Index: sparc/cpu.c
===================================================================
RCS file: /cvsroot/src/sys/arch/sparc/sparc/cpu.c,v
retrieving revision 1.225
diff -p -r1.225 cpu.c
*** sparc/cpu.c	22 Jan 2011 12:13:25 -0000	1.225
--- sparc/cpu.c	26 Jan 2011 10:38:34 -0000
*************** cpu_init_evcnt(struct cpu_info *cpi)
*** 301,314 ****
  {
  
  	/*
! 	 * Setup the per-cpu savefpstate counters.  The "savefp null"
! 	 * counter should go away when the NULL struct fpstate * bug
! 	 * is fixed.
  	 */
  	evcnt_attach_dynamic(&cpi->ci_savefpstate, EVCNT_TYPE_MISC,
  			     NULL, cpu_name(cpi), "savefp ipi");
  	evcnt_attach_dynamic(&cpi->ci_savefpstate_null, EVCNT_TYPE_MISC,
  			     NULL, cpu_name(cpi), "savefp null ipi");
  }
  
  /*
--- 301,319 ----
  {
  
  	/*
! 	 * Setup the per-cpu counters.
! 	 *
! 	 * The "savefp null" counter should go away when the NULL
! 	 * struct fpstate * bug is fixed.
  	 */
  	evcnt_attach_dynamic(&cpi->ci_savefpstate, EVCNT_TYPE_MISC,
  			     NULL, cpu_name(cpi), "savefp ipi");
  	evcnt_attach_dynamic(&cpi->ci_savefpstate_null, EVCNT_TYPE_MISC,
  			     NULL, cpu_name(cpi), "savefp null ipi");
+ 	evcnt_attach_dynamic(&cpi->ci_xpmsg_mutex_fail, EVCNT_TYPE_MISC,
+ 			     NULL, cpu_name(cpi), "IPI mutex_trylock fail");
+ 	evcnt_attach_dynamic(&cpi->ci_xpmsg_mutex_fail_call, EVCNT_TYPE_MISC,
+ 			     NULL, cpu_name(cpi), "IPI mutex_trylock fail with call");
  }
  
  /*
*************** xcall(xcall_func_t func, xcall_trap_t tr
*** 592,598 ****
--- 597,633 ----
  	cpuset &= cpu_ready_mask;
  
  	/* prevent interrupts that grab the kernel lock */
+ #if 0
  	mutex_spin_enter(&xpmsg_mutex);
+ #else
+ 	/*
+ 	 * There's a deadlock potential between multiple CPUs trying
+ 	 * to xcall() at the same time, and the thread that loses the
+ 	 * race to get xpmsg_lock is at an IPL above the incoming IPI
+ 	 * IPL level, so it sits around waiting to take the lock while
+ 	 * the other CPU is waiting for this CPU to handle the IPI and
+ 	 * mark it as completed.
+ 	 *
+ 	 * If we fail to get the mutex, and we're at high enough IPL,
+ 	 * call xcallintr() if there is a valid msg.tag.
+ 	 */
+     {
+ 	u_int pil = (getpsr() & PSR_PIL) >> 8;
+ 	
+ 	if (cold || pil < 13)
+ 		mutex_spin_enter(&xpmsg_mutex);
+ 	else {
+ 		while (mutex_tryenter(&xpmsg_mutex) == 0) {
+ 			void xcallintr(void *);
+ 			cpuinfo.ci_xpmsg_mutex_fail.ev_count++;
+ 			if (cpuinfo.msg.tag) {
+ 				cpuinfo.ci_xpmsg_mutex_fail_call.ev_count++;
+ 				xcallintr(NULL);
+ 			}
+ 		}
+ 	}
+     }
+ #endif
  
  	/*
  	 * Firstly, call each CPU.  We do this so that they might have
Index: sparc/cpuvar.h
===================================================================
RCS file: /cvsroot/src/sys/arch/sparc/sparc/cpuvar.h,v
retrieving revision 1.84
diff -p -r1.84 cpuvar.h
*** sparc/cpuvar.h	13 Jan 2011 05:20:27 -0000	1.84
--- sparc/cpuvar.h	26 Jan 2011 10:38:34 -0000
*************** struct cpu_info {
*** 340,345 ****
--- 340,347 ----
  	struct evcnt ci_lev14;
  	struct evcnt ci_savefpstate;
  	struct evcnt ci_savefpstate_null;
+ 	struct evcnt ci_xpmsg_mutex_fail;
+ 	struct evcnt ci_xpmsg_mutex_fail_call;
  };
  
  /*
Index: sparc/intr.c
===================================================================
RCS file: /cvsroot/src/sys/arch/sparc/sparc/intr.c,v
retrieving revision 1.109
diff -p -r1.109 intr.c
*** sparc/intr.c	22 Jan 2011 10:37:22 -0000	1.109
--- sparc/intr.c	26 Jan 2011 10:38:34 -0000
*************** nmi_soft(struct trapframe *tf)
*** 378,384 ****
  /*
   * Respond to an xcall() request from another CPU.
   */
! static void
  xcallintr(void *v)
  {
  
--- 378,385 ----
  /*
   * Respond to an xcall() request from another CPU.
   */
! void xcallintr(void *);
! /*static*/ void
  xcallintr(void *v)
  {