From: Thomas Richter tmricht@linux.ibm.com
[ Upstream commit 0539ad0b22877225095d8adef0c376f52cc23834 ]
The s390 CPU Measurement sampling facility has an overflow condition which fires when all entries in a SBD are used. The measurement alert interrupt is triggered and reads out all samples in this SDB. It then tests the successor SDB, if this SBD is not full, the interrupt handler does not read any samples at all from this SDB The design waits for the hardware to fill this SBD and then trigger another meassurement alert interrupt.
This scheme works nicely until an perf_event_overflow() function call discards the sample due to a too high sampling rate. The interrupt handler has logic to read out a partially filled SDB when the perf event overflow condition in linux common code is met. This causes the CPUM sampling measurement hardware and the PMU device driver to operate on the same SBD's trailer entry. This should not happen.
This can be seen here using this trace: cpumsf_pmu_add: tear:0xb5286000 hw_perf_event_update: sdbt 0xb5286000 full 1 over 0 flush_all:0 hw_perf_event_update: sdbt 0xb5286008 full 0 over 0 flush_all:0 above shows 1. interrupt hw_perf_event_update: sdbt 0xb5286008 full 1 over 0 flush_all:0 hw_perf_event_update: sdbt 0xb5286008 full 0 over 0 flush_all:0 above shows 2. interrupt ... this goes on fine until... hw_perf_event_update: sdbt 0xb5286068 full 1 over 0 flush_all:0 perf_push_sample1: overflow one or more samples read from the IRQ handler are rejected by perf_event_overflow() and the IRQ handler advances to the next SDB and modifies the trailer entry of a partially filled SDB. hw_perf_event_update: sdbt 0xb5286070 full 0 over 0 flush_all:1 timestamp: 14:32:52.519953
Next time the IRQ handler is called for this SDB the trailer entry shows an overflow count of 19 missed entries. hw_perf_event_update: sdbt 0xb5286070 full 1 over 19 flush_all:1 timestamp: 14:32:52.970058
Remove access to a follow on SDB when event overflow happened.
Signed-off-by: Thomas Richter tmricht@linux.ibm.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/s390/kernel/perf_cpum_sf.c | 6 ------ 1 file changed, 6 deletions(-)
diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c index 0cf130d37a325..ed37f3092e81f 100644 --- a/arch/s390/kernel/perf_cpum_sf.c +++ b/arch/s390/kernel/perf_cpum_sf.c @@ -1282,12 +1282,6 @@ static void hw_perf_event_update(struct perf_event *event, int flush_all) */ if (flush_all && done) break; - - /* If an event overflow happened, discard samples by - * processing any remaining sample-data-blocks. - */ - if (event_overflow) - flush_all = 1; }
/* Account sample overflows in the event hardware structure */