[libvirt] [PATCH] util: ignore SIGPIPE when writing tostderr/stdout

[Daniel P. Berrangé]

On Mon, Oct 14, 2019 at 06:46:54PM +0800, wang.yechao255 at zte.com.cn wrote:
> > On Sat, Oct 12, 2019 at 16:04:11 +0800, Wang Yechao wrote:
> > > libvirtd's stderr/stdout redirected to journald by default, so if
> > > the journald has stopped, libvirtd and libvirtd's child process
> > > will receive SIGPIPE signal when writing logs to stderr/stdout.
> > >
> > > journald stopped reasons:
> > > 1. manual command "systemctl stop systemd-journald.service"
> > > 2. oom killer kill it.
> >
> > What is configuration of logging for libvirtd? Libvirtd should not log
> > to stdout by default so I think this is more of a misconfiguration than
> > something needing fix in code.
> >
> In my env, the libvirtd.conf like that:
> "
> log_level = 1
> log_outputs="2:file:/var/log/libvirt/libvirtd.log"
> "
> 
> Libvirtd works fine in this configuration, if i stop the journald.serivce.
> But the child process that forked by libvirtd, will face this problem:
> 
> # virsh create vm.xml
> error: Failed to create domain from vm.xml
> error: internal error: Child process (LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin /usr/libexec/qemu-kvm -S -no-user-config -nodefaults -nographic -machine none,accel=kvm:tcg -qmp unix:/usr/local/var/lib/libvirt/qemu/qmp-vtKZqu/qmp.monitor,server,nowait -pidfile /usr/local/var/lib/libvirt/qemu/qmp-vtKZqu/qmp.pid -daemonize) unexpected fatal signal 13
> 
> 
> The version of libvirt that i test:
> # virsh version
> Compiled against library: libvirt 5.9.0
> Using library: libvirt 5.9.0
> Using API: QEMU 5.9.0
> 
> The child process recieve signal SIGPIPE, backtrace as follows:
> Program received signal SIGPIPE, Broken pipe.
> [Switching to Thread 0x7fa44dd25700 (LWP 67788)]
> 0x00007fa45b63779d in write () from /lib64/libpthread.so.0
> (gdb) bt
> #0  0x00007fa45b63779d in write () from /lib64/libpthread.so.0
> #1  0x00007fa45e51f6ae in safewrite (fd=fd at entry=2, buf=buf at entry=0x7fa43800e6e0, count=76) at util/virfile.c:1089
> #2  0x00007fa45e53ba85 in virLogOutputToFd (source=source at entry=0x7fa45ea9b8a0 <virLogSelf>, priority=priority at entry=VIR_LOG_DEBUG,
>     filename=filename at entry=0x7fa45e7829b8 "util/virfile.c", linenr=linenr at entry=114,
>     funcname=funcname at entry=0x7fa45e783d64 <__func__.19089> "virFileClose", timestamp=timestamp at entry=0x7fa44dd23af0 "2019-10-14 09:11:06.087+0000",
>     metadata=metadata at entry=0x0, flags=flags at entry=0, rawstr=0x7fa43800ed20 "Closed fd 3",
>     str=0x7fa4380108d0 "67788: debug : virFileClose:114 : Closed fd 3\n", data=data at entry=0x2) at util/virlog.c:738
> #3  0x00007fa45e53cdae in virLogVMessage (source=0x7fa45ea9b8a0 <virLogSelf>, priority=VIR_LOG_DEBUG, filename=0x7fa45e7829b8 "util/virfile.c",
>     linenr=114, funcname=0x7fa45e783d64 <__func__.19089> "virFileClose", metadata=0x0, fmt=fmt at entry=0x7fa45e782a48 "Closed fd %d",
>     vargs=vargs at entry=0x7fa44dd23b70) at util/virlog.c:682
> #4  0x00007fa45e53cfc7 in virLogMessage (source=source at entry=0x7fa45ea9b8a0 <virLogSelf>, priority=priority at entry=VIR_LOG_DEBUG,
>     filename=filename at entry=0x7fa45e7829b8 "util/virfile.c", linenr=linenr at entry=114,
>     funcname=funcname at entry=0x7fa45e783d64 <__func__.19089> "virFileClose", metadata=metadata at entry=0x0, fmt=fmt at entry=0x7fa45e782a48 "Closed fd %d")
>     at util/virlog.c:556
> #5  0x00007fa45e51ebaa in virFileClose (fdptr=fdptr at entry=0x7fa44dd24148,
>     flags=flags at entry=(VIR_FILE_CLOSE_PRESERVE_ERRNO | VIR_FILE_CLOSE_IGNORE_EBADF)) at util/virfile.c:114
> #6  0x00007fa45e4efae7 in virCommandMassClose (childerr=<optimized out>, childout=33, childin=31, cmd=0x7fa4380119f0) at util/vircommand.c:525
> #7  virExec (cmd=cmd at entry=0x7fa4380119f0) at util/vircommand.c:656

At this point you are int he child QEMU process.

virFork resets all signal handlers back to their default setting so that
libvirtd's choice of signals doesn't impact the child process.

Perhaps the right answer is to use pthread_sigmask to block SIGPIPE
until just before we execve

Regards,
Daniel
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