File kdump-udev-reload-only-once.patch of Package kdump

From: Petr Tesarik <ptesarik@suse.com>
Date: Fri Sep 4 10:16:25 2015 +0200
Subject: Reload kdump only once if multiple udev events happen in parallel
References: bsc#934581
Patch-mainline: v0.8.16
Git-commit: 6859c6c7e8abd0f141ab4709d68d5e50800de80a

The kexec(2) system call is not re-entrant, so kdump reload may fail
if another reload is already in progress. Solve this by serializing
the requests using a lock file under /var/run.

Note that it is sufficient to re-run kexec(1) once after all memory
configuration changes are finished. To avoid unnecessary runs, the
following logic is implemented: If a reload is already in progress,
all subsequent reloads exit immediately, letting the running instance
redo the job. A jobs file is used to tell the running instance that
there are more changes after the first one, so it must reload the
kdump kernel one more time.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>

---
 70-kdump.rules.in   |    2 +-
 init/CMakeLists.txt |    1 +
 init/load-once.sh   |   23 +++++++++++++++++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

--- a/init/CMakeLists.txt
+++ b/init/CMakeLists.txt
@@ -78,6 +78,7 @@ INSTALL(
         ${CMAKE_CURRENT_SOURCE_DIR}/setup-kdump.functions
         ${CMAKE_CURRENT_SOURCE_DIR}/save_dump.sh
         ${CMAKE_CURRENT_SOURCE_DIR}/load.sh
+        ${CMAKE_CURRENT_SOURCE_DIR}/load-once.sh
         ${CMAKE_CURRENT_SOURCE_DIR}/unload.sh
     DESTINATION
         /lib/kdump
--- /dev/null
+++ b/init/load-once.sh
@@ -0,0 +1,23 @@
+#! /bin/bash
+
+# This script ensures that kdump is (re-)loaded once.
+# It prevents multiple invocation of load.sh even if multiple instances
+# of the script are run in parallel. The first instance repeats the action
+# as long as there is any pending work.
+
+LOCKFILE=/var/run/kdump.lock
+JOBSFILE=/var/run/kdump.jobs
+export JOBSFILE
+
+# Add a pending job
+echo $$ >> "$JOBSFILE"
+
+# Make sure lock-file exists
+> "$LOCKFILE"
+
+flock -n "$LOCKFILE" -c '
+    while [ -s "$JOBSFILE" ]
+    do
+        truncate -s 0 "$JOBSFILE" || exit 1
+        /lib/kdump/load.sh
+    done'
--- a/70-kdump.rules.in
+++ b/70-kdump.rules.in
@@ -20,7 +20,7 @@ GOTO="kdump_end"
 
 # Reload only if panic kernel is already loaded
 LABEL="kdump_try_restart"
-PROGRAM="/bin/cat /sys/kernel/kexec_crash_loaded", RESULT!="0", RUN+="/lib/kdump/load.sh"
+PROGRAM="/bin/cat /sys/kernel/kexec_crash_loaded", RESULT!="0", RUN+="/lib/kdump/load-once.sh"
 
 LABEL="kdump_end"
 @endif