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From: Mikolaj Golub <trociny@FreeBSD.org>
Date: Sun, 29 May 2011 18:00:50 +0000 (UTC)
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Subject: svn commit: r222454 - head/sys/kern
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Author: trociny
Date: Sun May 29 18:00:50 2011
New Revision: 222454
URL: http://svn.freebsd.org/changeset/base/222454

Log:
  In soreceive_generic(), if MSG_WAITALL is set but the request is
  larger than the receive buffer, we have to receive in sections.
  When notifying the protocol that some data has been drained the
  lock is released for a moment. Returning we block waiting for the
  rest of data. There is a race, when data could arrive while the
  lock was released and then the connection stalls in sbwait.
  
  Fix this by checking for data before blocking and skip blocking
  if there are some.
  
  PR:		kern/154504
  Reported by:	Andrey Simonenko <simon@comsys.ntu-kpi.kiev.ua>
  Tested by:	Andrey Simonenko <simon@comsys.ntu-kpi.kiev.ua>
  Reviewed by:	rwatson
  Approved by:	kib (co-mentor)
  MFC after:	2 weeks

Modified:
  head/sys/kern/uipc_socket.c

Modified: head/sys/kern/uipc_socket.c
==============================================================================
--- head/sys/kern/uipc_socket.c	Sun May 29 15:10:12 2011	(r222453)
+++ head/sys/kern/uipc_socket.c	Sun May 29 18:00:50 2011	(r222454)
@@ -1845,10 +1845,16 @@ dontblock:
 			}
 			SBLASTRECORDCHK(&so->so_rcv);
 			SBLASTMBUFCHK(&so->so_rcv);
-			error = sbwait(&so->so_rcv);
-			if (error) {
-				SOCKBUF_UNLOCK(&so->so_rcv);
-				goto release;
+			/*
+			 * We could receive some data while was notifying
+			 * the protocol. Skip blocking in this case.
+			 */
+			if (so->so_rcv.sb_mb == NULL) {
+				error = sbwait(&so->so_rcv);
+				if (error) {
+					SOCKBUF_UNLOCK(&so->so_rcv);
+					goto release;
+				}
 			}
 			m = so->so_rcv.sb_mb;
 			if (m != NULL)