From 474c6adf8f4972990de661f1c57e3d3f187a4a3a Mon Sep 17 00:00:00 2001
From: Matthew Rosato <mjrosato@linux.ibm.com>
Date: Thu, 11 Apr 2024 14:36:34 -0400
Subject: [PATCH] libap: use custom wait time for file locks

If many invocations of mdevctl occur simultaneously (as can happen with
libvirt) then waiting for 5-60 seconds per lock retry is simply too long.
Anticipating this possibility, retry more frequently but also attempt
significantly more retries than before.

Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Reviewed-by: Marc Hartmayer <marc@linux.ibm.com>
Tested-by: Marc Hartmayer <marc@linux.ibm.com>
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
---
 include/lib/ap.h |  4 +++-
 libap/ap.c       | 26 ++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/include/lib/ap.h b/include/lib/ap.h
index 58baeeb5..057a78e4 100644
--- a/include/lib/ap.h
+++ b/include/lib/ap.h
@@ -21,7 +21,9 @@
 #define AP_UDEV_FILE "/etc/udev/rules.d/41-ap.rules"
 #define AP_LOCKFILE "/run/lock/s390apconfig.lock"
 
-#define AP_LOCK_RETRIES 15
+#define AP_LOCK_RETRIES 3000
+#define AP_LOCK_DELAY_US 30000 /* wait at least 30ms between lock retries */
+#define AP_LOCK_VARIANCE_US 3000  /* or as much as 33ms */
 
 /* apmask and aqmask are each represented as 67 character strings with:
  *  '0x' leading characters
diff --git a/libap/ap.c b/libap/ap.c
index e683b291..5c2f406d 100644
--- a/libap/ap.c
+++ b/libap/ap.c
@@ -11,12 +11,15 @@
 #include <dirent.h>
 #include <err.h>
 #include <errno.h>
+#include <limits.h>
 #include <stdarg.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <sys/time.h>
 
 #ifdef HAVE_JSONC
 #include <json-c/json.h>
@@ -698,6 +701,20 @@ void ap_list_remove_all(struct util_list *list)
 	}
 }
 
+static unsigned int random_delay(void)
+{
+	static bool libap_seed = true;
+	struct timeval t;
+
+	if (libap_seed) {
+		gettimeofday(&t, NULL);
+		srand((unsigned int)((t.tv_sec + t.tv_usec) % UINT_MAX));
+		libap_seed = false;
+	}
+
+	return AP_LOCK_DELAY_US + (rand() % AP_LOCK_VARIANCE_US);
+}
+
 /**
  * Acquire the ap config lock using this Process ID
  *
@@ -707,7 +724,9 @@ void ap_list_remove_all(struct util_list *list)
  */
 int ap_get_lock(void)
 {
-	return util_lockfile_lock(AP_LOCKFILE, AP_LOCK_RETRIES);
+	unsigned int delay = random_delay();
+
+	return util_lockfile_lock_cw(AP_LOCKFILE, AP_LOCK_RETRIES, delay, delay);
 }
 
 /**
@@ -719,7 +738,10 @@ int ap_get_lock(void)
  */
 int ap_get_lock_callout(void)
 {
-	return util_lockfile_parent_lock(AP_LOCKFILE, AP_LOCK_RETRIES);
+	unsigned int delay = random_delay();
+
+	return util_lockfile_parent_lock_cw(AP_LOCKFILE, AP_LOCK_RETRIES, delay,
+					    delay);
 }
 
 /**