[PATCH] [media] dvb-frontends/stv0910: prevent consecutive mutex_unlock()'s

[Daniel Scheller]

From: Daniel Scheller <d.schel...@gmx.net>

When calling gate_ctrl() with enable=0 if previously the mutex wasn't
locked (ie. on enable=1 failure and subdrivers not handling this properly,
or by otherwise badly behaving drivers), the i2c_lock could be unlocked
consecutively which isn't allowed. Prevent this by keeping track of the
lock state, and actually call mutex_unlock() only when certain the lock
is held.

Signed-off-by: Daniel Scheller <d.schel...@gmx.net>
Tested-by: Jasmin Jessich <jas...@anw.at>
---
 drivers/media/dvb-frontends/stv0910.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/media/dvb-frontends/stv0910.c 
b/drivers/media/dvb-frontends/stv0910.c
index 73f6df0abbfe..36ef96ec64c1 100644
--- a/drivers/media/dvb-frontends/stv0910.c
+++ b/drivers/media/dvb-frontends/stv0910.c
@@ -80,6 +80,7 @@ struct stv_base {
        u8                   adr;
        struct i2c_adapter  *i2c;
        struct mutex         i2c_lock; /* shared I2C access protect */
+       u8                   i2c_islocked; /* I2C lock state */
        struct mutex         reg_lock; /* shared register write protect */
        int                  count;
 
@@ -1233,6 +1234,7 @@ static int gate_ctrl(struct dvb_frontend *fe, int enable)
 
        if (enable) {
                mutex_lock(&state->base->i2c_lock);
+               state->base->i2c_islocked = 1;
                i2crpt |= 0x80;
        } else {
                i2crpt |= 0x02;
@@ -1240,8 +1242,15 @@ static int gate_ctrl(struct dvb_frontend *fe, int enable)
 
        if (write_reg(state, state->nr ? RSTV0910_P2_I2CRPT :
                      RSTV0910_P1_I2CRPT, i2crpt) < 0) {
-               /* don't hold the I2C bus lock on failure */
-               mutex_unlock(&state->base->i2c_lock);
+               /*
+                * don't hold the I2C bus lock on failure while preventing
+                * consecutive and disallowed calls to mutex_unlock()
+                */
+               if (state->base->i2c_islocked) {
+                       state->base->i2c_islocked = 0;
+                       mutex_unlock(&state->base->i2c_lock);
+               }
+
                dev_err(&state->base->i2c->dev,
                        "%s() write_reg failure (enable=%d)\n",
                        __func__, enable);
@@ -1250,8 +1259,13 @@ static int gate_ctrl(struct dvb_frontend *fe, int enable)
 
        state->i2crpt = i2crpt;
 
-       if (!enable)
-               mutex_unlock(&state->base->i2c_lock);
+       if (!enable) {
+               if (state->base->i2c_islocked) {
+                       state->base->i2c_islocked = 0;
+                       mutex_unlock(&state->base->i2c_lock);
+               }
+       }
+
        return 0;
 }
 
@@ -1795,6 +1809,7 @@ struct dvb_frontend *stv0910_attach(struct i2c_adapter 
*i2c,
 
                mutex_init(&base->i2c_lock);
                mutex_init(&base->reg_lock);
+               base->i2c_islocked = 0;
                state->base = base;
                if (probe(state) < 0) {
                        dev_info(&i2c->dev, "No demod found at adr %02X on 
%s\n",
-- 
2.13.6