles;
+ u64 max_raw_delta;
const char *name;
struct list_head list;
u32 freq_khz;
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index aab6472853fa..7304d7cf47f2 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -24,7 +24,7 @@ static void clocksource_enqueue(struct clocksource *cs);
static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start, u64 end)
{
- u64 delta = clocksource_delta(end, start, cs->mask);
+ u64 delta = clocksource_delta(end, start, cs->mask, cs->max_raw_delta);
if (likely(delta < cs->max_cycles))
return clocksource_cyc2ns(delta, cs->mult, cs->shift);
@@ -993,6 +993,15 @@ static inline void clocksource_update_max_deferment(struct clocksource *cs)
cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
cs->maxadj, cs->mask,
&cs->max_cycles);
+
+ /*
+ * Threshold for detecting negative motion in clocksource_delta().
+ *
+ * Allow for 0.875 of the counter width so that overly long idle
+ * sleeps, which go slightly over mask/2, do not trigger the
+ * negative motion detection.
+ */
+ cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3);
}
static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 0ca85ff4fbb4..3d128825d343 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -755,7 +755,8 @@ static void timekeeping_forward_now(struct timekeeper *tk)
u64 cycle_now, delta;
cycle_now = tk_clock_read(&tk->tkr_mono);
- delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last, tk->tkr_mono.mask);
+ delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last, tk->tkr_mono.mask,
+ tk->tkr_mono.clock->max_raw_delta);
tk->tkr_mono.cycle_last = cycle_now;
tk->tkr_raw.cycle_last = cycle_now;
@@ -2230,7 +2231,8 @@ static bool timekeeping_advance(enum timekeeping_adv_mode mode)
return false;
offset = clocksource_delta(tk_clock_read(&tk->tkr_mono),
- tk->tkr_mono.cycle_last, tk->tkr_mono.mask);
+ tk->tkr_mono.cycle_last, tk->tkr_mono.mask,
+ tk->tkr_mono.clock->max_raw_delta);
/* Check if there's really nothing to do */
if (offset < real_tk->cycle_interval && mode == TK_ADV_TICK)
diff --git a/kernel/time/timekeeping_internal.h b/kernel/time/timekeeping_internal.h
index 63e600e943a7..8c9079108ffb 100644
--- a/kernel/time/timekeeping_internal.h
+++ b/kernel/time/timekeeping_internal.h
@@ -30,15 +30,15 @@ static inline void timekeeping_inc_mg_floor_swaps(void)
#endif
-static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)
+static inline u64 clocksource_delta(u64 now, u64 last, u64 mask, u64 max_delta)
{
u64 ret = (now - last) & mask;
/*
- * Prevent time going backwards by checking the MSB of mask in
- * the result. If set, return 0.
+ * Prevent time going backwards by checking the result against
+ * @max_delta. If greater, return 0.
*/
- return ret & ~(mask >> 1) ? 0 : ret;
+ return ret > max_delta ? 0 : ret;
}
/* Semi public for serialization of non timekeeper VDSO updates. */