mtip32xx: mtip_async_complete() bug fixes

This patch fixes 2 issues in the fast completion path:
1) Possible double completions / double dma_unmap_sg() calls due to lack
of atomicity in the check and subsequent dereference of the upper layer
callback function. Fixed with cmpxchg before unmap and callback.
2) Regression in unaligned IO constraining workaround for p420m devices.
Fixed by checking if IO is unaligned and using proper semaphore if so.
Signed-off-by: Sam Bradshaw <sbradshaw@micron.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/mtip32xx/mtip32xx.c

@@ -252,38 +252,45 @@ static void mtip_async_complete(struct mtip_port *port,
 				void *data,
 				int status)
 {
-	struct mtip_cmd *command;
+	struct mtip_cmd *cmd;
 	struct driver_data *dd = data;
-	int cb_status = status ? -EIO : 0;
+	int unaligned, cb_status = status ? -EIO : 0;
+	void (*func)(void *, int);
 
 	if (unlikely(!dd) || unlikely(!port))
 		return;
 
-	command = &port->commands[tag];
+	cmd = &port->commands[tag];
 
 	if (unlikely(status == PORT_IRQ_TF_ERR)) {
 		dev_warn(&port->dd->pdev->dev,
 			"Command tag %d failed due to TFE\n", tag);
 	}
 
-	/* Unmap the DMA scatter list entries */
-	dma_unmap_sg(&dd->pdev->dev,
-		command->sg,
-		command->scatter_ents,
-		command->direction);
+	/* Clear the active flag */
+	atomic_set(&port->commands[tag].active, 0);
 
 	/* Upper layer callback */
-	if (likely(command->async_callback))
-		command->async_callback(command->async_data, cb_status);
+	func = cmd->async_callback;
+	if (likely(func && cmpxchg(&cmd->async_callback, func, 0) == func)) {
 
-	command->async_callback = NULL;
-	command->comp_func = NULL;
+		/* Unmap the DMA scatter list entries */
+		dma_unmap_sg(&dd->pdev->dev,
+			cmd->sg,
+			cmd->scatter_ents,
+			cmd->direction);
 
-	/* Clear the allocated and active bits for the command */
-	atomic_set(&port->commands[tag].active, 0);
+		func(cmd->async_data, cb_status);
+		unaligned = cmd->unaligned;
+
+		/* Clear the allocated bit for the command */
 		release_slot(port, tag);
 
+		if (unlikely(unaligned))
+			up(&port->cmd_slot_unal);
+		else
 			up(&port->cmd_slot);
+	}
 }
 
 /*
@@ -660,11 +667,12 @@ static void mtip_timeout_function(unsigned long int data)
 {
 	struct mtip_port *port = (struct mtip_port *) data;
 	struct host_to_dev_fis *fis;
-	struct mtip_cmd *command;
-	int tag, cmdto_cnt = 0;
+	struct mtip_cmd *cmd;
+	int unaligned, tag, cmdto_cnt = 0;
 	unsigned int bit, group;
 	unsigned int num_command_slots;
 	unsigned long to, tagaccum[SLOTBITS_IN_LONGS];
+	void (*func)(void *, int);
 
 	if (unlikely(!port))
 		return;
@@ -694,8 +702,8 @@ static void mtip_timeout_function(unsigned long int data)
 			group = tag >> 5;
 			bit = tag & 0x1F;
 
-			command = &port->commands[tag];
-			fis = (struct host_to_dev_fis *) command->command;
+			cmd = &port->commands[tag];
+			fis = (struct host_to_dev_fis *) cmd->command;
 
 			set_bit(tag, tagaccum);
 			cmdto_cnt++;
@@ -709,29 +717,32 @@ static void mtip_timeout_function(unsigned long int data)
 			 */
 			writel(1 << bit, port->completed[group]);
 
+			/* Clear the active flag for the command */
+			atomic_set(&port->commands[tag].active, 0);
+
+			func = cmd->async_callback;
+			if (func &&
+			    cmpxchg(&cmd->async_callback, func, 0) == func) {
+
 				/* Unmap the DMA scatter list entries */
 				dma_unmap_sg(&port->dd->pdev->dev,
-					command->sg,
-					command->scatter_ents,
-					command->direction);
-
-			/* Call the async completion callback. */
-			if (likely(command->async_callback))
-				command->async_callback(command->async_data,
-							 -EIO);
-			command->async_callback = NULL;
-			command->comp_func = NULL;
+						cmd->sg,
+						cmd->scatter_ents,
+						cmd->direction);
 
-			/*
-			 * Clear the allocated bit and active tag for the
-			 * command.
-			 */
-			atomic_set(&port->commands[tag].active, 0);
+				func(cmd->async_data, -EIO);
+				unaligned = cmd->unaligned;
+
+				/* Clear the allocated bit for the command. */
 				release_slot(port, tag);
 
+				if (unaligned)
+					up(&port->cmd_slot_unal);
+				else
 					up(&port->cmd_slot);
 			}
 		}
+	}
 
 	if (cmdto_cnt) {
 		print_tags(port->dd, "timed out", tagaccum, cmdto_cnt);

drivers/block/mtip32xx/mtip32xx.h

@@ -92,7 +92,7 @@
 
 /* Driver name and version strings */
 #define MTIP_DRV_NAME		"mtip32xx"
-#define MTIP_DRV_VERSION	"1.3.0"
+#define MTIP_DRV_VERSION	"1.3.1"
 
 /* Maximum number of minor device numbers per device. */
 #define MTIP_MAX_MINORS		16