[PATCH v2] misc: fastrpc: fix context leak and hang on signal-interrupted invoke

[Anandu Krishnan E <anandu.e@oss.qualcomm.com>]

fastrpc invokes work by sending an RPC message to the DSP and blocking
in wait_for_completion_interruptible() until the DSP responds. If a
signal arrives during this wait, the syscall returns -ERESTARTSYS and
the invoke context which holds the in-flight DMA buffers and
completion state is left stranded in fl->pending.

On the next syscall attempt (either auto-restarted by the kernel via
SA_RESTART or manually retried by user-space after EINTR), a fresh
context is allocated and the RPC message is re-sent to the DSP. This
has two consequences:

  - The original context leaks in fl->pending until the file is closed.
  - The DSP receives a duplicate invocation. If the DSP was mid-way
    through processing the first request and had issued a reverse RPC
    call back to the host, the retry sends a new forward request
    instead of the expected reverse-RPC response. The DSP thread
    waiting for that response is never woken, causing a hang.

Fix this by saving the interrupted context to a new fl->interrupted
list on -ERESTARTSYS. When the same thread retries the invoke with a
matching sc, restore the context and jump directly to the wait,
skipping context allocation and message re-send.

Three additional bugs are also fixed:

1. fastrpc_context_save_interrupted() did not drop the extra kref that
   fastrpc_invoke_send() took, so the worker's put only reached 1 and
   the context was never freed.  Drop the reference in save_interrupted()
   so the worker's put reaches 0 and triggers context_free.

2. The bail path skipped context cleanup on -ETIMEDOUT, leaking the
   context.  Remove the -ETIMEDOUT exception so timed-out contexts are
   freed like any other error path.

3. fastrpc_context_free() did not remove the context from fl->interrupted
   before freeing it.  A context freed via a racing channel removal left
   a dangling node in the list.  Add list_del_init() guarded by fl->lock
   before releasing resources.

Also drain fl->interrupted on process exit, complete any sleeping
contexts with -EPIPE and schedule put_wq to drop the worker ref when
the rpmsg channel is removed, and add dev_warn() on TIMEOUT and
ERESTARTSYS to aid post-mortem debugging.

Remove the obsolete invoke_interrupted_mmaps mechanism from
fastrpc_channel_ctx; context resources are now kept alive through the
context refcount rather than by migrating mmaps to a channel-level list.

Fixes: 387f625585d1 ("misc: fastrpc: handle interrupted contexts")
Cc: stable@kernel.org
Co-developed-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
Signed-off-by: Anandu Krishnan E <anandu.e@oss.qualcomm.com>
---
This patch fixes a context leak and DSP hang that occur when a
fastrpc invoke syscall is interrupted by a signal, along with three
follow-on bugs found during review.

Changes in v2:
- Fix kref imbalance: fastrpc_context_save_interrupted() now drops the
  extra reference taken by fastrpc_invoke_send(), so the worker's put
  correctly reaches 0 and triggers context_free.
- Fix -ETIMEDOUT context leak: remove the ETIMEDOUT exception from the
  bail path so timed-out kernel invocations go through the same
  list_del_init + context_put cleanup as all other error paths.
- Fix dangling node: fastrpc_context_free() now calls list_del_init()
  under fl->lock before releasing resources, preventing a dangling node
  in fl->interrupted if a racing channel removal fires put_wq.
- fastrpc_notify_users() now calls schedule_work(&ctx->put_work) for
  interrupted contexts to drop the worker ref on channel removal.
- Add dev_warn() on TIMEOUT and ERESTARTSYS for post-mortem debugging.
- Use list_del_init() instead of list_del() in the bail path.

Link to v1: https://lore.kernel.org/all/20260525124222.3082420-1-anandu.e@oss.qualcomm.com/
---
 drivers/misc/fastrpc.c | 101 +++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 82 insertions(+), 19 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index f3a49384586d..c0859a501617 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -280,7 +280,6 @@ struct fastrpc_channel_ctx {
 	struct fastrpc_device *secure_fdevice;
 	struct fastrpc_device *fdevice;
 	struct fastrpc_buf *remote_heap;
-	struct list_head invoke_interrupted_mmaps;
 	bool secure;
 	bool unsigned_support;
 	u64 dma_mask;
@@ -297,6 +296,7 @@ struct fastrpc_user {
 	struct list_head user;
 	struct list_head maps;
 	struct list_head pending;
+	struct list_head interrupted;
 	struct list_head mmaps;
 
 	struct fastrpc_channel_ctx *cctx;
@@ -522,6 +522,11 @@ static void fastrpc_user_free(struct kref *ref)
 		fastrpc_context_put(ctx);
 	}
 
+	list_for_each_entry_safe(ctx, n, &fl->interrupted, node) {
+		list_del(&ctx->node);
+		fastrpc_context_put(ctx);
+	}
+
 	list_for_each_entry_safe(map, m, &fl->maps, node)
 		fastrpc_map_put(map);
 
@@ -557,6 +562,12 @@ static void fastrpc_context_free(struct kref *ref)
 	cctx = ctx->cctx;
 	fl = ctx->fl;
 
+	/* Remove from fl->interrupted if present; no-op for normal paths. */
+	spin_lock(&fl->lock);
+	if (!list_empty(&ctx->node))
+		list_del_init(&ctx->node);
+	spin_unlock(&fl->lock);
+
 	for (i = 0; i < ctx->nbufs; i++)
 		fastrpc_map_put(ctx->maps[i]);
 
@@ -594,6 +605,42 @@ static void fastrpc_context_put_wq(struct work_struct *work)
 	fastrpc_context_put(ctx);
 }
 
+static void fastrpc_context_save_interrupted(struct fastrpc_invoke_ctx *ctx)
+{
+	spin_lock(&ctx->fl->lock);
+	list_del(&ctx->node);
+	list_add_tail(&ctx->node, &ctx->fl->interrupted);
+	spin_unlock(&ctx->fl->lock);
+	/*
+	 * invoke_send bumped the kref to 2; the bail path skips the put
+	 * for ERESTARTSYS.  Drop it here so the worker's put reaches 0
+	 * and triggers context_free.
+	 */
+	fastrpc_context_put(ctx);
+}
+
+static struct fastrpc_invoke_ctx *fastrpc_context_restore_interrupted(
+			struct fastrpc_user *fl, u32 sc)
+{
+	struct fastrpc_invoke_ctx *ctx = NULL, *ictx, *n;
+
+	spin_lock(&fl->lock);
+	list_for_each_entry_safe(ictx, n, &fl->interrupted, node) {
+		if (ictx->pid != current->pid)
+			continue;
+		if (ictx->sc != sc || ictx->fl != fl) {
+			spin_unlock(&fl->lock);
+			return ERR_PTR(-EINVAL);
+		}
+		ctx = ictx;
+		list_del(&ctx->node);
+		list_add_tail(&ctx->node, &fl->pending);
+		break;
+	}
+	spin_unlock(&fl->lock);
+	return ctx;
+}
+
 #define CMP(aa, bb) ((aa) == (bb) ? 0 : (aa) < (bb) ? -1 : 1)
 static int olaps_cmp(const void *a, const void *b)
 {
@@ -1243,8 +1290,6 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
 				   struct fastrpc_invoke_args *args)
 {
 	struct fastrpc_invoke_ctx *ctx = NULL;
-	struct fastrpc_buf *buf, *b;
-
 	int err = 0;
 
 	if (!fl->sctx)
@@ -1258,6 +1303,14 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
 		return -EPERM;
 	}
 
+	if (!kernel) {
+		ctx = fastrpc_context_restore_interrupted(fl, sc);
+		if (IS_ERR(ctx))
+			return PTR_ERR(ctx);
+		if (ctx)
+			goto wait;
+	}
+
 	ctx = fastrpc_context_alloc(fl, kernel, sc, args);
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
@@ -1273,11 +1326,20 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
 	if (err)
 		goto bail;
 
+wait:
 	if (kernel) {
-		if (!wait_for_completion_timeout(&ctx->work, 10 * HZ))
+		if (!wait_for_completion_timeout(&ctx->work, 10 * HZ)) {
 			err = -ETIMEDOUT;
+			dev_warn(fl->sctx->dev,
+				"fastrpc_invoke: TIMEOUT ctxid=0x%llx handle=0x%x nscalars=%d\n",
+				ctx->ctxid, handle, ctx->nscalars);
+		}
 	} else {
 		err = wait_for_completion_interruptible(&ctx->work);
+		if (err == -ERESTARTSYS)
+			dev_warn(fl->sctx->dev,
+				"fastrpc_invoke: INTERRUPTED ctxid=0x%llx handle=0x%x nscalars=%d\n",
+				ctx->ctxid, handle, ctx->nscalars);
 	}
 
 	if (err)
@@ -1296,21 +1358,15 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
 		goto bail;
 
 bail:
-	if (err != -ERESTARTSYS && err != -ETIMEDOUT) {
-		/* We are done with this compute context */
+	if (ctx && err == -ERESTARTSYS) {
+		fastrpc_context_save_interrupted(ctx);
+	} else if (ctx) {
 		spin_lock(&fl->lock);
-		list_del(&ctx->node);
+		list_del_init(&ctx->node);
 		spin_unlock(&fl->lock);
 		fastrpc_context_put(ctx);
 	}
 
-	if (err == -ERESTARTSYS) {
-		list_for_each_entry_safe(buf, b, &fl->mmaps, node) {
-			list_del(&buf->node);
-			list_add_tail(&buf->node, &fl->cctx->invoke_interrupted_mmaps);
-		}
-	}
-
 	if (err)
 		dev_dbg(fl->sctx->dev, "Error: Invoke Failed %d\n", err);
 
@@ -1662,6 +1718,7 @@ static int fastrpc_device_open(struct inode *inode, struct file *filp)
 	spin_lock_init(&fl->lock);
 	mutex_init(&fl->mutex);
 	INIT_LIST_HEAD(&fl->pending);
+	INIT_LIST_HEAD(&fl->interrupted);
 	INIT_LIST_HEAD(&fl->maps);
 	INIT_LIST_HEAD(&fl->mmaps);
 	INIT_LIST_HEAD(&fl->user);
@@ -2460,7 +2517,6 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 	rdev->dma_mask = &data->dma_mask;
 	dma_set_mask_and_coherent(rdev, DMA_BIT_MASK(32));
 	INIT_LIST_HEAD(&data->users);
-	INIT_LIST_HEAD(&data->invoke_interrupted_mmaps);
 	spin_lock_init(&data->lock);
 	idr_init(&data->ctx_idr);
 	data->domain_id = domain_id;
@@ -2493,13 +2549,23 @@ static void fastrpc_notify_users(struct fastrpc_user *user)
 		ctx->retval = -EPIPE;
 		complete(&ctx->work);
 	}
+	/*
+	 * Interrupted contexts hold two refs: one for the invoker and one
+	 * for the async worker from fastrpc_invoke_send.  Complete them so
+	 * any blocked retry wakes, and schedule put_wq to drop the worker
+	 * ref -- the invoker ref is released by fastrpc_user_free().
+	 */
+	list_for_each_entry(ctx, &user->interrupted, node) {
+		ctx->retval = -EPIPE;
+		complete(&ctx->work);
+		schedule_work(&ctx->put_work);
+	}
 	spin_unlock(&user->lock);
 }
 
 static void fastrpc_rpmsg_remove(struct rpmsg_device *rpdev)
 {
 	struct fastrpc_channel_ctx *cctx = dev_get_drvdata(&rpdev->dev);
-	struct fastrpc_buf *buf, *b;
 	struct fastrpc_user *user;
 	unsigned long flags;
 
@@ -2516,9 +2582,6 @@ static void fastrpc_rpmsg_remove(struct rpmsg_device *rpdev)
 	if (cctx->secure_fdevice)
 		misc_deregister(&cctx->secure_fdevice->miscdev);
 
-	list_for_each_entry_safe(buf, b, &cctx->invoke_interrupted_mmaps, node)
-		list_del(&buf->node);
-
 	if (cctx->remote_heap)
 		fastrpc_buf_free(cctx->remote_heap);
 

---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260701-master-2ba6246f29d1

Best regards,
--  
Anandu Krishnan E <anandu.e@oss.qualcomm.com>