| Message ID | 1470134368-13799-3-git-send-email-jgross@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Aug 02, 2016 at 12:39:26PM +0200, Juergen Gross wrote: > In order to prepare starting a xenstore domain split out the starting > of the xenstore daemon from the xencommons script into a dedicated > launch-xenstore script. > > Correct one error: don't remove old tdb files in background, as this > could lead to very subtle races. > Sorry to only notice this now -- I suppose this shouldn't be in commit message because it is a changelog for different revision of your patch, or you need to describe what the race is if there is really such issue -- and that's a potential backport candidate. As far as I can tell this is pure code motion and shouldn't have any change in behaviour. Hence this line in commit message makes me feel a bit confused. Wei.
On 02/08/16 13:13, Wei Liu wrote: > On Tue, Aug 02, 2016 at 12:39:26PM +0200, Juergen Gross wrote: >> In order to prepare starting a xenstore domain split out the starting >> of the xenstore daemon from the xencommons script into a dedicated >> launch-xenstore script. >> >> Correct one error: don't remove old tdb files in background, as this >> could lead to very subtle races. >> > > Sorry to only notice this now -- I suppose this shouldn't be in commit > message because it is a changelog for different revision of your patch, > or you need to describe what the race is if there is really such issue > -- and that's a potential backport candidate. - rm -f "$XENSTORED_ROOTDIR"/tdb* &>/dev/null ... + rm -f "$XENSTORED_ROOTDIR"/tdb* 2>/dev/null Please note the "&" in the removed line. And the description just tells you that: the file shouldn't be removed in the background. How else would you describe it? And the race should be obvious: removing a file in the background which is going to be used by the next command is racy. > As far as I can tell this is pure code motion and shouldn't have any > change in behaviour. Hence this line in commit message makes me feel a > bit confused. Still confused? Juergen
On Tue, Aug 02, 2016 at 01:20:40PM +0200, Juergen Gross wrote: > On 02/08/16 13:13, Wei Liu wrote: > > On Tue, Aug 02, 2016 at 12:39:26PM +0200, Juergen Gross wrote: > >> In order to prepare starting a xenstore domain split out the starting > >> of the xenstore daemon from the xencommons script into a dedicated > >> launch-xenstore script. > >> > >> Correct one error: don't remove old tdb files in background, as this > >> could lead to very subtle races. > >> > > > > Sorry to only notice this now -- I suppose this shouldn't be in commit > > message because it is a changelog for different revision of your patch, > > or you need to describe what the race is if there is really such issue > > -- and that's a potential backport candidate. > > - rm -f "$XENSTORED_ROOTDIR"/tdb* &>/dev/null > ... > + rm -f "$XENSTORED_ROOTDIR"/tdb* 2>/dev/null > > Please note the "&" in the removed line. And the description just tells > you that: the file shouldn't be removed in the background. How else > would you describe it? > > And the race should be obvious: removing a file in the background which > is going to be used by the next command is racy. > > > As far as I can tell this is pure code motion and shouldn't have any > > change in behaviour. Hence this line in commit message makes me feel a > > bit confused. > > Still confused? Ah, the 2> vs &> thing is really subtle. I missed that, sorry. I think you need to separate that one change out so that we can backport it to stable releases to avoid the race. Wei. > > > Juergen
On Tue, Aug 02, Juergen Gross wrote: > - rm -f "$XENSTORED_ROOTDIR"/tdb* &>/dev/null > + rm -f "$XENSTORED_ROOTDIR"/tdb* 2>/dev/null > > Please note the "&" in the removed line. And the description just tells > you that: the file shouldn't be removed in the background. How else > would you describe it? "&>" redirects stdout and stderr at the same time. See bash(1) "Redirecting Standard Output and Standard Error". Are you saying it does fork into background instead? Olaf
On 02/08/16 13:59, Olaf Hering wrote: > On Tue, Aug 02, Juergen Gross wrote: > >> - rm -f "$XENSTORED_ROOTDIR"/tdb* &>/dev/null >> + rm -f "$XENSTORED_ROOTDIR"/tdb* 2>/dev/null >> >> Please note the "&" in the removed line. And the description just tells >> you that: the file shouldn't be removed in the background. How else >> would you describe it? > > "&>" redirects stdout and stderr at the same time. See bash(1) > "Redirecting Standard Output and Standard Error". > Are you saying it does fork into background instead? No. I'm saying that I managed to overlook that part of the man page. I explicitly had a look as I didn't know the &> notation and I wanted to make sure I don't miss anything. I failed obviously. :-( Thanks for the bash lesson. :-) V5 is about to come... Juergen
Wei Liu writes ("Re: [PATCH v4 2/4] tools: split out xenstored starting form xencommons"):
> On Tue, Aug 02, 2016 at 01:20:40PM +0200, Juergen Gross wrote:
> > Still confused?
>
> Ah, the 2> vs &> thing is really subtle. I missed that, sorry.
`&>' is a (bash-specific, I think) syntax for redirection, not a
request to run anything in the background.
Ian.
Olaf Hering writes ("Re: [Xen-devel] [PATCH v4 2/4] tools: split out xenstored starting form xencommons"):
> "&>" redirects stdout and stderr at the same time. See bash(1)
> "Redirecting Standard Output and Standard Error".
> Are you saying it does fork into background instead?
Snap. That'll teach me not to read the whole thread :-).
Ian.
On Tue, Aug 02, 2016 at 02:48:54PM +0100, Ian Jackson wrote: > Wei Liu writes ("Re: [PATCH v4 2/4] tools: split out xenstored starting form xencommons"): > > On Tue, Aug 02, 2016 at 01:20:40PM +0200, Juergen Gross wrote: > > > Still confused? > > > > Ah, the 2> vs &> thing is really subtle. I missed that, sorry. > > `&>' is a (bash-specific, I think) syntax for redirection, not a > request to run anything in the background. > I skimmed too fast and read that as "& >". :-/ > Ian.
diff --git a/.gitignore b/.gitignore index 9b8dece..d193820 100644 --- a/.gitignore +++ b/.gitignore @@ -157,6 +157,7 @@ tools/hotplug/Linux/init.d/xen-watchdog tools/hotplug/Linux/init.d/xencommons tools/hotplug/Linux/init.d/xendomains tools/hotplug/Linux/init.d/xendriverdomain +tools/hotplug/Linux/launch-xenstore tools/hotplug/Linux/systemd/*.conf tools/hotplug/Linux/systemd/*.mount tools/hotplug/Linux/systemd/*.socket diff --git a/tools/configure b/tools/configure index 1c84c6c..51f16c5 100755 --- a/tools/configure +++ b/tools/configure @@ -2410,7 +2410,7 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu -ac_config_files="$ac_config_files ../config/Tools.mk hotplug/FreeBSD/rc.d/xencommons hotplug/FreeBSD/rc.d/xendriverdomain hotplug/Linux/init.d/sysconfig.xencommons hotplug/Linux/init.d/sysconfig.xendomains hotplug/Linux/init.d/xen-watchdog hotplug/Linux/init.d/xencommons hotplug/Linux/init.d/xendomains hotplug/Linux/init.d/xendriverdomain hotplug/Linux/vif-setup hotplug/Linux/xen-hotplug-common.sh hotplug/Linux/xendomains hotplug/NetBSD/rc.d/xencommons hotplug/NetBSD/rc.d/xendriverdomain libxl/xenlight.pc.in libxl/xlutil.pc.in ocaml/xenstored/oxenstored.conf" +ac_config_files="$ac_config_files ../config/Tools.mk hotplug/FreeBSD/rc.d/xencommons hotplug/FreeBSD/rc.d/xendriverdomain hotplug/Linux/init.d/sysconfig.xencommons hotplug/Linux/init.d/sysconfig.xendomains hotplug/Linux/init.d/xen-watchdog hotplug/Linux/init.d/xencommons hotplug/Linux/init.d/xendomains hotplug/Linux/init.d/xendriverdomain hotplug/Linux/launch-xenstore hotplug/Linux/vif-setup hotplug/Linux/xen-hotplug-common.sh hotplug/Linux/xendomains hotplug/NetBSD/rc.d/xencommons hotplug/NetBSD/rc.d/xendriverdomain libxl/xenlight.pc.in libxl/xlutil.pc.in ocaml/xenstored/oxenstored.conf" ac_config_headers="$ac_config_headers config.h" @@ -10376,6 +10376,7 @@ do "hotplug/Linux/init.d/xencommons") CONFIG_FILES="$CONFIG_FILES hotplug/Linux/init.d/xencommons" ;; "hotplug/Linux/init.d/xendomains") CONFIG_FILES="$CONFIG_FILES hotplug/Linux/init.d/xendomains" ;; "hotplug/Linux/init.d/xendriverdomain") CONFIG_FILES="$CONFIG_FILES hotplug/Linux/init.d/xendriverdomain" ;; + "hotplug/Linux/launch-xenstore") CONFIG_FILES="$CONFIG_FILES hotplug/Linux/launch-xenstore" ;; "hotplug/Linux/vif-setup") CONFIG_FILES="$CONFIG_FILES hotplug/Linux/vif-setup" ;; "hotplug/Linux/xen-hotplug-common.sh") CONFIG_FILES="$CONFIG_FILES hotplug/Linux/xen-hotplug-common.sh" ;; "hotplug/Linux/xendomains") CONFIG_FILES="$CONFIG_FILES hotplug/Linux/xendomains" ;; diff --git a/tools/configure.ac b/tools/configure.ac index f991ab3..3a4abb5 100644 --- a/tools/configure.ac +++ b/tools/configure.ac @@ -15,6 +15,7 @@ hotplug/Linux/init.d/xen-watchdog hotplug/Linux/init.d/xencommons hotplug/Linux/init.d/xendomains hotplug/Linux/init.d/xendriverdomain +hotplug/Linux/launch-xenstore hotplug/Linux/vif-setup hotplug/Linux/xen-hotplug-common.sh hotplug/Linux/xendomains diff --git a/tools/hotplug/Linux/Makefile b/tools/hotplug/Linux/Makefile index 6d6ccee..29280cb 100644 --- a/tools/hotplug/Linux/Makefile +++ b/tools/hotplug/Linux/Makefile @@ -30,6 +30,7 @@ XEN_SCRIPTS += block-drbd-probe XEN_SCRIPTS += block-dummy XEN_SCRIPTS += $(XEN_SCRIPTS-y) XEN_SCRIPTS += colo-proxy-setup +XEN_SCRIPTS += launch-xenstore SUBDIRS-$(CONFIG_SYSTEMD) += systemd diff --git a/tools/hotplug/Linux/init.d/xencommons.in b/tools/hotplug/Linux/init.d/xencommons.in index 2d8f30b..a32608c 100644 --- a/tools/hotplug/Linux/init.d/xencommons.in +++ b/tools/hotplug/Linux/init.d/xencommons.in @@ -18,7 +18,6 @@ # Description: Starts and stops the daemons neeeded for xl/xend ### END INIT INFO -XENSTORED=@XENSTORED@ BACKEND_MODULES="@LINUX_BACKEND_MODULES@" . @XEN_SCRIPT_DIR@/hotplugpath.sh @@ -53,8 +52,6 @@ if test -f /proc/xen/capabilities && \ fi do_start () { - local time=0 - local timeout=30 local mod for mod in $BACKEND_MODULES ; do modprobe "$mod" &>/dev/null ; done @@ -62,37 +59,10 @@ do_start () { mkdir -p ${XEN_RUN_DIR} mkdir -p ${XEN_LOCK_DIR} - if ! `${bindir}/xenstore-read -s / >/dev/null 2>&1` - then - test -z "$XENSTORED_ROOTDIR" && XENSTORED_ROOTDIR="@XEN_LIB_STORED@" - rm -f "$XENSTORED_ROOTDIR"/tdb* &>/dev/null - test -z "$XENSTORED_TRACE" || XENSTORED_ARGS=" -T @XEN_LOG_DIR@/xenstored-trace.log" + @XEN_SCRIPT_DIR@/launch-xenstore || exit 1 - if [ -n "$XENSTORED" ] ; then - echo -n Starting $XENSTORED... - $XENSTORED --pid-file @XEN_RUN_DIR@/xenstored.pid $XENSTORED_ARGS - else - echo "No xenstored found" - exit 1 - fi - - # Wait for xenstored to actually come up, timing out after 30 seconds - while [ $time -lt $timeout ] && ! `${bindir}/xenstore-read -s / >/dev/null 2>&1` ; do - echo -n . - time=$(($time+1)) - sleep 1 - done - echo - - # Exit if we timed out - if ! [ $time -lt $timeout ] ; then - echo Could not start xenstored - exit 1 - fi - - echo Setting domain 0 name, domid and JSON config... - ${LIBEXEC_BIN}/xen-init-dom0 - fi + echo Setting domain 0 name, domid and JSON config... + ${LIBEXEC_BIN}/xen-init-dom0 echo Starting xenconsoled... test -z "$XENCONSOLED_TRACE" || XENCONSOLED_ARGS=" --log=$XENCONSOLED_TRACE" diff --git a/tools/hotplug/Linux/launch-xenstore.in b/tools/hotplug/Linux/launch-xenstore.in new file mode 100644 index 0000000..a0cbfd3 --- /dev/null +++ b/tools/hotplug/Linux/launch-xenstore.in @@ -0,0 +1,55 @@ +#!/bin/bash +# +# Copyright (c) 2016 SUSE Linux GmbH +# +# This library is free software; you can redistribute it and/or +# modify it under the terms of version 2.1 of the GNU Lesser General Public +# License as published by the Free Software Foundation. +# +# This library is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +# Lesser General Public License for more details. +# +# You should have received a copy of the GNU Lesser General Public +# License along with this library; If not, see <http://www.gnu.org/licenses/>. +# + +XENSTORED=@XENSTORED@ + +. @XEN_SCRIPT_DIR@/hotplugpath.sh +test -f @CONFIG_DIR@/@CONFIG_LEAF_DIR@/xencommons && . @CONFIG_DIR@/@CONFIG_LEAF_DIR@/xencommons + +time=0 +timeout=30 + +if ! `${bindir}/xenstore-read -s / >/dev/null 2>&1` +then + test -z "$XENSTORED_ROOTDIR" && XENSTORED_ROOTDIR="@XEN_LIB_STORED@" + rm -f "$XENSTORED_ROOTDIR"/tdb* 2>/dev/null + test -z "$XENSTORED_TRACE" || XENSTORED_ARGS=" -T @XEN_LOG_DIR@/xenstored-trace.log" + + if [ -n "$XENSTORED" ] ; then + echo -n Starting $XENSTORED... + $XENSTORED --pid-file @XEN_RUN_DIR@/xenstored.pid $XENSTORED_ARGS + else + echo "No xenstored found" + exit 1 + fi + + # Wait for xenstored to actually come up, timing out after 30 seconds + while [ $time -lt $timeout ] && ! `${bindir}/xenstore-read -s / >/dev/null 2>&1` ; do + echo -n . + time=$(($time+1)) + sleep 1 + done + echo + + # Exit if we timed out + if ! [ $time -lt $timeout ] ; then + echo Could not start xenstored + exit 1 + fi +fi + +exit 0
In order to prepare starting a xenstore domain split out the starting of the xenstore daemon from the xencommons script into a dedicated launch-xenstore script. Correct one error: don't remove old tdb files in background, as this could lead to very subtle races. A rerun of autogen.sh is required. Signed-off-by: Juergen Gross <jgross@suse.com> --- .gitignore | 1 + tools/configure | 3 +- tools/configure.ac | 1 + tools/hotplug/Linux/Makefile | 1 + tools/hotplug/Linux/init.d/xencommons.in | 36 ++------------------- tools/hotplug/Linux/launch-xenstore.in | 55 ++++++++++++++++++++++++++++++++ 6 files changed, 63 insertions(+), 34 deletions(-) create mode 100644 tools/hotplug/Linux/launch-xenstore.in