linux-kernel - Re: [PATCH net-next v3 04/11] selftests/vsock: avoid multi-VM pidfile collisions with QEMU

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Message-ID: <aQ4RrcB0tzMWch1S@devvm11784.nha0.facebook.com>
Date: Fri, 7 Nov 2025 07:35:09 -0800
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: Simon Horman <horms@...nel.org>
Cc: Stefano Garzarella <sgarzare@...hat.com>, Shuah Khan <shuah@...nel.org>,
	virtualization@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bobby Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next v3 04/11] selftests/vsock: avoid multi-VM
 pidfile collisions with QEMU

On Fri, Nov 07, 2025 at 03:08:25PM +0000, Simon Horman wrote:
> On Thu, Nov 06, 2025 at 04:49:48PM -0800, Bobby Eshleman wrote:
> 
> ...
> 
> > @@ -90,15 +85,19 @@ vm_ssh() {
> >  }
> >  
> >  cleanup() {
> > -	if [[ -s "${QEMU_PIDFILE}" ]]; then
> > -		pkill -SIGTERM -F "${QEMU_PIDFILE}" > /dev/null 2>&1
> > -	fi
> > +	local pidfile
> >  
> > -	# If failure occurred during or before qemu start up, then we need
> > -	# to clean this up ourselves.
> > -	if [[ -e "${QEMU_PIDFILE}" ]]; then
> > -		rm "${QEMU_PIDFILE}"
> > -	fi
> > +	for pidfile in "${PIDFILES[@]}"; do
> > +		if [[ -s "${pidfile}" ]]; then
> > +			pkill -SIGTERM -F "${pidfile}" > /dev/null 2>&1
> > +		fi
> > +
> > +		# If failure occurred during or before qemu start up, then we need
> > +		# to clean this up ourselves.
> > +		if [[ -e "${pidfile}" ]]; then
> > +			rm "${pidfile}"
> > +		fi
> > +	done
> >  }
> 
> Hi Bobby,
> 
> This is completely untested, but it looks to me
> like cleanup() could be implemented more succinctly like this.
> 
> cleanup() {
> 	terminate_pidfiles "${PIDFILES[@]}"
> }
> 

Oh right! I reverted the deletion and completely forgot about
terminate_pidfiles().

> >  
> >  check_args() {
> > @@ -188,10 +187,35 @@ handle_build() {
> >  	popd &>/dev/null
> >  }
> >  
> > +create_pidfile() {
> > +	local pidfile
> > +
> > +	pidfile=$(mktemp "${PIDFILE_TEMPLATE}")
> > +	PIDFILES+=("${pidfile}")
> > +
> > +	echo "${pidfile}"
> > +}
> > +
> > +terminate_pidfiles() {
> > +	local pidfile
> > +
> > +	for pidfile in "$@"; do
> > +		if [[ -s "${pidfile}" ]]; then
> > +			pkill -SIGTERM -F "${pidfile}" > /dev/null 2>&1
> > +		fi
> > +
> > +		if [[ -e "${pidfile}" ]]; then
> > +			rm -f "${pidfile}"
> > +		fi
> > +	done
> 
> I think it would be useful to remove $pidfile from $PIDFILES.
> This might be easier to implement if PIDFILES was an associative array.
> 

Using an associative makes sense, this way we can trim the set.

> > +}
> > +
> 
> ...
> 
> > @@ -498,7 +529,8 @@ handle_build
> >  echo "1..${#ARGS[@]}"
> >  
> >  log_host "Booting up VM"
> > -vm_start
> > +pidfile="$(create_pidfile)"
> > +vm_start "${pidfile}"
> >  vm_wait_for_ssh
> >  log_host "VM booted up"
> >  
> 
> > @@ -522,6 +554,8 @@ for arg in "${ARGS[@]}"; do
> >  	cnt_total=$(( cnt_total + 1 ))
> >  done
> >  
> > +terminate_pidfiles "${pidfile}"
> 
> I am assuming that there will be more calls to terminate_pidfiles
> in subsequent patch-sets.
> 
> Else I think terminate_pidfiles can be removed
> and instead we can rely on cleanup().
> 

Indeed, later patches will use terminate_pidfiles() in between spin up /
shut down of multiple VMs.


Thanks again, will incorporate your feedback in the next!

Best,
Bobby