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Commit 1b44e98d authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Linus Torvalds
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[PATCH] s390: stop_hz_timer vs. xtime updates 



The calculation of the value return by next_timer_interrupt from jiffies to
jiffies_64 is racy against xtime updates.  We need to protect the calculation
with read_seqbegin/read_seqretry.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e1c3ad96

arch/s390/kernel/time.c

+7 −1
Original line number Diff line number Diff line
@@ -237,6 +237,8 @@ int sysctl_hz_timer = 1; 
 */

static inline void stop_hz_timer(void)

{

	unsigned long flags;

	unsigned long seq, next;

	__u64 timer, todval;



	if (sysctl_hz_timer != 0)
@@ -257,7 +259,11 @@ static inline void stop_hz_timer(void) 
	 * This cpu is going really idle. Set up the clock comparator

	 * for the next event.

	 */

	timer = (__u64) (next_timer_interrupt() - jiffies) + jiffies_64;

	next = next_timer_interrupt();

	do {

		seq = read_seqbegin_irqsave(&xtime_lock, flags);

		timer = (__u64)(next - jiffies) + jiffies_64;

	} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));

	todval = -1ULL;

	/* Be careful about overflows. */

	if (timer < (-1ULL / CLK_TICKS_PER_JIFFY)) {