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

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

On 24-07-2026 04:50 pm, Srinivas Kandagatla wrote:
>
> On 7/1/26 9:11 AM, Anandu Krishnan E wrote:
>> 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>
>> ---
> Does not apply to linux-next.
>
> Can you rebase and resend.
sure will share 
-- anandu 
>
> --srini
>
>> 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>
>>