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Date: Fri, 27 Oct 2006 08:32:00 -0000
From: Jakub Jelinek <jakub@redhat.com>
To: Ulrich Drepper <drepper@redhat.com>
Cc: Glibc hackers <libc-hacker@sources.redhat.com>
Subject: [PATCH] Fix __rtld_mrlock_{lock,change}
Message-ID: <20061027083211.GP5868@sunsite.mff.cuni.cz>
Reply-To: Jakub Jelinek <jakub@redhat.com>
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X-SW-Source: 2006-10/txt/msg00018.txt.bz2

Hi!

__rtld_mrlock_{lock,change} can get into an endless loop.  If lock is
changed between oldval = lock and the atomic compare and swap, the loop
will cycle until something changes lock back to the oldvalue (which doesn't
have to happen ever).  When CAS is unsuccessful, we need to reread oldval,
either from lock directly or better yet from what CAS returned.

2006-10-27  Jakub Jelinek  <jakub@redhat.com>

	* sysdeps/unix/sysv/linux/rtld-lowlevel.h (__rtld_mrlock_lock,
	__rtld_mrlock_change): Update oldval if atomic compare and exchange
	failed.

--- libc/nptl/sysdeps/unix/sysv/linux/rtld-lowlevel.h.jj	2006-10-19 17:26:40.000000000 +0200
+++ libc/nptl/sysdeps/unix/sysv/linux/rtld-lowlevel.h	2006-10-25 21:36:37.000000000 +0200
@@ -67,6 +67,7 @@ typedef int __rtld_mrlock_t;
 							       oldval);	      \
 		if (__builtin_expect (ret == oldval, 1))		      \
 		  goto out;						      \
+		oldval = ret;						      \
 	      }								      \
 	    atomic_delay ();						      \
 	  }								      \
@@ -112,6 +113,7 @@ typedef int __rtld_mrlock_t;
 							       oldval);	      \
 		if (__builtin_expect (ret == oldval, 1))		      \
 		  goto out;						      \
+		oldval = ret;						      \
 	      }								      \
 	    atomic_delay ();						      \
 	  }								      \

	Jakub