[PATCH v3 2/2] scsi: leapraid: serialize firmware log mmap with teardown

leapraid_fw_log_exit() waits for mmap_refcnt to reach zero before it
frees the firmware log buffer.  leapraid_fw_mmap() checks
host_removing, but it does not increment mmap_refcnt until after
dma_mmap_coherent() succeeds and the VMA open callback runs.

Removal can set host_removing and observe a zero mmap_refcnt between
the check and the VMA open.  It can then free the coherent buffer while
the mmap path is still establishing a userspace mapping of it.

Claim a temporary mmap reference while looking up the adapter under
leapraid_adapter_lock.  Removal deletes the adapter from the same
locked list after setting host_removing, so a mapping is either
rejected or included in the count that removal waits for.  Drop the
temporary reference on the common exit path, after a successful VMA
open has acquired the reference covering the VMA lifetime.

Fixes: 5597088c9e79 ("scsi: leapraid: Add new SCSI driver")
Signed-off-by: Linmao Li <[email protected]>
---
 drivers/scsi/leapraid/leapraid_app.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/leapraid/leapraid_app.c b/drivers/scsi/leapraid/leapraid_app.c
index 841027ce2501c..84eef50947aea 100644
--- a/drivers/scsi/leapraid/leapraid_app.c
+++ b/drivers/scsi/leapraid/leapraid_app.c
@@ -171,7 +171,8 @@ static int leapraid_ctl_validate_sge_offset(struct leapraid_adapter *adapter,
 	return 0;
 }
 
-static struct leapraid_adapter *leapraid_ctl_lookup_adapter(int adapter_id)
+static struct leapraid_adapter *leapraid_ctl_lookup_adapter(int adapter_id,
+							    bool track_mmap)
 {
 	struct leapraid_adapter *adapter;
 	struct Scsi_Host *shost;
@@ -184,6 +185,8 @@ static struct leapraid_adapter *leapraid_ctl_lookup_adapter(int adapter_id)
 			shost = adapter->shost;
 			if (!shost || !scsi_host_get(shost))
 				break;
+			if (track_mmap)
+				atomic_inc(&adapter->fw_log_desc.mmap_refcnt);
 			spin_unlock(&leapraid_adapter_lock);
 			return adapter;
 		}
@@ -589,7 +592,7 @@ static int leapraid_ctl_ioctl_main(struct file *file, unsigned int cmd,
 		return -EFAULT;
 	}
 
-	adapter = leapraid_ctl_lookup_adapter(ioctl_header.adapter_id);
+	adapter = leapraid_ctl_lookup_adapter(ioctl_header.adapter_id, false);
 	if (!adapter)
 		return -EFAULT;
 
@@ -728,7 +731,7 @@ static int leapraid_fw_mmap(struct file *filp, struct vm_area_struct *vma)
 
 	length = vma->vm_end - vma->vm_start;
 
-	adapter = leapraid_ctl_lookup_adapter(adapter_id);
+	adapter = leapraid_ctl_lookup_adapter(adapter_id, true);
 	if (!adapter) {
 		pr_err("%s: No adapter found!\n", __func__);
 		return -EINVAL;
@@ -771,6 +774,9 @@ static int leapraid_fw_mmap(struct file *filp, struct vm_area_struct *vma)
 
 	rc = 0;
 out_put:
+	if (adapter &&
+	    atomic_dec_and_test(&adapter->fw_log_desc.mmap_refcnt))
+		wake_up(&adapter->fw_log_desc.mmap_waitq);
 	leapraid_ctl_put_adapter(adapter);
 	return rc;
 }
-- 
2.25.1