s390/cpum_sf: Atomically reset trailer entry fields of sample-data-blocks

Ensure to reset the sample-data-block full indicator and the overflow counter
at the same time.  This must be done atomically because the sampling hardware
is still active while full sample-data-block is processed.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index ea1656073dac..9202f2858894 100644
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -953,7 +953,7 @@ static void hw_perf_event_update(struct perf_event *event, int flush_all)
         struct hw_perf_event *hwc = &event->hw;
         struct hws_trailer_entry *te;
         unsigned long *sdbt;
-        unsigned long long event_overflow, sampl_overflow, num_sdb;
+        unsigned long long event_overflow, sampl_overflow, num_sdb, te_flags;
         int done;
 
         sdbt = (unsigned long *) TEAR_REG(hwc);
@@ -990,9 +990,13 @@ static void hw_perf_event_update(struct perf_event *event, int flush_all)
                 hw_collect_samples(event, sdbt, &event_overflow);
                 num_sdb++;
 
-                /* Reset trailer */
-                xchg(&te->overflow, 0);
-                xchg((unsigned char *) te, 0x40);
+                /* Reset trailer (using compare-double-and-swap) */
+                do {
+                        te_flags = te->flags & ~SDB_TE_BUFFER_FULL_MASK;
+                        te_flags |= SDB_TE_ALERT_REQ_MASK;
+                } while (!cmpxchg_double(&te->flags, &te->overflow,
+                                         te->flags, te->overflow,
+                                         te_flags, 0ULL));
 
                 /* Advance to next sample-data-block */
                 sdbt++;