[Bug nptl/9804] New: pthread_exit from main thread: poor semantics, potential tty session lockup.

["kkylheku at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

(I'm using glibc 2.9; the Version field only goes up to 2.8. The following 
behavior occurs as far back as 2.5).

The kernel is 2.6.26. I'm running i686 and mips; it doesn't matter. I have not 
tried a newer kernel than this.

The issue is that if the main thread of a process terminates with 
pthread_exit, while other threads are still running, the kernel task 
associated with the main thread becomes defunct in some kind of sleep that 
cannot be interrupted by an ordinary signal. As such, the kernel will not 
allow job control to be performed on that process. The process cannot be 
suspended with Ctrl-Z from the shell, nor can it be killed with Ctrl-C.

Moreover, attempts to manipulate it in these ways can cause it to permanently 
hang in that sleep, and no longer terminate even when the other threads do. In 
that situation, the user cannot regain control over the tty session, except by 
logging in via another terminal and killing the defunct process with the 
SIGKILL signal.

The expected behavior is that the process should continue to exist as a normal 
process as long as at least one thread remains running. Normal POSIX job 
control should be possible over that process: switching its process group from 
the foreground to the background, killing it with Ctrl-C.

This may require either a kernel patch, or a change in glibc so that 
pthread_exit from the main thread does not in fact perform a task exit at the 
OS level, but merely a user-space synchronization on the other threads.

(I will explore this from a kernel angle and add any findings or patches here, 
using glibc 2.9 on 2.6.26 as my reference base).

-- 
           Summary: pthread_exit from main thread: poor semantics, potential
                    tty session lockup.
           Product: glibc
           Version: 2.8
            Status: NEW
          Severity: normal
          Priority: P2
         Component: nptl
        AssignedTo: drepper at redhat dot com
        ReportedBy: kkylheku at gmail dot com
                CC: glibc-bugs at sources dot redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=9804

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