[PATCH 1/8] misc: fastrpc: Avoid free of DMA buffer in interrupt context

[Srinivas Kandagatla]

From: Thierry Escande <thierry.esca...@linaro.org>

When the remote DSP invocation is interrupted by the user, the
associated DMA buffer can be freed in interrupt context causing a kernel
BUG.

This patch adds a worker thread associated to the fastrpc context. It
is scheduled in the rpmsg callback to decrease its refcount out of the
interrupt context.

Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
Signed-off-by: Thierry Escande <thierry.esca...@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandaga...@linaro.org>
---
 drivers/misc/fastrpc.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 89aec17738ef..82e7217ae87a 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -149,6 +149,7 @@ struct fastrpc_invoke_ctx {
        struct kref refcount;
        struct list_head node; /* list of ctxs */
        struct completion work;
+       struct work_struct put_work;
        struct fastrpc_msg msg;
        struct fastrpc_user *fl;
        struct fastrpc_remote_arg *rpra;
@@ -311,6 +312,14 @@ static void fastrpc_context_put(struct fastrpc_invoke_ctx 
*ctx)
        kref_put(&ctx->refcount, fastrpc_context_free);
 }
 
+static void fastrpc_context_put_wq(struct work_struct *work)
+{
+       struct fastrpc_invoke_ctx *ctx =
+                       container_of(work, struct fastrpc_invoke_ctx, put_work);
+
+       fastrpc_context_put(ctx);
+}
+
 static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
                        struct fastrpc_user *user, u32 kernel, u32 sc,
                        struct fastrpc_invoke_args *args)
@@ -345,6 +354,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
        ctx->tgid = user->tgid;
        ctx->cctx = cctx;
        init_completion(&ctx->work);
+       INIT_WORK(&ctx->put_work, fastrpc_context_put_wq);
 
        spin_lock(&user->lock);
        list_add_tail(&ctx->node, &user->pending);
@@ -1349,7 +1359,13 @@ static int fastrpc_rpmsg_callback(struct rpmsg_device 
*rpdev, void *data,
 
        ctx->retval = rsp->retval;
        complete(&ctx->work);
-       fastrpc_context_put(ctx);
+
+       /*
+        * The DMA buffer associated with the context cannot be freed in
+        * interrupt context so schedule it through a worker thread to
+        * avoid a kernel BUG.
+        */
+       schedule_work(&ctx->put_work);
 
        return 0;
 }
-- 
2.21.0