Add PROC_COW_CHANGECOUNT and thread_cow_synced

Combined they can be used to avoid a proc lock/unlock cycle in the
syscall handler for curthread, see upcoming examples.

2 files changed, 22 insertions, 0 deletions

diff --git a/sys/kern/kern_thread.c b/sys/kern/kern_thread.c
index dcb52b137b58..bb724a17803e 100644
--- a/sys/kern/kern_thread.c
+++ b/sys/kern/kern_thread.c
@@ -868,6 +868,19 @@ thread_cow_update(struct thread *td)
 		lim_free(oldlimit);
 }
 
+void
+thread_cow_synced(struct thread *td)
+{
+	struct proc *p;
+
+	p = td->td_proc;
+	PROC_LOCK_ASSERT(p, MA_OWNED);
+	MPASS(td->td_cowgen != p->p_cowgen);
+	MPASS(td->td_ucred == p->p_ucred);
+	MPASS(td->td_limit == p->p_limit);
+	td->td_cowgen = p->p_cowgen;
+}
+
 /*
  * Discard the current thread and exit from its context.
  * Always called with scheduler locked.
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index ff97bfbd54a9..0e33192303f4 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -1009,6 +1009,14 @@ extern pid_t pid_max;
 	(p)->p_cowgen++;						\
 } while (0)
 
+#define	PROC_COW_CHANGECOUNT(td, p) ({					\
+	struct thread *_td = (td);					\
+	struct proc *_p = (p);						\
+	MPASS(_td == curthread);					\
+	PROC_LOCK_ASSERT(_p, MA_OWNED);					\
+	_p->p_cowgen - _td->td_cowgen;					\
+})
+
 /* Check whether a thread is safe to be swapped out. */
 #define	thread_safetoswapout(td)	((td)->td_flags & TDF_CANSWAP)
 
@@ -1200,6 +1208,7 @@ void	thread_cow_get_proc(struct thread *newtd, struct proc *p);
 void	thread_cow_get(struct thread *newtd, struct thread *td);
 void	thread_cow_free(struct thread *td);
 void	thread_cow_update(struct thread *td);
+void	thread_cow_synced(struct thread *td);
 int	thread_create(struct thread *td, struct rtprio *rtp,
 	    int (*initialize_thread)(struct thread *, void *), void *thunk);
 void	thread_exit(void) __dead2;