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s390/time: fix clocksource steering for negative clock offsets 

The TOD clock offset injected by an STP sync check can be negative.
If the resulting total tod_steering_delta gets negative the kernel
will panic.

Change the type of tod_steering_delta to a signed type.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 75c7b6f3f6 ("s390/time: steer clocksource on STP sync events")
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2016-11-16 16:36:26 +01:00
parent 68962269a4
commit 191ce9d1fd
1 changed files with 3 additions and 4 deletions
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7
arch/s390/kernel/time.c
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@ -63,7 +63,7 @@ unsigned char ptff_function_mask[16];
static unsigned long long lpar_offset; static unsigned long long lpar_offset;
static unsigned long long initial_leap_seconds; static unsigned long long initial_leap_seconds;
static unsigned long long tod_steering_end; static unsigned long long tod_steering_end;
static unsigned long long tod_steering_delta; static long long tod_steering_delta;
/* /*
* Get time offsets with PTFF * Get time offsets with PTFF
@ -223,8 +223,7 @@ static cycle_t read_tod_clock(struct clocksource *cs)
* therefore steered in ~9h. The adjust will decrease * therefore steered in ~9h. The adjust will decrease
* over time, until it finally reaches 0. * over time, until it finally reaches 0.
*/ */
now += ((s64) tod_steering_delta < 0) ? now += (tod_steering_delta < 0) ? (adj >> 15) : -(adj >> 15);
(adj >> 15) : -(adj >> 15);
preempt_enable(); preempt_enable();
return now; return now;
} }
@ -412,7 +411,7 @@ static void clock_sync_global(unsigned long long delta)
adj = tod_steering_end - now; adj = tod_steering_end - now;
if (unlikely((s64) adj >= 0)) if (unlikely((s64) adj >= 0))
/* Calculate how much of the old adjustment is left. */ /* Calculate how much of the old adjustment is left. */
tod_steering_delta = ((s64) tod_steering_delta < 0) ? tod_steering_delta = (tod_steering_delta < 0) ?
-(adj >> 15) : (adj >> 15); -(adj >> 15) : (adj >> 15);
tod_steering_delta += delta; tod_steering_delta += delta;
if ((abs(tod_steering_delta) >> 48) != 0) if ((abs(tod_steering_delta) >> 48) != 0)