svn commit: r241071 - stable/9/sys/kern

[Konstantin Belousov]

Author: kib
Date: Sun Sep 30 13:32:48 2012
New Revision: 241071
URL: http://svn.freebsd.org/changeset/base/241071

Log:
  MFC r240813:
  Do not skip two elements of the tid_buffer when reusing the buffer
  slot. This eventually results in exhaustion of the tid space, causing
  new threads get tid -1 as identifier.
  
  MFC r240951:
  Make the updates of the tid ring buffer' head and tail pointers
  explicit by moving them into separate statements from the buffer
  element accesses.

Modified:
  stable/9/sys/kern/kern_thread.c
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/9/sys/kern/kern_thread.c
==============================================================================
--- stable/9/sys/kern/kern_thread.c	Sun Sep 30 13:17:33 2012	(r241070)
+++ stable/9/sys/kern/kern_thread.c	Sun Sep 30 13:32:48 2012	(r241071)
@@ -102,8 +102,8 @@ tid_alloc(void)
 		mtx_unlock(&tid_lock);
 		return (-1);
 	}
-	tid = tid_buffer[tid_head++];
-	tid_head %= TID_BUFFER_SIZE;
+	tid = tid_buffer[tid_head];
+	tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
 	mtx_unlock(&tid_lock);
 	return (tid);
 }
@@ -115,11 +115,11 @@ tid_free(lwpid_t tid)
 
 	mtx_lock(&tid_lock);
 	if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
-		tmp_tid = tid_buffer[tid_head++];
+		tmp_tid = tid_buffer[tid_head];
 		tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
 	}
-	tid_buffer[tid_tail++] = tid;
-	tid_tail %= TID_BUFFER_SIZE;
+	tid_buffer[tid_tail] = tid;
+	tid_tail = (tid_tail + 1) % TID_BUFFER_SIZE;
 	mtx_unlock(&tid_lock);
 	if (tmp_tid != -1)
 		free_unr(tid_unrhdr, tmp_tid);