Bug 671 - It appears syslog can go into deadlock when it receives a signal where the signal handler also syslogs
Summary: It appears syslog can go into deadlock when it receives a signal where the si...
Status: RESOLVED FIXED
Alias: None
Product: glibc
Classification: Unclassified
Component: libc (show other bugs)
Version: 2.3.4
: P2 normal
Target Milestone: ---
Assignee: Roland McGrath
URL:
Keywords:
Depends on:
Blocks: libc235
  Show dependency treegraph
 
Reported: 2005-01-16 01:44 UTC by Brett Lomas
Modified: 2019-04-10 09:18 UTC (History)
1 user (show)

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Host:
Target:
Build:
Last reconfirmed:
fweimer: security-


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Description Brett Lomas 2005-01-16 01:44:02 UTC
I had a program which seemed unresponsive. So I attached GDB to it and got the
following stack strace:
#0  0x00a7e579 in __lll_mutex_lock_wait () from /lib/tls/libc.so.6
#1  0x00a6d955 in _L_mutex_lock_328 () from /lib/tls/libc.so.6
#2  0x093979f8 in ?? ()
#3  0x0805322f in _IO_stdin_used ()
#4  0xbfff90cc in ?? ()
#5  0xbfff9064 in ?? ()
#6  0x00ac79a0 in map () from /lib/tls/libc.so.6
#7  0x00000000 in ?? ()
#8  0x00000000 in ?? ()
#9  0x00000000 in ?? ()
#10 0xbfff8f04 in ?? ()
#11 0x00000000 in ?? ()
#12 0x00000000 in ?? ()
#13 0x0000006e in ?? ()
#14 0x00000014 in ?? ()
#15 0x00000001 in ?? ()
#16 0x09397c88 in ?? ()
#17 0x00000000 in ?? ()
#18 0x41e9970f in ?? ()
#19 0x09397c88 in ?? ()
#20 0x0000003d in ?? ()
#21 0x00a6d8f0 in sigpipe_handler () from /lib/tls/libc.so.6
#22 0x00a6ceef in syslog () from /lib/tls/libc.so.6
#23 0x0804d519 in pusherchld (sig=17) at pusher.c:212
#24 <signal handler called>
#25 0x00a71e8a in send () from /lib/tls/libc.so.6
#26 0x00a6d2a2 in vsyslog () from /lib/tls/libc.so.6
#27 0x00a6ceef in syslog () from /lib/tls/libc.so.6
#28 0x0804d8ef in pusherparent (ppipe=5, gconf=0x9395890) at pusher.c:355
#29 0x0804a821 in main (ac=1024, av=0x1) at daemon.c:465


It appears that while syslog was attempting to send it got a SIGCHLD signal,
which also syslogs.

I have a trivial program (below) which reproduces the problem more often than
not with the follow stack trace:
#0  0x0042be09 in __lll_mutex_lock_wait () from /lib/tls/libc.so.6
#1  0x0041b1b5 in _L_mutex_lock_328 () from /lib/tls/libc.so.6
#2  0x09eaa008 in ?? ()
#3  0x08048808 in _IO_stdin_used ()
#4  0xbfffb258 in ?? ()
#5  0xbfffb1f4 in ?? ()
#6  0x004743a0 in map () from /lib/tls/libc.so.6
#7  0x00000000 in ?? ()


The program is:
#include <stdio.h>
#include <syslog.h>
#include <stdlib.h>
#include <signal.h>
 
 
void
sigchldHandler(int sig)
{
        syslog(LOG_INFO,"Child %d died!!\n",getpid());
}
 
#define SLEEP_MAX 20.0
void
child()
{
        int usecsleep;
        srand(time(NULL)+getpid());
         
        usecsleep=1+(int) (SLEEP_MAX*rand()/(RAND_MAX+1.0));
 
        usleep(usecsleep);
}
 
#define CHILDREN 50
#define NUM_SYSLOGS 1000
 
int
main(int argc,char **argv)
{
        pid_t pids[CHILDREN];
        int i;
 
        signal(SIGCHLD,sigchldHandler);
 
        for(i=0;i<CHILDREN;i++)
        {
                switch((pids[i]=fork()))
                {
                        case 0:
                                child();
                                exit(0);
                        case -1:
                                fprintf(stderr,"Failed fork\n");
                                exit(1);
                }
        }
 
        for(i=0;i<NUM_SYSLOGS;i++)
                syslog(LOG_INFO,"parent: hello!");
 
        for(i=0;i<CHILDREN;i++)
                waitpid(pids[i],NULL,0);
 
        return 0;
}

Thanks
Comment 1 Roland McGrath 2005-02-16 04:08:37 UTC
This problem is avoided by changes already in the trunk CVS, though not yet in
the 2.3 branch.
Comment 2 cvs-commit@gcc.gnu.org 2005-02-16 11:00:25 UTC
Subject: Bug 671

CVSROOT:	/cvs/glibc
Module name:	libc
Branch: 	glibc-2_3-branch
Changes by:	roland@sources.redhat.com	2005-02-16 11:00:09

Added files:
	sysdeps/generic: syslog.c 

Log message:
	2005-02-02  Alfred M. Szmidt  <ams@gnu.org>
	
	[BZ #671]
	* sysdeps/generic/syslog.c (send_flags) [!send_flags]: Define it.
	2005-01-25  Roland McGrath  <roland@redhat.com>
	
	[BZ #671]
	* sysdeps/generic/syslog.c [NO_SIGPIPE]: Protect sigpipe_handler decl.
	2005-01-24  Ulrich Drepper  <drepper@redhat.com>
	
	[BZ #671]
	* misc/syslog.c: Moved to...
	* sysdeps/generic/syslog.c: ...here.
	[NO_SIGIPE]: Don't install SIGPIPE handler.
	* sysdeps/unix/sysv/linux/syslog.c: New file.
	* sysdeps/unix/sysv/linux/kernel-features.h: Define
	__ASSUME_MSG_NOSIGNAL.

Patches:
http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/sysdeps/generic/syslog.c.diff?cvsroot=glibc&only_with_tag=glibc-2_3-branch&r1=NONE&r2=1.3.4.1

Comment 3 cvs-commit@gcc.gnu.org 2005-02-16 11:00:37 UTC
Subject: Bug 671

CVSROOT:	/cvs/glibc
Module name:	libc
Branch: 	glibc-2_3-branch
Changes by:	roland@sources.redhat.com	2005-02-16 11:00:16

Added files:
	sysdeps/unix/sysv/linux: syslog.c 
Removed files:
	misc           : syslog.c 

Log message:
	2005-01-24  Ulrich Drepper  <drepper@redhat.com>
	
	[BZ #671]
	* misc/syslog.c: Moved to...
	* sysdeps/generic/syslog.c: ...here.
	[NO_SIGIPE]: Don't install SIGPIPE handler.
	* sysdeps/unix/sysv/linux/syslog.c: New file.
	* sysdeps/unix/sysv/linux/kernel-features.h: Define
	__ASSUME_MSG_NOSIGNAL.

Patches:
http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/misc/syslog.c.diff?cvsroot=glibc&only_with_tag=glibc-2_3-branch&r1=1.44&r2=NONE
http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/sysdeps/unix/sysv/linux/syslog.c.diff?cvsroot=glibc&only_with_tag=glibc-2_3-branch&r1=NONE&r2=1.1.4.1

Comment 4 cvs-commit@gcc.gnu.org 2005-02-16 11:00:39 UTC
Subject: Bug 671

CVSROOT:	/cvs/glibc
Module name:	libc
Branch: 	glibc-2_3-branch
Changes by:	roland@sources.redhat.com	2005-02-16 11:00:22

Modified files:
	sysdeps/unix/sysv/linux: kernel-features.h 

Log message:
	2005-01-26  Ulrich Drepper  <drepper@redhat.com>
	
	[BZ #671]
	* sysdeps/unix/sysv/linux/kernel-features.h: Found reference to
	MSG_NOSIGNAL being in 2.2 kernels.
	2005-01-24  Ulrich Drepper  <drepper@redhat.com>
	
	[BZ #671]
	* misc/syslog.c: Moved to...
	* sysdeps/generic/syslog.c: ...here.
	[NO_SIGIPE]: Don't install SIGPIPE handler.
	* sysdeps/unix/sysv/linux/syslog.c: New file.
	* sysdeps/unix/sysv/linux/kernel-features.h: Define
	__ASSUME_MSG_NOSIGNAL.

Patches:
http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/sysdeps/unix/sysv/linux/kernel-features.h.diff?cvsroot=glibc&only_with_tag=glibc-2_3-branch&r1=1.81&r2=1.81.2.1

Comment 5 Roland McGrath 2005-04-05 23:59:34 UTC
These changes are in the 2.3 branch as well as the trunk now.