[kexec-tools/f19] kdumpctl: Run multiple kdumpctl instances one by one in serial order

[Baoquan He]

commit 23e078ffdbdfd45bbd653c69399e61c5f000872b
Author: WANG Chao <chaowang at redhat.com>
Date:   Fri Aug 30 17:21:56 2013 +0800

    kdumpctl: Run multiple kdumpctl instances one by one in serial order
    
    There will be a race condition if multiple kdumpctl instances are
    running at the same time.
    
    By introducing a global mutex lock, only one instance can acquire this
    lock and run, others will be waiting for the lock in queue. Now each
    kdump instance will be run in serial order and there won't any race
    condition.
    
    This is a patch backported from RHEL6.
    
    Signed-off-by: WANG Chao <chaowang at redhat.com>
    Acked-by: Vivek Goyal <vgoyal at redhat.com>
    Acked-by: Dave Young <dyoung at redhat.com>

 kdumpctl |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)
---
diff --git a/kdumpctl b/kdumpctl
index aba1e3c..d62b4b4 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -16,6 +16,12 @@ if [ -f /etc/sysconfig/kdump ]; then
 	. /etc/sysconfig/kdump
 fi
 
+single_instance_lock()
+{
+	exec 9>/var/lock/kdump
+	flock 9
+}
+
 # remove_cmdline_param <kernel cmdline> <param1> [<param2>] ... [<paramN>]
 # Remove a list of kernel parameters from a given kernel cmdline and print the result.
 # For each "arg" in the removing params list, "arg" and "arg=xxx" will be removed if exists.
@@ -531,6 +537,9 @@ if [ ! -f "$KDUMP_CONFIG_FILE" ]; then
 	exit 1
 fi
 
+# Other kdumpctl instances will block in queue, until this one exits
+single_instance_lock
+
 case "$1" in
   start)
 	if [ -s /proc/vmcore ]; then