[PATCH 2/2] firewire: core: use mutex to coordinate concurrent calls to flush completions

[Takashi Sakamoto]

In current implementation, test_and_set_bit_lock() is used to mediate
concurrent calls of ohci_flush_iso_completions(). However, the ad-hoc
usage of atomic operations is not preferable.

This commit uses mutex_trylock() as the similar operations. The core
function is responsible for the mediation, instead of 1394 OHCI driver.

Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
---
 drivers/firewire/core-iso.c | 11 +++++++++--
 drivers/firewire/ohci.c     | 37 ++++++++++++++-----------------------
 include/linux/firewire.h    |  1 +
 3 files changed, 24 insertions(+), 25 deletions(-)

diff --git a/drivers/firewire/core-iso.c b/drivers/firewire/core-iso.c
index 9f41c78878ad..a5c5ef3c725d 100644
--- a/drivers/firewire/core-iso.c
+++ b/drivers/firewire/core-iso.c
@@ -157,6 +157,7 @@ struct fw_iso_context *fw_iso_context_create(struct fw_card *card,
 	ctx->callback.sc = callback;
 	ctx->callback_data = callback_data;
 	INIT_WORK(&ctx->work, flush_completions_work);
+	mutex_init(&ctx->flushing_completions_mutex);
 
 	trace_isoc_outbound_allocate(ctx, channel, speed);
 	trace_isoc_inbound_single_allocate(ctx, channel, header_size);
@@ -173,6 +174,8 @@ void fw_iso_context_destroy(struct fw_iso_context *ctx)
 	trace_isoc_inbound_multiple_destroy(ctx);
 
 	ctx->card->driver->free_iso_context(ctx);
+
+	mutex_destroy(&ctx->flushing_completions_mutex);
 }
 EXPORT_SYMBOL(fw_iso_context_destroy);
 
@@ -226,7 +229,7 @@ EXPORT_SYMBOL(fw_iso_context_queue_flush);
  * to process the context asynchronously, fw_iso_context_schedule_flush_completions() is available
  * instead.
  *
- * Context: Process context.
+ * Context: Process context due to mutex_trylock().
  */
 int fw_iso_context_flush_completions(struct fw_iso_context *ctx)
 {
@@ -234,7 +237,11 @@ int fw_iso_context_flush_completions(struct fw_iso_context *ctx)
 	trace_isoc_inbound_single_flush_completions(ctx);
 	trace_isoc_inbound_multiple_flush_completions(ctx);
 
-	return ctx->card->driver->flush_iso_completions(ctx);
+	scoped_cond_guard(mutex_try, /* nothing to do */, &ctx->flushing_completions_mutex) {
+		return ctx->card->driver->flush_iso_completions(ctx);
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL(fw_iso_context_flush_completions);
 
diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
index 02ff0363d3ad..b182998a77f4 100644
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -166,7 +166,6 @@ struct iso_context {
 	struct context context;
 	void *header;
 	size_t header_length;
-	unsigned long flushing_completions;
 	u32 mc_buffer_bus;
 	u16 mc_completed;
 	u16 last_timestamp;
@@ -3579,31 +3578,23 @@ static void ohci_flush_queue_iso(struct fw_iso_context *base)
 static int ohci_flush_iso_completions(struct fw_iso_context *base)
 {
 	struct iso_context *ctx = container_of(base, struct iso_context, base);
-	int ret = 0;
 
-	if (!test_and_set_bit_lock(0, &ctx->flushing_completions)) {
-		// Note that tasklet softIRQ is not used to process isochronous context anymore.
-		context_tasklet((unsigned long)&ctx->context);
+	// Note that tasklet softIRQ is not used to process isochronous context anymore.
+	context_tasklet((unsigned long)&ctx->context);
 
-		switch (base->type) {
-		case FW_ISO_CONTEXT_TRANSMIT:
-		case FW_ISO_CONTEXT_RECEIVE:
-			if (ctx->header_length != 0)
-				flush_iso_completions(ctx, FW_ISO_CONTEXT_COMPLETIONS_CAUSE_FLUSH);
-			break;
-		case FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL:
-			if (ctx->mc_completed != 0)
-				flush_ir_buffer_fill(ctx);
-			break;
-		default:
-			ret = -ENOSYS;
-		}
-
-		clear_bit_unlock(0, &ctx->flushing_completions);
-		smp_mb__after_atomic();
+	switch (base->type) {
+	case FW_ISO_CONTEXT_TRANSMIT:
+	case FW_ISO_CONTEXT_RECEIVE:
+		if (ctx->header_length != 0)
+			flush_iso_completions(ctx, FW_ISO_CONTEXT_COMPLETIONS_CAUSE_FLUSH);
+		return 0;
+	case FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL:
+		if (ctx->mc_completed != 0)
+			flush_ir_buffer_fill(ctx);
+		return 0;
+	default:
+		return -ENOSYS;
 	}
-
-	return ret;
 }
 
 static const struct fw_card_driver ohci_driver = {
diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index f815d12deda0..19e8c5f9537c 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -512,6 +512,7 @@ union fw_iso_callback {
 struct fw_iso_context {
 	struct fw_card *card;
 	struct work_struct work;
+	struct mutex flushing_completions_mutex;
 	int type;
 	int channel;
 	int speed;
-- 
2.43.0