NAME¶

struct_fence - software synchronization primitive

SYNOPSIS¶

struct fence {
  struct kref refcount;
  const struct fence_ops * ops;
  struct rcu_head rcu;
  struct list_head cb_list;
  spinlock_t * lock;
  u64 context;
  unsigned seqno;
  unsigned long flags;
  ktime_t timestamp;
  int status;
};  

MEMBERS¶

refcount ops rcu cb_list lock context seqno flags timestamp status

DESCRIPTION¶

the flags member must be manipulated and read using the appropriate atomic ops (bit_*), so taking the spinlock will not be needed most of the time. FENCE_FLAG_SIGNALED_BIT - fence is already signaled FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called* FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the implementer of the fence for its own purposes. Can be used in different ways by different fence implementers, so do not rely on this. *) Since atomic bitops are used, this is not guaranteed to be the case. Particularly, if the bit was set, but fence_signal was called right before this bit was set, it would have been able to set the FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called. Adding a check for FENCE_FLAG_SIGNALED_BIT after setting FENCE_FLAG_ENABLE_SIGNAL_BIT closes this race, and makes sure that after fence_signal was called, any enable_signaling call will have either been completed, or never called at all.

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