Hi Dave,
I just found this patch, which does not seem to be a correct solution
to solve a race.
Maybe there is really an issue with the refcounting of data->kref, but
currently I do
not have time to check this in home office.
At least I see a problem in usbtmc_probe()
After calling:
/* Protect interrupt in endpoint data until iin_urb is freed */
kref_get(&data->kref);
the refcounter is incremented again and if usbtmc_probe() fails, the
counter is
only decremented with a single kref_put(..).
I don't know if this is the reason of Lv Yunglong's problem, but let
me know if
you have time to track down this issue, and we will work on a correct
and tested
patch.
Regards,
Guido
-----Original Message-----
From: Greg KH
Sent: Tuesday, March 23, 2021 10:44 AM
To: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
Cc: linux-usb@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v2] usb: Add a lock when freeing data in
usbtmc_disconnect
On Tue, Mar 23, 2021 at 02:28:54AM -0700, Lv Yunlong wrote:
In usbtmc_disconnect, data is got from intf with the initial reference.
There is no refcount inc operation before usbmc_free_int(data). In
usbmc_free_int(data), the data may be freed.
But later in usbtmc_disconnect, there is another put function of data.
It could cause errors in race.
My patch adds a lock to protect kref from changing in race.
Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
---
drivers/usb/class/usbtmc.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
index 74d5a9c5238a..44f1fcabbb1e 100644
--- a/drivers/usb/class/usbtmc.c
+++ b/drivers/usb/class/usbtmc.c
@@ -2493,8 +2493,13 @@ static void usbtmc_disconnect(struct
usb_interface *intf)
usb_scuttle_anchored_urbs(&file_data->in_anchor);
}
mutex_unlock(&data->io_mutex);
+
+ spinlock_t *dev_lock = &data->dev_lock;
+
+ spin_lock_irq(dev_lock);
usbtmc_free_int(data);
kref_put(&data->kref, usbtmc_delete);
+ spin_unlock_irq(dev_lock);
}
static void usbtmc_draw_down(struct usbtmc_file_data *file_data)
--
2.25.1
You obviously did not even build this patch, let alone test it :(
Please do not waste maintainer's time by not doing the proper steps
when submitting patches.
thanks,
greg k-h
