Re: [PATCH v3 4/4] sched_clock: Avoid deadlock during read from NMI

On 01/30, Daniel Thompson wrote:

@@ -98,26 +98,50 @@ unsigned long long notrace sched_clock(void) } /*

• • Updating the data required to read the clock.
• • sched_clock will never observe mis-matched data even if called from
• • an NMI. We do this by maintaining an odd/even copy of the data and
• • steering sched_clock to one or the other using a sequence counter.
• • In order to preserve the data cache profile of sched_clock as much
• • as possible the system reverts back to the even copy when the update
• • completes; the odd copy is used *only* during an update.
• */

+static void update_clock_read_data(struct clock_read_data *rd)

notrace?

+{

• /* update the backup (odd) copy with the new data */
• cd.read_data[1] = *rd;
• /* steer readers towards the new data */

s/new data/odd copy/?

• raw_write_seqcount_latch(&cd.seq);
• /* now its safe for us to update the normal (even) copy */
• cd.read_data[0] = *rd;
• /* switch readers back to the even copy */
• raw_write_seqcount_latch(&cd.seq);

+}

+/*