[CRIU] Re: [PATCH 1/2] futex: Make raw value being s32

[Andrew Vagin]

On Mon, Apr 02, 2012 at 10:20:47AM +0400, Cyrill Gorcunov wrote:
> In case of error we do set futex value to
> be negative one, this breaks waiting loops
> and allow us to exit from program.
> 
> But during the futex conversion futex_wait_while_gt
> was occasionally changed to u32 type making
> error conditions to yield endless wait loop.
> 
> Change futex raw value to s32 to fix this.
> 
> Reported-by: Andrey Vagin <avagin at openvz.org>
> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
>  include/lock.h |   22 +++++++++++-----------
>  1 files changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/include/lock.h b/include/lock.h
> index 6f77bfd..9d06da2 100644
> --- a/include/lock.h
> +++ b/include/lock.h
> @@ -12,7 +12,7 @@
>  #include "util.h"
>  
>  typedef struct {
> -	u32	raw;
> +	s32	raw;
>  } futex_t;
>  
>  /* Get current futex @f value */
> @@ -22,7 +22,7 @@ static inline u32 futex_get(futex_t *f)
>  }
>  
>  /* Set futex @f value to @v */
> -static inline void futex_set(futex_t *f, u32 v)
> +static inline void futex_set(futex_t *f, s32 v)
>  {
>  	atomic_set(&f->raw, v);
>  }
> @@ -33,30 +33,30 @@ static inline void futex_set(futex_t *f, u32 v)
>  #define futex_wait_if_cond(__f, __v, __cond)			\
>  	do {							\
>  		int ret;					\
> -		u32 tmp;					\
> +		s32 tmp;					\
>  								\
>  		while (1) {					\
>  			tmp = (__f)->raw;			\
>  			if (tmp __cond (__v))			\
>  				break;				\
> -			ret = sys_futex(&(__f)->raw, FUTEX_WAIT,\
> +			ret = sys_futex((u32 *)&(__f)->raw, FUTEX_WAIT,\
>  					tmp, NULL, NULL, 0);	\

I would prefer to change a prototype of sys_futex

>  			BUG_ON(ret < 0 && ret != -EWOULDBLOCK);	\
>  		}						\
>  	} while (0)
>  
>  /* Set futex @f to @v and wake up all waiters */
> -static inline void futex_set_and_wake(futex_t *f, u32 v)
> +static inline void futex_set_and_wake(futex_t *f, s32 v)
>  {
>  	atomic_set(&f->raw, v);
> -	BUG_ON(sys_futex(&f->raw, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
> +	BUG_ON(sys_futex((u32 *)&f->raw, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
>  }
>  
>  /* Decrement futex @f value and wake up all waiters */
>  static inline void futex_dec_and_wake(futex_t *f)
>  {
>  	atomic_dec(&f->raw);
> -	BUG_ON(sys_futex(&f->raw, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
> +	BUG_ON(sys_futex((u32 *)&f->raw, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
>  }
>  
>  /* Plain increment futex @f value */
> @@ -66,18 +66,18 @@ static inline void futex_inc(futex_t *f) { f->raw++; }
>  static inline void futex_dec(futex_t *f) { f->raw--; }
>  
>  /* Wait until futex @f value become @v */
> -static inline void futex_wait_until(futex_t *f, u32 v)
> +static inline void futex_wait_until(futex_t *f, s32 v)
>  { futex_wait_if_cond(f, v, ==); }
>  
>  /* Wait while futex @f value is greater than @v */
> -static inline void futex_wait_while_gt(futex_t *f, u32 v)
> +static inline void futex_wait_while_gt(futex_t *f, s32 v)
>  { futex_wait_if_cond(f, v, <=); }
>  
>  /* Wait while futex @f value is @v */
> -static inline void futex_wait_while(futex_t *f, u32 v)
> +static inline void futex_wait_while(futex_t *f, s32 v)
>  {
>  	while (f->raw == v) {
> -		int ret = sys_futex(&f->raw, FUTEX_WAIT, v, NULL, NULL, 0);
> +		int ret = sys_futex((u32 *)&f->raw, FUTEX_WAIT, v, NULL, NULL, 0);
>  		BUG_ON(ret < 0 && ret != -EWOULDBLOCK);
>  	}
>  }
> -- 
> 1.7.7.6
>