Patch "scsi: hisi_sas: fix the risk of freeing slot twice" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

scsi: hisi_sas: fix the risk of freeing slot twice

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
scsi-hisi_sas-fix-the-risk-of-freeing-slot-twice.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Xiaofei Tan <[email protected]>
Date: Tue, 24 Oct 2017 23:51:38 +0800
Subject: scsi: hisi_sas: fix the risk of freeing slot twice

From: Xiaofei Tan <[email protected]>

[ Upstream commit 6ba0fbc35aa9f3bc8c12be3b4047055c9ce2ac92 ]

The function hisi_sas_slot_task_free() is used to free the slot and do tidy-up of LLDD resources. The LLDD generally should know the state of a slot and decide when to free it, and it should only be done once.

For some scenarios, we really don't know the state, like when TMF timeout. In this case, we check task->lldd_task before calling hisi_sas_slot_task_free().

However, we may miss some scenarios when we should also check task->lldd_task, and it is not SMP safe to check task->lldd_task as we don't protect it within spin lock.

This patch is to fix this risk of freeing slot twice, as follows:

1. Check task->lldd_task in the hisi_sas_slot_task_free(), and give

     up freeing of this time if task->lldd_task is NULL.

2. Set slot->buf to NULL after it is freed.

---
 drivers/scsi/hisi_sas/hisi_sas_main.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

@@ -185,13 +185,16 @@ void hisi_sas_slot_task_free(struct hisi
 		struct domain_device *device = task->dev;
 		struct hisi_sas_device *sas_dev = device->lldd_dev;
 
+		if (!task->lldd_task)
+			return;
+
+		task->lldd_task = NULL;
+
 		if (!sas_protocol_ata(task->task_proto))
 			if (slot->n_elem)
 				dma_unmap_sg(dev, task->scatter, slot->n_elem,
 					     task->data_dir);
 
-		task->lldd_task = NULL;
-
 		if (sas_dev)
 			atomic64_dec(&sas_dev->running_req);
 	}

@@ -199,8 +202,8 @@ void hisi_sas_slot_task_free(struct hisi
 	if (slot->buf)
 		dma_pool_free(hisi_hba->buffer_pool, slot->buf, slot->buf_dma);
 
-
 	list_del_init(&slot->entry);
+	slot->buf = NULL;
 	slot->task = NULL;
 	slot->port = NULL;
 	hisi_sas_slot_index_free(hisi_hba, slot->idx);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/scsi-hisi_sas-fix-the-risk-of-freeing-slot-twice.patch