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Date:      Fri, 19 Dec 2008 15:24:18 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-7@freebsd.org
Subject:   svn commit: r186324 - in stable/7/sys: . contrib/pf dev/cxgb kern
Message-ID:  <200812191524.mBJFOIMj075547@svn.freebsd.org>
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Author: kib
Date: Fri Dec 19 15:24:18 2008
New Revision: 186324
URL: http://svn.freebsd.org/changeset/base/186324

Log:
  MFC r185983:
  The userland_sysctl() function retries sysctl_root() until returned
  error is not EAGAIN. Several sysctls that inspect another process use
  p_candebug() for checking access right for the curproc. p_candebug()
  returns EAGAIN for some reasons, in particular, for the process doing
  exec() now. If execing process tries to lock Giant, we get a livelock,
  because sysctl handlers are covered by Giant, and often do not sleep.
  
  Break the livelock by dropping Giant and allowing other threads to
  execute in the EAGAIN loop.
  
  This commit does not merge the following change, as was discussed with jhb:
  [Also, do not return EAGAIN from p_candebug() when process is executing,
  use more appropriate EBUSY error.]
  
  MFC r185987:
  Uio_yield() already does DROP_GIANT/PICKUP_GIANT, no need to repeat this
  around the call.
  
  Approved by:	re (kensmith)

Modified:
  stable/7/sys/   (props changed)
  stable/7/sys/contrib/pf/   (props changed)
  stable/7/sys/dev/cxgb/   (props changed)
  stable/7/sys/kern/kern_sysctl.c

Modified: stable/7/sys/kern/kern_sysctl.c
==============================================================================
--- stable/7/sys/kern/kern_sysctl.c	Fri Dec 19 15:04:26 2008	(r186323)
+++ stable/7/sys/kern/kern_sysctl.c	Fri Dec 19 15:24:18 2008	(r186324)
@@ -52,6 +52,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/mutex.h>
 #include <sys/sx.h>
 #include <sys/sysproto.h>
+#include <sys/uio.h>
 
 #include <security/mac/mac_framework.h>
 
@@ -1395,11 +1396,14 @@ userland_sysctl(struct thread *td, int *
 
 	SYSCTL_LOCK();
 
-	do {
+	for (;;) {
 		req.oldidx = 0;
 		req.newidx = 0;
 		error = sysctl_root(0, name, namelen, &req);
-	} while (error == EAGAIN);
+		if (error != EAGAIN)
+			break;
+		uio_yield();
+	}
 
 	if (req.lock == REQ_WIRED && req.validlen > 0)
 		vsunlock(req.oldptr, req.validlen);

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