MFC r312153, r312191

r312153:

  For i386 temporary mappings, unpin the thread before releasing
  the cmap lock.  Releasing the lock first may result in the thread
  being immediately rescheduled and bound to the same CPU, only to
  unpin itself upon resuming execution.

  Noted by:	skra (in review for armv6 equivalent)

r312191:

  Add comment explaining relative order of sched_unpin() and mtx_unlock().

  Suggested by:	alc

1 files changed, 11 insertions, 5 deletions

diff --git a/sys/i386/i386/pmap.c b/sys/i386/i386/pmap.c
index 83f1bbf..d717876 100644
--- a/sys/i386/i386/pmap.c
+++ b/sys/i386/i386/pmap.c
@@ -4231,8 +4231,14 @@ pmap_zero_page(vm_page_t m)
 	invlcaddr(pc->pc_cmap_addr2);
 	pagezero(pc->pc_cmap_addr2);
 	*cmap_pte2 = 0;
-	mtx_unlock(&pc->pc_cmap_lock);
+
+	/*
+	 * Unpin the thread before releasing the lock.  Otherwise the thread
+	 * could be rescheduled while still bound to the current CPU, only
+	 * to unpin itself immediately upon resuming execution.
+	 */
 	sched_unpin();
+	mtx_unlock(&pc->pc_cmap_lock);
 }
 
 /*
@@ -4261,8 +4267,8 @@ pmap_zero_page_area(vm_page_t m, int off, int size)
 	else
 		bzero(pc->pc_cmap_addr2 + off, size);
 	*cmap_pte2 = 0;
-	mtx_unlock(&pc->pc_cmap_lock);
 	sched_unpin();
+	mtx_unlock(&pc->pc_cmap_lock);
 }
 
 /*
@@ -4316,8 +4322,8 @@ pmap_copy_page(vm_page_t src, vm_page_t dst)
 	bcopy(pc->pc_cmap_addr1, pc->pc_cmap_addr2, PAGE_SIZE);
 	*cmap_pte1 = 0;
 	*cmap_pte2 = 0;
-	mtx_unlock(&pc->pc_cmap_lock);
 	sched_unpin();
+	mtx_unlock(&pc->pc_cmap_lock);
 }
 
 int unmapped_buf_allowed = 1;
@@ -4364,8 +4370,8 @@ pmap_copy_pages(vm_page_t ma[], vm_offset_t a_offset, vm_page_t mb[],
 	}
 	*cmap_pte1 = 0;
 	*cmap_pte2 = 0;
-	mtx_unlock(&pc->pc_cmap_lock);
 	sched_unpin();
+	mtx_unlock(&pc->pc_cmap_lock);
 }
 
 /*
@@ -5349,8 +5355,8 @@ pmap_flush_page(vm_page_t m)
 		if (useclflushopt || cpu_vendor_id != CPU_VENDOR_INTEL)
 			mfence();
 		*cmap_pte2 = 0;
-		mtx_unlock(&pc->pc_cmap_lock);
 		sched_unpin();
+		mtx_unlock(&pc->pc_cmap_lock);
 	} else
 		pmap_invalidate_cache();
 }