linux-kernel - [PATCH] usb: gadget: f_fs: Ensure io_completion

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Date:   Fri, 21 May 2021 17:44:21 -0700
From:   Wesley Cheng <wcheng@...eaurora.org>
To:     balbi@...nel.org, gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        jackp@...eaurora.org, Wesley Cheng <wcheng@...eaurora.org>
Subject: [PATCH] usb: gadget: f_fs: Ensure io_completion_wq is idle during unbind

During unbind, ffs_func_eps_disable() will be executed, resulting in
completion callbacks for any pending USB requests.  When using AIO,
irrespective of the completion status, io_data work is queued to
io_completion_wq to evaluate and handle the completed requests.  Since
work runs asynchronously to the unbind() routine, there can be a
scenario where the work runs after the USB gadget has been fully
removed, resulting in accessing of a resource which has been already
freed. (i.e. usb_ep_free_request() accessing the USB ep structure)

Explicitly drain the io_completion_wq, instead of relying on the
destroy_workqueue() (in ffs_data_put()) to make sure no pending
completion work items are running.

Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>
---
 drivers/usb/gadget/function/f_fs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index bf10919..d4844af 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -3567,6 +3567,9 @@ static void ffs_func_unbind(struct usb_configuration *c,
 		ffs->func = NULL;
 	}

+	/* Drain any pending AIO completions */
+	drain_workqueue(ffs->io_completion_wq);
+
 	if (!--opts->refcnt)
 		functionfs_unbind(ffs);

-- 
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