[Bug libc/5458] New: PI Mutex Fix breaks multiple program condition variables

[Bug libc/5458] New: PI Mutex Fix breaks multiple program condition variables

[john dot klug at unisys dot com]

A change was introduced to NPTL on 2006-07-29 04:31:49 by
drepper@sourceware.org.  This is in 2.5.

Prior to this change it was possible to use pthread_cond_broadcast() to wake up
a program thread asleep on pthread_cond_wait() using shared memory.

This change is documented in 
http://sourceware.org/cgi-bin/cvsweb.cgi/libc/nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_broadcast.S.diff?cvsroot=glibc&r1=1.9&r2=1.10
&
http://sourceware.org/ml/glibc-cvs/2006-q3/msg00061.html

RCS file:
/cvs/glibc/libc/nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_broadcast.S,v
retrieving revision 1.9
retrieving revision 1.10
diff -u -r1.9 -r1.10

The following instruction dereferences the pointer to the mutex that was
provided by the user in pthread_cond_wait(&cond, &mutex).  This causes a memory
fault if pthread_cond_broadcast(&cond) is not called from the same program as
pthread_cond_signal(), since the address is used out of context.

/cvs/glibc/libc/nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_broadcast.S

+	testl	$PI_BIT, MUTEX_KIND(%r8)

-- 
           Summary: PI Mutex Fix breaks multiple program condition variables
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: critical
          Priority: P2
         Component: libc
        AssignedTo: drepper at redhat dot com
        ReportedBy: john dot klug at unisys dot com
                CC: glibc-bugs at sources dot redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=5458

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[Bug libc/5458] PI Mutex Fix breaks multiple program condition variables

[jakub at redhat dot com]

------- Additional Comments From jakub at redhat dot com  2007-12-07 22:26 -------
If this fails, then you just have a buggy program.
Because this is only tested after testing for pshared condvars:
      /* Do not use requeue for pshared condvars.  */
      if (cond->__data.__mutex == (void *) ~0l)
        goto wake_all;
is in C code, the assembly is equivalent (see comparison to -1 and jump).
You must not use a process private condvar between multiple processes,
you need
pthread_condattr_init/pthread_condattr_setpshared/pthread_condattr_destroy to
make the condvar created as process shared.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


http://sourceware.org/bugzilla/show_bug.cgi?id=5458

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