[PATCH char-misc] mei: pull kvfree out of spinlock

[Alexander Usyskin]

The read buffer allocation was changed from kmalloc() to kvmalloc().

This buffer is part of mei_cl_cb structure that can be queued in
rd_complete queue protected by spinlock.
Releasing the structure leads to errors like below when freeing buffer
that allocated non-contiguous:

BUG: sleeping function called from invalid context at mm/vmalloc.c:3448

Separate mei_cl_cb structure dequeue and release to
perform only dequeue under spinlock and push release out of spinlock.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 4adf613e01bf ("mei: use kvmalloc for read buffer")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16359
Reviewed-by: Menachem Adin <menachem.adin@xxxxxxxxx>
Signed-off-by: Alexander Usyskin <alexander.usyskin@xxxxxxxxx>
---
 drivers/misc/mei/client.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/misc/mei/client.c b/drivers/misc/mei/client.c
index 643b0039cc72..26d2b2742d50 100644
--- a/drivers/misc/mei/client.c
+++ b/drivers/misc/mei/client.c
@@ -425,18 +425,24 @@ static void mei_io_tx_list_free_cl(struct list_head *head,
 }
 
 /**
- * mei_io_list_free_fp - free cb from a list that matches file pointer
+ * mei_io_rd_list_free_fp - free cb from a rd_completed list that matches file pointer
  *
- * @head: io list
+ * @cl: host client
  * @fp: file pointer (matching cb file object), may be NULL
  */
-static void mei_io_list_free_fp(struct list_head *head, const struct file *fp)
+static void mei_io_rd_list_free_fp(struct mei_cl *cl, const struct file *fp)
 {
 	struct mei_cl_cb *cb, *next;
+	LIST_HEAD(cmpl_list);
 
-	list_for_each_entry_safe(cb, next, head, list)
+	spin_lock(&cl->rd_completed_lock);
+	list_for_each_entry_safe(cb, next, &cl->rd_completed, list)
 		if (!fp || fp == cb->fp)
-			mei_io_cb_free(cb);
+			list_move(&cb->list, &cmpl_list);
+	spin_unlock(&cl->rd_completed_lock);
+
+	list_for_each_entry_safe(cb, next, &cmpl_list, list)
+		mei_io_cb_free(cb);
 }
 
 /**
@@ -565,9 +571,7 @@ int mei_cl_flush_queues(struct mei_cl *cl, const struct file *fp)
 		mei_io_list_flush_cl(&cl->dev->ctrl_rd_list, cl);
 		mei_cl_free_pending(cl);
 	}
-	spin_lock(&cl->rd_completed_lock);
-	mei_io_list_free_fp(&cl->rd_completed, fp);
-	spin_unlock(&cl->rd_completed_lock);
+	mei_io_rd_list_free_fp(cl, fp);
 
 	return 0;
 }
@@ -1401,7 +1405,7 @@ void mei_cl_add_rd_completed(struct mei_cl *cl, struct mei_cl_cb *cb)
 }
 
 /**
- * mei_cl_del_rd_completed - free read completed callback with lock
+ * mei_cl_del_rd_completed - unlink read completed callback with lock and free it
  *
  * @cl: host client
  * @cb: callback block
@@ -1410,8 +1414,9 @@ void mei_cl_add_rd_completed(struct mei_cl *cl, struct mei_cl_cb *cb)
 void mei_cl_del_rd_completed(struct mei_cl *cl, struct mei_cl_cb *cb)
 {
 	spin_lock(&cl->rd_completed_lock);
-	mei_io_cb_free(cb);
+	list_del_init(&cb->list);
 	spin_unlock(&cl->rd_completed_lock);
+	mei_io_cb_free(cb);
 }
 
 /**

---
base-commit: 775553d19b163446c38c5ff24dd0a01065376932
change-id: 20260719-kvfree_out_of_spinlock-fbc1acdd6a66

Best regards,
-- 
Alexander Usyskin <alexander.usyskin@xxxxxxxxx>