Re: [PATCH 3/5] hw_random: fix unregister race.
On Tue, Oct 21, 2014 at 10:15:23PM +0800, Herbert Xu wrote: > On Thu, Sep 18, 2014 at 12:18:24PM +0930, Rusty Russell wrote: > > The previous patch added one potential problem: we can still be > > reading from a hwrng when it's unregistered. Add a wait for zero > > in the hwrng_unregister path. > > > > Signed-off-by: Rusty Russell > > --- > > drivers/char/hw_random/core.c | 5 + > > 1 file changed, 5 insertions(+) > > > > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c > > index dc9092a1075d..b4a21e9521cf 100644 > > --- a/drivers/char/hw_random/core.c > > +++ b/drivers/char/hw_random/core.c > > @@ -60,6 +60,7 @@ static DEFINE_MUTEX(rng_mutex); > > static DEFINE_MUTEX(reading_mutex); > > static int data_avail; > > static u8 *rng_buffer, *rng_fillbuf; > > +static DECLARE_WAIT_QUEUE_HEAD(rng_done); > > static unsigned short current_quality; > > static unsigned short default_quality; /* = 0; default to "off" */ > > > > @@ -98,6 +99,7 @@ static inline void cleanup_rng(struct kref *kref) > > > > if (rng->cleanup) > > rng->cleanup(rng); rng->cleanup_done = true; > > + wake_up_all(&rng_done); > > } > > > > static void set_current_rng(struct hwrng *rng) > > @@ -529,6 +531,9 @@ void hwrng_unregister(struct hwrng *rng) > > } > > > > mutex_unlock(&rng_mutex); > > + > > + /* Just in case rng is reading right now, wait. */ > > + wait_event(rng_done, atomic_read(&rng->ref.refcount) == 0); Hi Rusty, After initializing (kref_init()), the refcount is 1, so we need one more kref_put() after each drop_current_rng() to release last reference count, then cleanup function will be called. > While it's obviously better than what we have now, I don't believe > this is 100% safe as the cleanup function might still be running > even after the ref count hits zero. Once we return from this function > the module may be unloaded so we need to ensure that nothing is > running at this point. I found wait_event() can still pass and finish unregister even cleanup function isn't called (wake_up_all() isn't called). So I added a flag cleanup_done to indicate that the rng device is cleaned up. + /* Just in case rng is reading right now, wait. */ + wait_event(rng_done, rng->cleanup_done && + atomic_read(&rng->ref.refcount) == 0); I will post the new v4 later. > Cheers, > -- > Email: Herbert Xu > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- Amos. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 3/5] hw_random: fix unregister race.
On Thu, Sep 18, 2014 at 12:18:24PM +0930, Rusty Russell wrote: > The previous patch added one potential problem: we can still be > reading from a hwrng when it's unregistered. Add a wait for zero > in the hwrng_unregister path. > > Signed-off-by: Rusty Russell > --- > drivers/char/hw_random/core.c | 5 + > 1 file changed, 5 insertions(+) > > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c > index dc9092a1075d..b4a21e9521cf 100644 > --- a/drivers/char/hw_random/core.c > +++ b/drivers/char/hw_random/core.c > @@ -60,6 +60,7 @@ static DEFINE_MUTEX(rng_mutex); > static DEFINE_MUTEX(reading_mutex); > static int data_avail; > static u8 *rng_buffer, *rng_fillbuf; > +static DECLARE_WAIT_QUEUE_HEAD(rng_done); > static unsigned short current_quality; > static unsigned short default_quality; /* = 0; default to "off" */ > > @@ -98,6 +99,7 @@ static inline void cleanup_rng(struct kref *kref) > > if (rng->cleanup) > rng->cleanup(rng); > + wake_up_all(&rng_done); > } > > static void set_current_rng(struct hwrng *rng) > @@ -529,6 +531,9 @@ void hwrng_unregister(struct hwrng *rng) > } > > mutex_unlock(&rng_mutex); > + > + /* Just in case rng is reading right now, wait. */ > + wait_event(rng_done, atomic_read(&rng->ref.refcount) == 0); While it's obviously better than what we have now, I don't believe this is 100% safe as the cleanup function might still be running even after the ref count hits zero. Once we return from this function the module may be unloaded so we need to ensure that nothing is running at this point. Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH 3/5] hw_random: fix unregister race.
The previous patch added one potential problem: we can still be reading from a hwrng when it's unregistered. Add a wait for zero in the hwrng_unregister path. Signed-off-by: Rusty Russell --- drivers/char/hw_random/core.c | 5 + 1 file changed, 5 insertions(+) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index dc9092a1075d..b4a21e9521cf 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -60,6 +60,7 @@ static DEFINE_MUTEX(rng_mutex); static DEFINE_MUTEX(reading_mutex); static int data_avail; static u8 *rng_buffer, *rng_fillbuf; +static DECLARE_WAIT_QUEUE_HEAD(rng_done); static unsigned short current_quality; static unsigned short default_quality; /* = 0; default to "off" */ @@ -98,6 +99,7 @@ static inline void cleanup_rng(struct kref *kref) if (rng->cleanup) rng->cleanup(rng); + wake_up_all(&rng_done); } static void set_current_rng(struct hwrng *rng) @@ -529,6 +531,9 @@ void hwrng_unregister(struct hwrng *rng) } mutex_unlock(&rng_mutex); + + /* Just in case rng is reading right now, wait. */ + wait_event(rng_done, atomic_read(&rng->ref.refcount) == 0); } EXPORT_SYMBOL_GPL(hwrng_unregister); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
