5.15-stable review patch. If anyone has any objections, please let me know.
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From: Johannes Berg johannes.berg@intel.com
[ Upstream commit abe4eaa8618bb36c2b33e9cdde0499296a23448c ]
In 'basic' time-travel mode (without =inf-cpu or =ext), we still get timer interrupts. These can happen at arbitrary points in time, i.e. while in timer_read(), which pushes time forward just a little bit. Then, if we happen to get the interrupt after calculating the new time to push to, but before actually finishing that, the interrupt will set the time to a value that's incompatible with the forward, and we'll crash because time goes backwards when we do the forwarding.
Fix this by reading the time_travel_time, calculating the adjustment, and doing the adjustment all with interrupts disabled.
Reported-by: Vincent Whitchurch Vincent.Whitchurch@axis.com Signed-off-by: Johannes Berg johannes.berg@intel.com Signed-off-by: Richard Weinberger richard@nod.at Signed-off-by: Sasha Levin sashal@kernel.org --- arch/um/kernel/time.c | 32 +++++++++++++++++++++++++++----- 1 file changed, 27 insertions(+), 5 deletions(-)
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c index fddd1dec27e6..3e270da6b6f6 100644 --- a/arch/um/kernel/time.c +++ b/arch/um/kernel/time.c @@ -432,9 +432,29 @@ static void time_travel_update_time(unsigned long long next, bool idle) time_travel_del_event(&ne); }
+static void time_travel_update_time_rel(unsigned long long offs) +{ + unsigned long flags; + + /* + * Disable interrupts before calculating the new time so + * that a real timer interrupt (signal) can't happen at + * a bad time e.g. after we read time_travel_time but + * before we've completed updating the time. + */ + local_irq_save(flags); + time_travel_update_time(time_travel_time + offs, false); + local_irq_restore(flags); +} + void time_travel_ndelay(unsigned long nsec) { - time_travel_update_time(time_travel_time + nsec, false); + /* + * Not strictly needed to use _rel() version since this is + * only used in INFCPU/EXT modes, but it doesn't hurt and + * is more readable too. + */ + time_travel_update_time_rel(nsec); } EXPORT_SYMBOL(time_travel_ndelay);
@@ -568,7 +588,11 @@ static void time_travel_set_start(void) #define time_travel_time 0 #define time_travel_ext_waiting 0
-static inline void time_travel_update_time(unsigned long long ns, bool retearly) +static inline void time_travel_update_time(unsigned long long ns, bool idle) +{ +} + +static inline void time_travel_update_time_rel(unsigned long long offs) { }
@@ -720,9 +744,7 @@ static u64 timer_read(struct clocksource *cs) */ if (!irqs_disabled() && !in_interrupt() && !in_softirq() && !time_travel_ext_waiting) - time_travel_update_time(time_travel_time + - TIMER_MULTIPLIER, - false); + time_travel_update_time_rel(TIMER_MULTIPLIER); return time_travel_time / TIMER_MULTIPLIER; }