[CRIU] [PATCH v5 15/33] files: Implement {set, clear, wait}_fds_event()

[Andrei Vagin]

On Mon, Dec 26, 2016 at 05:27:08PM +0300, Kirill Tkhai wrote:
> The idea is symilar to kernel's wake_up() and wait_event().
> One task needs some event. It checks the event has not
> happened yet (fle hasn't received, unix peer hasn't bound, etc)
> and calls get_fds_event(). Other task makes the event
> (sends a fle, binds the peer to a name, etc) and calls set_fds_event().
> 
> So, while there is no an event, the first task is sleeping,
> and the second wakes it up later:
> 
> Task A:      clear_fds_event();
>              if (!socket_bound)
>                      wait_fds_event(); /* sleep */
> 
> Task B:      bind_socket();
>              set_fds_event();         /* wake up */
> 
> For the details of using see next patches.
> 
> v5: Use bit operations.
>     Split clear_fds_event from wait function.
> 
> v2: Do not wait for foreign transport sock is ready,
> as it's guarantied by we create it before CR_STATE_FORKING.
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/files.c          |   29 +++++++++++++++++++++++++++++
>  criu/include/files.h  |    2 ++
>  include/common/lock.h |    6 ++++++
>  3 files changed, 37 insertions(+)
> 
> diff --git a/criu/files.c b/criu/files.c
> index bff8880bf..87d8fc655 100644
> --- a/criu/files.c
> +++ b/criu/files.c
> @@ -149,6 +149,35 @@ unsigned int find_unused_fd(struct list_head *head, int hint_fd)
>  	return fd;
>  }
>  
> +int set_fds_event(pid_t virt)
> +{
> +	struct pstree_item *item;
> +	int old;
> +
> +	item = pstree_item_by_virt(virt);
> +	BUG_ON(!item);
> +
> +	old = test_and_set_bit(FDS_EVENT_BIT, (unsigned long *)&item->task_st);
> +
> +	if (!(old & FDS_EVENT))
> +		futex_wake(&item->task_st);
> +	return 0;
> +}
> +
> +void clear_fds_event(void)
> +{
> +	futex_t *f = &current->task_st;
> +
> +	clear_bit(FDS_EVENT_BIT, (unsigned long *)&f->raw.counter);

CID 174702 (#1 of 1): Out-of-bounds access (INCOMPATIBLE_CAST)
incompatible_cast: Pointer &f->raw.counter points to an object whose
effective type is int (32 bits, signed) but is dereferenced as a wider
unsigned long (64 bits, unsigned). This may lead to memory corruption.
[show details]

> +}
> +
> +void wait_fds_event(void)
> +{
> +	futex_t *f = &current->task_st;
> +
> +	futex_wait_if_cond(f, FDS_EVENT, &);
> +	clear_fds_event();
> +}
>  /*
>   * A file may be shared between several file descriptors. E.g
>   * when doing a fork() every fd of a forker and respective fds
> diff --git a/criu/include/files.h b/criu/include/files.h
> index 57190049d..1b44960de 100644
> --- a/criu/include/files.h
> +++ b/criu/include/files.h
> @@ -193,5 +193,7 @@ int dup_fle(struct pstree_item *task, struct fdinfo_list_entry *ple,
>  	    int fd, unsigned flags);
>  
>  extern int open_transport_socket(void);
> +extern int set_fds_event(pid_t virt);
> +extern void wait_fds_event(void);
>  
>  #endif /* __CR_FILES_H__ */
> diff --git a/include/common/lock.h b/include/common/lock.h
> index afc0f96d5..49b1af149 100644
> --- a/include/common/lock.h
> +++ b/include/common/lock.h
> @@ -78,6 +78,12 @@ static inline void futex_set_and_wake(futex_t *f, uint32_t v)
>  	LOCK_BUG_ON(sys_futex((uint32_t *)&f->raw.counter, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
>  }
>  
> +/* Wake up all futex @f waiters */
> +static inline void futex_wake(futex_t *f)
> +{
> +	LOCK_BUG_ON(sys_futex((uint32_t *)&f->raw.counter, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
> +}
> +
>  /* Mark futex @f as wait abort needed and wake up all waiters */
>  static inline void futex_abort_and_wake(futex_t *f)
>  {
> 
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