Re: [PATCH v3] misc: fastrpc: fix context leak and hang on signal-interrupted invoke

[Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>]

On 02-10-2026 01:15, 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, instead of freeing it or leaving it on
> fl->pending. The context keeps the same reference it already held;
> only list membership changes, so the refcount stays symmetric no
> matter how many times a context is interrupted and retried. When the
> same thread retries the invoke with a matching handle and sc, the
> context is pulled back onto fl->pending and the call jumps straight
> to the wait, skipping context allocation and message re-send. Any
> retry whose handle/sc does not match a parked context simply falls
> through to a normal fresh allocation, so a thread that goes on to
> issue a different call after an interrupted one is never wedged.
> ctx->args is repointed at the retry's own args on resume so DSP output
> lands in the current call's buffers rather than the original,
> already-freed ones; fastrpc_context_alloc() now also takes its own
> copy of args up front, so ctx->args is always owned by the context and
> is freed exactly once, by fastrpc_context_free(), regardless of
> whether the context completes normally, is resumed after an
> interruption, or is drained unresumed.
> 
> A context parked on fl->interrupted is reachable from three places
> that can run concurrently: a resumed retry, process exit, and SSR via
> rpmsg channel removal/notify. fastrpc_context_free() now removes the
> context from whichever list it is on before releasing its resources,
> using list_del_init() (plain list_del() poisons the node, which would
> otherwise break this same check if the context is freed via a race
> with one of the exit/SSR drains). fastrpc_device_release() and
> fastrpc_rpmsg_remove()'s fastrpc_notify_users() both drain
> fl->interrupted, completing any parked context with -EPIPE and
> dropping the invoker's reference, so a context stuck there at fd close
> or channel teardown cannot leak the context -- or, in the fd-close
> case, fl itself, since fl's own reference is held via the context
> until this drain releases it. Because the DSP response worker
> (fastrpc_rpmsg_callback()) and the exit/SSR path can both end up
> scheduling the same ctx->put_work for a parked context, a
> put_work_scheduled flag checked and set under fl->lock ensures only
> one of them actually queues it.
> 
> The -ETIMEDOUT path is also brought in line with normal cleanup: it
> used to be exempted from the bail-path list_del()/context_put(),
> leaking the context on every kernel-invocation timeout.
> 
> 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 seven
> follow-on bugs found during review and self-review.
> 
> Changes in v3:
> - fastrpc_context_save_interrupted() no longer drops a reference when
>   parking the context, fixing a kref double-put that left the context
>   under-refcounted.
> - Restoring an interrupted context now matches on both handle and sc,
>   not sc alone, so a stale/differently-shaped retry cannot be handed a
>   buffer layout it didn't allocate.
> - A mismatched handle/sc on retry now falls through to allocating a
>   fresh context instead of returning -EINVAL, so a thread issuing a
>   different call after an interrupted one is never permanently
>   wedged.
> - Added a put_work_scheduled flag, checked and set under fl->lock, to
>   guard against fastrpc_notify_users() and fastrpc_rpmsg_callback()
>   both scheduling put_work for the same context.
> - fastrpc_device_release() now drains fl->interrupted and drops the
>   invoker's reference on each parked context before releasing its own
>   reference on fl, fixing a leak of both fl and the context if the fd
>   is closed while a context is still parked.
> - fastrpc_device_release()'s and fastrpc_user_free()'s drain loops now
>   use list_del_init() instead of list_del(), avoiding a poisoned-node
>   list_empty() check in fastrpc_context_free().
> - fastrpc_invoke_send() can return -ERESTARTSYS from rpmsg_send()
>   itself before the message is ever delivered to the DSP. This is now
>   distinguished with a `sent` flag so only a completion-wait
>   interruption after a successful send is parked as resumable.
> - ctx->args is now repointed at the retry's args on resume instead of
>   pointing at the original call's already-freed buffers; an
>   args_owned flag lets fastrpc_context_free() free ctx->args if a
>   parked context is drained/abandoned without ever being resumed.
> 
> Link to v2: https://lore.kernel.org/all/805d5de8-477c-41e9-b192-d889d1cca9b6@oss.qualcomm.com/
> Link to v1: https://lore.kernel.org/all/20260525124222.3082420-1-anandu.e@oss.qualcomm.com/
> ---
>  drivers/misc/fastrpc.c | 157 ++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 129 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 5ac7b3e78ba7..f51cb772e683 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -261,6 +261,7 @@ struct fastrpc_invoke_ctx {
>  	int pid;
>  	int client_id;
>  	u32 sc;
> +	u32 handle;
>  	u64 *fdlist;
>  	u32 *crc;
>  	/* Poll memory that DSP updates */
> @@ -271,6 +272,8 @@ struct fastrpc_invoke_ctx {
>  	bool is_work_done;
>  	/* process updates poll memory instead of glink response */
>  	bool is_polled;
> +	/* set once put_work has been scheduled for this ctx, guarded by fl->lock */
> +	bool put_work_scheduled;
>  	struct kref refcount;
>  	struct list_head node; /* list of ctxs */
>  	struct completion work;
> @@ -320,7 +323,6 @@ struct fastrpc_channel_ctx {
>  	u32 dsp_attributes[FASTRPC_MAX_DSP_ATTRIBUTES];
>  	struct fastrpc_device *secure_fdevice;
>  	struct fastrpc_device *fdevice;
> -	struct list_head invoke_interrupted_mmaps;
>  	bool secure;
>  	bool unsigned_support;
>  	bool poll_mode_supported;
> @@ -340,6 +342,7 @@ 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;
> @@ -566,7 +569,12 @@ static void fastrpc_user_free(struct kref *ref)
>  	fastrpc_buf_free(fl->init_mem);
>  
>  	list_for_each_entry_safe(ctx, n, &fl->pending, node) {
> -		list_del(&ctx->node);
> +		list_del_init(&ctx->node);
> +		fastrpc_context_put(ctx);
this looks unrelated

> +	}
> +
> +	list_for_each_entry_safe(ctx, n, &fl->interrupted, node) {
> +		list_del_init(&ctx->node);
>  		fastrpc_context_put(ctx);
>  	}
>  
> @@ -605,6 +613,11 @@ static void fastrpc_context_free(struct kref *ref)
>  	cctx = ctx->cctx;
>  	fl = ctx->fl;
>  
> +	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]);
>  
> @@ -616,6 +629,7 @@ static void fastrpc_context_free(struct kref *ref)
>  
>  	kfree(ctx->maps);
>  	kfree(ctx->olaps);
> +	kfree(ctx->args);
>  	kfree(ctx);
>  
>  	/* Release the reference taken in fastrpc_context_alloc() */
> @@ -641,6 +655,50 @@ static void fastrpc_context_put_wq(struct work_struct *work)
>  	fastrpc_context_put(ctx);
>  }
>  
> +/* Ensures put_work is scheduled at most once per ctx; racing callers may both try. */
> +static void fastrpc_context_schedule_put_work(struct fastrpc_invoke_ctx *ctx)
> +{
> +	bool do_schedule;
> +
> +	spin_lock(&ctx->fl->lock);
> +	do_schedule = !ctx->put_work_scheduled;
> +	ctx->put_work_scheduled = true;
> +	spin_unlock(&ctx->fl->lock);
> +
> +	if (do_schedule)
> +		schedule_work(&ctx->put_work);
> +}
> +
> +/* References taken for ctx are left intact; ownership just moves between lists. */
> +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);
> +}
> +
> +/* Matches on handle+sc, not sc alone, to avoid resuming an unrelated call. */
> +static struct fastrpc_invoke_ctx *fastrpc_context_restore_interrupted(
> +			struct fastrpc_user *fl, u32 handle, u32 sc)
> +{
> +	struct fastrpc_invoke_ctx *ctx = NULL, *ictx;
> +
> +	spin_lock(&fl->lock);
> +	list_for_each_entry(ictx, &fl->interrupted, node) {
> +		if (ictx->pid == current->pid && ictx->handle == handle &&
> +		    ictx->sc == sc) {
> +			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)
>  {
> @@ -721,7 +779,15 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
>  			kfree(ctx);
>  			return ERR_PTR(-ENOMEM);
>  		}
> -		ctx->args = args;
> +		/* Own copy: ctx may outlive the caller's args if parked on fl->interrupted. */
> +		ctx->args = kzalloc_objs(*ctx->args, ctx->nscalars);
> +		if (!ctx->args) {
> +			kfree(ctx->olaps);
> +			kfree(ctx->maps);
> +			kfree(ctx);
> +			return ERR_PTR(-ENOMEM);
> +		}
> +		memcpy(ctx->args, args, ctx->nscalars * sizeof(*args));
>  		fastrpc_get_buff_overlaps(ctx);
>  	}
>  
> @@ -765,6 +831,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
>  	fastrpc_channel_ctx_put(cctx);
>  	kfree(ctx->maps);
>  	kfree(ctx->olaps);
> +	kfree(ctx->args);
>  	kfree(ctx);
>  
>  	return ERR_PTR(ret);
> @@ -1325,10 +1392,18 @@ static inline int fastrpc_wait_for_response(struct fastrpc_invoke_ctx *ctx,
>  	int err = 0;
>  
>  	if (kernel) {
> -		if (!wait_for_completion_timeout(&ctx->work, 10 * HZ))
> +		if (!wait_for_completion_timeout(&ctx->work, 10 * HZ)) {
>  			err = -ETIMEDOUT;
> +			dev_warn(ctx->fl->sctx->dev,
> +				 "fastrpc_invoke: TIMEOUT ctxid=0x%llx handle=0x%x nscalars=%d\n",
> +				 ctx->ctxid, ctx->handle, ctx->nscalars);
> +		}
>  	} else {
>  		err = wait_for_completion_interruptible(&ctx->work);
> +		if (err == -ERESTARTSYS)
> +			dev_warn(ctx->fl->sctx->dev,
> +				 "fastrpc_invoke: INTERRUPTED ctxid=0x%llx handle=0x%x nscalars=%d\n",
> +				 ctx->ctxid, ctx->handle, ctx->nscalars);
should the logs be at debug/rate-limited level?

>  	}
>  
>  	return err;
> @@ -1355,8 +1430,7 @@ 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;
> -
> +	bool resumed = false;
>  	int err = 0;
>  
>  	if (!fl->sctx)
> @@ -1370,9 +1444,21 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
>  		return -EPERM;
>  	}
>  
> -	ctx = fastrpc_context_alloc(fl, kernel, sc, args);
> -	if (IS_ERR(ctx))
> -		return PTR_ERR(ctx);
> +	if (!kernel)
> +		ctx = fastrpc_context_restore_interrupted(fl, handle, sc);
> +
> +	if (ctx) {
> +		/* ctx->args is already populated from before the interruption. */
> +		resumed = true;
goto wait;

> +	} else {
> +		ctx = fastrpc_context_alloc(fl, kernel, sc, args);
> +		if (IS_ERR(ctx))
> +			return PTR_ERR(ctx);
> +		ctx->handle = handle;
> +	}
> +
> +	if (resumed)
> +		goto wait;
>  
>  	err = fastrpc_get_args(kernel, ctx);
>  	if (err)
> @@ -1392,6 +1478,7 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
>  	if (handle > FASTRPC_MAX_STATIC_HANDLE && fl->pd == USER_PD && fl->poll_mode)
>  		ctx->is_polled = true;
>  
> +wait:
>  	err = fastrpc_wait_for_completion(ctx, kernel);
>  	if (err)
>  		goto bail;
> @@ -1409,21 +1496,13 @@ 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 */
> -		spin_lock(&fl->lock);
> -		list_del(&ctx->node);
> -		spin_unlock(&fl->lock);
> -		fastrpc_context_put(ctx);
> -	}
> -
>  	if (err == -ERESTARTSYS) {
> +		fastrpc_context_save_interrupted(ctx);
> +	} else {
>  		spin_lock(&fl->lock);
> -		list_for_each_entry_safe(buf, b, &fl->mmaps, node) {
> -			list_del(&buf->node);
> -			list_add_tail(&buf->node, &fl->cctx->invoke_interrupted_mmaps);
> -		}
> +		list_del_init(&ctx->node);
fastrpc_context_free will also remove from list, what is the reason to
have it in 2 places?

>  		spin_unlock(&fl->lock);
> +		fastrpc_context_put(ctx);
>  	}
>  
>  	if (err)
> @@ -1725,6 +1804,7 @@ static int fastrpc_device_release(struct inode *inode, struct file *file)
>  {
>  	struct fastrpc_user *fl = (struct fastrpc_user *)file->private_data;
>  	struct fastrpc_channel_ctx *cctx = fl->cctx;
> +	struct fastrpc_invoke_ctx *ctx, *n;
>  	unsigned long flags;
>  
>  	fastrpc_release_current_dsp_process(fl);
> @@ -1733,6 +1813,18 @@ static int fastrpc_device_release(struct inode *inode, struct file *file)
>  	list_del(&fl->user);
>  	spin_unlock_irqrestore(&cctx->lock, flags);
>  
> +	/* fl is already unlinked from cctx->users; drop the invoker's ref so it isn't leaked. */
> +	spin_lock(&fl->lock);
> +	list_for_each_entry_safe(ctx, n, &fl->interrupted, node) {
> +		list_del_init(&ctx->node);
same comment here

> +		ctx->retval = -EPIPE;
> +		complete(&ctx->work);
> +		spin_unlock(&fl->lock);
> +		fastrpc_context_put(ctx);
> +		spin_lock(&fl->lock);
> +	}
> +	spin_unlock(&fl->lock);
> +
>  	fastrpc_session_free(cctx, fl->sctx);
>  	file->private_data = NULL;
>  	/* Release the reference taken in fastrpc_device_open */
> @@ -1762,6 +1854,7 @@ 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);
> @@ -1871,6 +1964,7 @@ static int fastrpc_invoke(struct fastrpc_user *fl, char __user *argp)
>  	}
>  
>  	err = fastrpc_internal_invoke(fl, false, inv.handle, inv.sc, args);
> +	/* ctx keeps its own copy of args, so this is always safe to free. */
>  	kfree(args);
>  
>  	return err;
> @@ -2636,7 +2730,6 @@ 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;
> @@ -2669,13 +2762,22 @@ static void fastrpc_notify_users(struct fastrpc_user *user)
>  		ctx->retval = -EPIPE;
>  		complete(&ctx->work);
>  	}
> +
> +	/* Drops only 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);
> +		if (!ctx->put_work_scheduled) {
> +			ctx->put_work_scheduled = true;
> +			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;
>  
> @@ -2692,9 +2794,6 @@ 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_size && cctx->vmcount) {
>  		u64 src_perms = 0;
>  		int err, i;
> @@ -2778,9 +2877,11 @@ static int fastrpc_rpmsg_callback(struct rpmsg_device *rpdev, void *data,
>  	/*
>  	 * 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.
> +	 * avoid a kernel BUG. fastrpc_context_schedule_put_work() guards
> +	 * against a concurrent fastrpc_notify_users() also scheduling this
> +	 * same work item for an interrupted context.
>  	 */
> -	schedule_work(&ctx->put_work);
> +	fastrpc_context_schedule_put_work(ctx);
>  
>  	return 0;
>  }
> 
> ---
> base-commit: ef071c4906eb45d16b60f09154cf0bc6ec8f5435
> change-id: 20260930-anandu-fastrpc-interrupted-invoke-v3-10b130c444f1
> 
> Best regards,
> --  
> Anandu Krishnan E <anandu.e@oss.qualcomm.com>