Bug#410899: libc6: _IO_stdfile_0_lock deadlock in printf cancellation

[Ron <ron@debian.org>]

Package: libc6
Version: 2.3.6.ds1-11
Severity: normal

Hi,

I'm led to believe (from older libc docs that include POSIX threads)
that printf is a known cancellation point (albeit indirectly).

However, in practice it appears that if it is called with a cancellation
request pending it will deadlock...  The following code reproduces this:


#define _REENTRANT 1

#include <pthread.h>
#include <stdio.h>

void *thread(void*)
{
    printf("hello thread\n");
    return NULL;
}

int main()
{
    pthread_t id;
    pthread_create(&id,NULL,thread,NULL);
    pthread_cancel(id);
    printf("joining thread\n");
    pthread_join(id,NULL);
    printf("done\n");

    return 0;
}


$ g++ -g thread_join.cpp -o thread_join -pthread
$ ./thread_join
joining thread
<hang>


$ gdb ./thread_join 18867
(gdb) info threads
  1 Thread 47608883437824 (LWP 18867)  0x00002b4cce7f530b in __lll_mutex_lock_wait () from /lib/libc.so.6
(gdb) bt
#0  0x00002b4cce7f530b in __lll_mutex_lock_wait () from /lib/libc.so.6
#1  0x00002b4cce959090 in _IO_stdfile_0_lock () from /lib/libc.so.6
#2  0x0000000000000000 in ?? ()

Cheers,
Ron


-- System Information:
Debian Release: 4.0
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  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)
Shell:  /bin/sh linked to /bin/bash
Kernel: Linux 2.6.18-4-amd64
Locale: LANG=en_AU.UTF-8, LC_CTYPE=en_AU.UTF-8 (charmap=UTF-8)

Versions of packages libc6 depends on:
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