diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2024-12-08 11:51:29 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2024-12-08 11:51:29 -0800 |
commit | c25ca0c2e42c77e0241411d374d44c41e253b3f5 (patch) | |
tree | a191fd3d5ea13957c08866d054d16b85875ce205 /kernel | |
parent | 84262262177b98cf4e57e8c010119576d3c6bc2b (diff) | |
parent | 76031d9536a076bf023bedbdb1b4317fc801dd67 (diff) |
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
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/time/clocksource.c | 11 | ||||
-rw-r--r-- | kernel/time/timekeeping.c | 6 | ||||
-rw-r--r-- | kernel/time/timekeeping_internal.h | 8 |
3 files changed, 18 insertions, 7 deletions
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. */ |