Revert "firewire: core: use mutex to coordinate concurrent calls to flush completions"

This reverts commit d9605d67562505e27dcc0f71af418118d3db91e5, since this
commit is on the following reverted changes.

Link: https://lore.kernel.org/r/20240912133038.238786-2-o-takashi@sakamocchi.jpSigned-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

drivers/firewire/core-iso.c

@@ -157,7 +157,6 @@ 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);
@@ -174,8 +173,6 @@ 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);
 
@@ -229,7 +226,7 @@ EXPORT_SYMBOL(fw_iso_context_queue_flush);
  * to process the context asynchronously, fw_iso_context_schedule_flush_completions() is available
  * instead.
  *
- * Context: Process context due to mutex_trylock().
+ * Context: Process context.
  */
 int fw_iso_context_flush_completions(struct fw_iso_context *ctx)
 {
@@ -237,11 +234,7 @@ 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);
 
-	scoped_cond_guard(mutex_try, /* nothing to do */, &ctx->flushing_completions_mutex) {
-		return ctx->card->driver->flush_iso_completions(ctx);
-	}
-
-	return 0;
+	return ctx->card->driver->flush_iso_completions(ctx);
 }
 EXPORT_SYMBOL(fw_iso_context_flush_completions);
 

drivers/firewire/ohci.c

@@ -166,6 +166,7 @@ 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;
@@ -3578,23 +3579,31 @@ 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;
 
-	// Note that tasklet softIRQ is not used to process isochronous context anymore.
-	context_tasklet((unsigned long)&ctx->context);
+	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);
 
-	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;
+		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();
 	}
+
+	return ret;
 }
 
 static const struct fw_card_driver ohci_driver = {

include/linux/firewire.h

@@ -512,7 +512,6 @@ 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;