linux-kernel - [PATCH 7/9] habanalabs: protect only pointer dereference in hard-reset

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Date:   Sun, 28 Jul 2019 14:28:16 +0300
From:   Oded Gabbay <oded.gabbay@...il.com>
To:     linux-kernel@...r.kernel.org, oshpigelman@...ana.ai,
        ttayar@...ana.ai, gregkh@...uxfoundation.org
Subject: [PATCH 7/9] habanalabs: protect only pointer dereference in hard-reset

This patch changes the location of taking a mutex lock and releasing it
during the hard-reset process of the ASIC.

The only place we need to protect is when we dereference pointers that may
go away in case the user process aborts/closes the FD.

That way, we allow the user process to actually close its FD in case we
tell him that an error occurred.

Signed-off-by: Oded Gabbay <oded.gabbay@...il.com>
---
 drivers/misc/habanalabs/device.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/misc/habanalabs/device.c b/drivers/misc/habanalabs/device.c
index 5400e65ba5fa..471506b54217 100644
--- a/drivers/misc/habanalabs/device.c
+++ b/drivers/misc/habanalabs/device.c
@@ -574,20 +574,21 @@ static void device_kill_open_processes(struct hl_device *hdev)
 	else
 		pending_total = HL_PENDING_RESET_PER_SEC;
 
-	pending_cnt = pending_total;
-
 	/* Flush all processes that are inside hl_open */
 	mutex_lock(&hdev->fpriv_list_lock);
+	mutex_unlock(&hdev->fpriv_list_lock);
 
-	while ((!list_empty(&hdev->fpriv_list)) && (pending_cnt)) {
-
-		pending_cnt--;
-
-		dev_info(hdev->dev,
-			"Can't HARD reset, waiting for user to close FD\n");
+	/* Giving time for user to close FD, and for processes that are inside
+	 * hl_device_open to finish
+	 */
+	if (!list_empty(&hdev->fpriv_list))
 		ssleep(1);
-	}
 
+	mutex_lock(&hdev->fpriv_list_lock);
+
+	/* This section must be protected because we are dereferencing
+	 * pointers that are freed if the process exits
+	 */
 	if (!list_empty(&hdev->fpriv_list)) {
 		task = get_pid_task(hdev->compute_ctx->hpriv->taskpid,
 					PIDTYPE_PID);
@@ -600,6 +601,8 @@ static void device_kill_open_processes(struct hl_device *hdev)
 		}
 	}
 
+	mutex_unlock(&hdev->fpriv_list_lock);
+
 	/* We killed the open users, but because the driver cleans up after the
 	 * user contexts are closed (e.g. mmu mappings), we need to wait again
 	 * to make sure the cleaning phase is finished before continuing with
@@ -609,6 +612,8 @@ static void device_kill_open_processes(struct hl_device *hdev)
 	pending_cnt = pending_total;
 
 	while ((!list_empty(&hdev->fpriv_list)) && (pending_cnt)) {
+		dev_info(hdev->dev,
+			"Waiting for all unmap operations to finish before hard reset\n");
 
 		pending_cnt--;
 
@@ -618,9 +623,6 @@ static void device_kill_open_processes(struct hl_device *hdev)
 	if (!list_empty(&hdev->fpriv_list))
 		dev_crit(hdev->dev,
 			"Going to hard reset with open user contexts\n");
-
-	mutex_unlock(&hdev->fpriv_list_lock);
-
 }
 
 static void device_hard_reset_pending(struct work_struct *work)
-- 
2.17.1