svn commit: r263309 - in stable: 8/sys/fs/fifofs 9/sys/fs/fifofs

[John Baldwin]

Author: jhb
Date: Tue Mar 18 17:17:42 2014
New Revision: 263309
URL: http://svnweb.freebsd.org/changeset/base/263309

Log:
  Increment fi_wgen before awakening threads polling the read socket of a
  FIFO.  Previously, a thread sleeping in poll() could be awakened and
  re-poll the FIFO with the old value of fi_wgen (and thus improperly
  setting POLLINIGNEOF) before a thread closing a writable fifo descriptor
  bumped fi_wgen.  The end result was that the reading thread in poll()
  would never see POLLHUP but could block forever (or until a timeout).
  
  This is a direct commit to 8 and 9 since the FIFO code is implemented
  differently in 10.x and later.  The pipe-backed FIFOs in 10 do not have
  this bug.

Modified:
  stable/9/sys/fs/fifofs/fifo_vnops.c

Changes in other areas also in this revision:
Modified:
  stable/8/sys/fs/fifofs/fifo_vnops.c

Modified: stable/9/sys/fs/fifofs/fifo_vnops.c
==============================================================================
--- stable/9/sys/fs/fifofs/fifo_vnops.c	Tue Mar 18 17:00:32 2014	(r263308)
+++ stable/9/sys/fs/fifofs/fifo_vnops.c	Tue Mar 18 17:17:42 2014	(r263309)
@@ -294,10 +294,10 @@ fail1:
 			if (error) {
 				fip->fi_writers--;
 				if (fip->fi_writers == 0) {
-					socantrcvmore(fip->fi_readsock);
 					mtx_lock(&fifo_mtx);
 					fip->fi_wgen++;
 					mtx_unlock(&fifo_mtx);
+					socantrcvmore(fip->fi_readsock);
 					fifo_cleanup(vp);
 				}
 				return (error);
@@ -415,10 +415,10 @@ fifo_close(ap)
 	if (ap->a_fflag & FWRITE) {
 		fip->fi_writers--;
 		if (fip->fi_writers == 0) {
-			socantrcvmore(fip->fi_readsock);
 			mtx_lock(&fifo_mtx);
 			fip->fi_wgen++;
 			mtx_unlock(&fifo_mtx);
+			socantrcvmore(fip->fi_readsock);
 		}
 	}
 	fifo_cleanup(vp);