The process spin lock currently has the following distinct uses:

- Threads lifetime cycle, in particular, counting of the threads in
  the process, and interlocking with process mutex and thread lock.
  The main reason of this is that turnstile locks are after thread
  locks, so you e.g. cannot unlock blockable mutex (think process
  mutex) while owning thread lock.

- Virtual and profiling itimers, since the timers activation is done
  from the clock interrupt context.  Replace the p_slock by p_itimmtx
  and PROC_ITIMLOCK().

- Profiling code (profil(2)), for similar reason.  Replace the p_slock
  by p_profmtx and PROC_PROFLOCK().

- Resource usage accounting.  Need for the spinlock there is subtle,
  my understanding is that spinlock blocks context switching for the
  current thread, which prevents td_runtime and similar fields from
  changing (updates are done at the mi_switch()).  Replace the p_slock
  by p_statmtx and PROC_STATLOCK().

The split is done mostly for code clarity, and should not affect
scalability.

Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

1 files changed, 7 insertions, 6 deletions

diff --git a/sys/sys/resourcevar.h b/sys/sys/resourcevar.h
index a24e89a..a07fdf8 100644
--- a/sys/sys/resourcevar.h
+++ b/sys/sys/resourcevar.h
@@ -47,21 +47,22 @@
  * Locking key:
  *      b - created at fork, never changes
  *      c - locked by proc mtx
- *      j - locked by proc slock
  *      k - only accessed by curthread
+ *      w - locked by proc itim lock
+ *	w2 - locked by proc prof lock
  */
 struct pstats {
 #define	pstat_startzero	p_cru
 	struct	rusage p_cru;		/* Stats for reaped children. */
-	struct	itimerval p_timer[3];	/* (j) Virtual-time timers. */
+	struct	itimerval p_timer[3];	/* (w) Virtual-time timers. */
 #define	pstat_endzero	pstat_startcopy
 
 #define	pstat_startcopy	p_prof
 	struct uprof {			/* Profile arguments. */
-		caddr_t	pr_base;	/* (c + j) Buffer base. */
-		u_long	pr_size;	/* (c + j) Buffer size. */
-		u_long	pr_off;		/* (c + j) PC offset. */
-		u_long	pr_scale;	/* (c + j) PC scaling. */
+		caddr_t	pr_base;	/* (c + w2) Buffer base. */
+		u_long	pr_size;	/* (c + w2) Buffer size. */
+		u_long	pr_off;		/* (c + w2) PC offset. */
+		u_long	pr_scale;	/* (c + w2) PC scaling. */
 	} p_prof;
 #define	pstat_endcopy	p_start
 	struct	timeval p_start;	/* (b) Starting time. */