[PATCH] [RESEND] media: don't drop front-end reference count for ->detach

From: Arnd Bergmann
Date: Mon Mar 04 2019 - 15:45:42 EST

A bugfix introduce a link failure in configurations without CONFIG_MODULES:

In file included from drivers/media/usb/dvb-usb/pctv452e.c:20:0:
drivers/media/usb/dvb-usb/pctv452e.c: In function 'pctv452e_frontend_attach':
drivers/media/dvb-frontends/stb0899_drv.h:151:36: error: weak declaration of 'stb0899_attach' being applied to a already existing, static definition

The problem is that the !IS_REACHABLE() declaration of stb0899_attach()
is a 'static inline' definition that clashes with the weak definition.

I further observed that the bugfix was only done for one of the five users
of stb0899_attach(), the other four still have the problem. This reverts
the bugfix and instead addresses the problem by not dropping the reference
count when calling '->detach()', instead we call this function directly
in dvb_frontend_put() before dropping the kref on the front-end.

I first submitted this in early 2018, and after some discussion it
was apparently discarded. While there is a long-term plan in place,
that plan is obviously not nearing completion yet, and the current
kernel is still broken unless this patch is applied.

Cc: Max Kellermann <max.kellermann@xxxxxxxxx>
Cc: Wolfgang Rohdewald <wolfgang@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: f686c14364ad ("[media] stb0899: move code to "detach" callback")
Fixes: 6cdeaed3b142 ("media: dvb_usb_pctv452e: module refcount changes were unbalanced")
Link: https://patchwork.kernel.org/patch/10140175/
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
drivers/media/dvb-core/dvb_frontend.c | 4 +++-
drivers/media/usb/dvb-usb/pctv452e.c | 8 --------
2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index fbdb4ecc7c50..eb5da50ff95e 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -164,6 +164,9 @@ static void dvb_frontend_free(struct kref *ref)

static void dvb_frontend_put(struct dvb_frontend *fe)
+ /* call detach before dropping the reference count */
+ if (fe->ops.detach)
+ fe->ops.detach(fe);
* Check if the frontend was registered, as otherwise
* kref was not initialized yet.
@@ -3038,7 +3041,6 @@ void dvb_frontend_detach(struct dvb_frontend *fe)
dvb_frontend_invoke_release(fe, fe->ops.release_sec);
dvb_frontend_invoke_release(fe, fe->ops.tuner_ops.release);
dvb_frontend_invoke_release(fe, fe->ops.analog_ops.release);
- dvb_frontend_invoke_release(fe, fe->ops.detach);
diff --git a/drivers/media/usb/dvb-usb/pctv452e.c b/drivers/media/usb/dvb-usb/pctv452e.c
index 150081128196..5c653b660272 100644
--- a/drivers/media/usb/dvb-usb/pctv452e.c
+++ b/drivers/media/usb/dvb-usb/pctv452e.c
@@ -913,14 +913,6 @@ static int pctv452e_frontend_attach(struct dvb_usb_adapter *a)
if (!a->fe_adap[0].fe)
return -ENODEV;
- /*
- * dvb_frontend will call dvb_detach for both stb0899_detach
- * and stb0899_release but we only do dvb_attach(stb0899_attach).
- * Increment the module refcount instead.
- */
- symbol_get(stb0899_attach);
if ((dvb_attach(lnbp22_attach, a->fe_adap[0].fe,
&a->dev->i2c_adap)) == NULL)
err("Cannot attach lnbp22\n");