[S390] qdio: prevent race for shared indicators
If the shared indicator is used the following race leads to
an inbound stall:
Device CPU0 CPU1
========================================================
non-shared DSCI =>1
ALSI => 1
Thin INT
ALSI => 0
non-shared DSCI
tasklets scheduled
shared DSCI => 1
ALSI => 1
shared DSCI => 0
ALSI ? -> set
Thin INT
ALSI => 0
ALSI was set,
shared DSCI => 1
After that no more interrupts occur because the DSCI is still set.
Fix that race by only resetting the shared DSCI if it was actually
set so the tasklets for all shared devices are scheduled and will
run after the interrupt.
Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/cio/qdio_thinint.c b/drivers/s390/cio/qdio_thinint.c
index 64b59a5..5c4e741 100644
--- a/drivers/s390/cio/qdio_thinint.c
+++ b/drivers/s390/cio/qdio_thinint.c
@@ -36,22 +36,8 @@
struct indicator_t *q_indicators;
-static int css_qdio_omit_svs;
-
static u64 last_ai_time;
-static inline unsigned long do_clear_global_summary(void)
-{
- register unsigned long __fn asm("1") = 3;
- register unsigned long __tmp asm("2");
- register unsigned long __time asm("3");
-
- asm volatile(
- " .insn rre,0xb2650000,2,0"
- : "+d" (__fn), "=d" (__tmp), "=d" (__time));
- return __time;
-}
-
/* returns addr for the device state change indicator */
static u32 *get_indicator(void)
{
@@ -84,10 +70,6 @@
struct qdio_q *q;
int i;
- /* No TDD facility? If we must use SIGA-s we can also omit SVS. */
- if (!css_qdio_omit_svs && irq_ptr->siga_flag.sync)
- css_qdio_omit_svs = 1;
-
mutex_lock(&tiq_list_lock);
for_each_input_queue(irq_ptr, q, i)
list_add_rcu(&q->entry, &tiq_list);
@@ -113,9 +95,9 @@
}
}
-static inline int shared_ind_used(void)
+static inline u32 shared_ind_set(void)
{
- return atomic_read(&q_indicators[TIQDIO_SHARED_IND].count);
+ return q_indicators[TIQDIO_SHARED_IND].ind;
}
/**
@@ -125,22 +107,12 @@
*/
static void tiqdio_thinint_handler(void *alsi, void *data)
{
+ u32 si_used = shared_ind_set();
struct qdio_q *q;
last_ai_time = S390_lowcore.int_clock;
kstat_cpu(smp_processor_id()).irqs[IOINT_QAI]++;
- /*
- * SVS only when needed: issue SVS to benefit from iqdio interrupt
- * avoidance (SVS clears adapter interrupt suppression overwrite).
- */
- if (!css_qdio_omit_svs)
- do_clear_global_summary();
-
- /* reset local summary indicator */
- if (shared_ind_used())
- xchg(tiqdio_alsi, 0);
-
/* protect tiq_list entries, only changed in activate or shutdown */
rcu_read_lock();
@@ -148,7 +120,10 @@
list_for_each_entry_rcu(q, &tiq_list, entry) {
/* only process queues from changed sets */
- if (!*q->irq_ptr->dsci)
+ if (unlikely(shared_ind(q->irq_ptr->dsci))) {
+ if (!si_used)
+ continue;
+ } else if (!*q->irq_ptr->dsci)
continue;
if (q->u.in.queue_start_poll) {
@@ -164,7 +139,7 @@
q->irq_ptr->int_parm);
} else {
/* only clear it if the indicator is non-shared */
- if (!shared_ind(q->irq_ptr))
+ if (!shared_ind(q->irq_ptr->dsci))
xchg(q->irq_ptr->dsci, 0);
/*
* Call inbound processing but not directly
@@ -180,13 +155,8 @@
* If the shared indicator was used clear it now after all queues
* were processed.
*/
- if (shared_ind_used()) {
+ if (si_used && shared_ind_set())
xchg(&q_indicators[TIQDIO_SHARED_IND].ind, 0);
-
- /* prevent racing */
- if (*tiqdio_alsi)
- xchg(&q_indicators[TIQDIO_SHARED_IND].ind, 1 << 7);
- }
}
static int set_subchannel_ind(struct qdio_irq *irq_ptr, int reset)
@@ -271,12 +241,6 @@
{
if (!is_thinint_irq(irq_ptr))
return 0;
-
- /* Check for aif time delay disablement. If installed,
- * omit SVS even under LPAR
- */
- if (css_general_characteristics.aif_tdd)
- css_qdio_omit_svs = 1;
return set_subchannel_ind(irq_ptr, 0);
}