File lvmetad_tokent_mismatch_retry.patch of Package lvm2.3693

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File lvmetad_tokent_mismatch_retry.patch of Package lvm2.3693

Index: LVM2.2.02.98/lib/cache/lvmetad.c
===================================================================
--- LVM2.2.02.98.orig/lib/cache/lvmetad.c
+++ LVM2.2.02.98/lib/cache/lvmetad.c
@@ -23,6 +23,9 @@
 #include "assert.h"
 #include "crc.h"
 
+#define SCAN_TIMEOUT_SECONDS    80
+#define MAX_RESCANS		10 /* Maximum number of times to scan all PVs and retry if the daemon returns a token mismatch error */
+
 static daemon_handle _lvmetad;
 static int _lvmetad_use = 0;
 static int _lvmetad_connected = 0;
@@ -128,7 +131,10 @@ static daemon_reply _lvmetad_send(const
 	va_list ap;
 	daemon_reply repl;
 	daemon_request req;
-	int try = 0;
+	unsigned num_rescans = 0;
+	unsigned total_usecs_waited = 0;
+	unsigned max_remaining_sleep_times = 1;
+	unsigned wait_usecs;
 
 retry:
 	req = daemon_request_make(id);
@@ -144,15 +150,35 @@ retry:
 
 	daemon_request_destroy(req);
 
+	/** If another process is trying to scan, it might have the
+	 * same future token id and it's better to wait and avoid doing
+	 * the work multiple times. For the case where the future token is
+	 * different, the wait is randomized so that multiple waiting
+	 * processes do not start scanning all at once.
+	 *
+	 * If the token is mismatched because of global_filter changes,
+	 * we re-scan immediately, but if we lose the potential race for
+	 * the update, we back off for a short while (0.05-0.5 seconds) and
+	 * try again.
+	 */
 	if (!repl.error && !strcmp(daemon_reply_str(repl, "response", ""), "token_mismatch") &&
-	    try < 2 && !test_mode()) {
-		if (lvmetad_pvscan_all_devs(_lvmetad_cmd, NULL)) {
-			++ try;
-			daemon_reply_destroy(repl);
-			goto retry;
+	    num_rescans < MAX_RESCANS && total_usecs_waited < (SCAN_TIMEOUT_SECONDS * 1000000) && !test_mode()) {
+		if (!strcmp(daemon_reply_str(repl, "expected", ""), "update in progress") ||
+		    max_remaining_sleep_times) {
+			wait_usecs = 50000 + lvm_even_rand(&_lvmetad_cmd->rand_seed, 450000); /* between 0.05s and 0.5s */
+			(void) usleep(wait_usecs);
+			total_usecs_waited += wait_usecs;
+			if (max_remaining_sleep_times)
+				max_remaining_sleep_times--;	/* Sleep once before rescanning the first time, then 5 times each time after that. */
+		} else {
+			/* If the re-scan fails here, we try again later. */
+			(void) lvmetad_pvscan_all_devs(_lvmetad_cmd, NULL);
+			num_rescans++;
+			max_remaining_sleep_times = 5;
 		}
+		daemon_reply_destroy(repl);
+		goto retry;
 	}
-
 	return repl;
 }
 
Index: LVM2.2.02.98/lib/misc/lvm-wrappers.c
===================================================================
--- LVM2.2.02.98.orig/lib/misc/lvm-wrappers.c
+++ LVM2.2.02.98/lib/misc/lvm-wrappers.c
@@ -117,3 +117,25 @@ int read_urandom(void *buf, size_t len)
 	return 1;
 }
 
+/*
+ * Return random integer in [0,max) interval
+ *
+ * The loop rejects numbers that come from an "incomplete" slice of the
+ * RAND_MAX space.  Considering the number space [0, RAND_MAX] is divided
+ * into some "max"-sized slices and at most a single smaller slice,
+ * between [n*max, RAND_MAX] for suitable n, numbers from this last slice
+ * are discarded because they could distort the distribution in favour of
+ * smaller numbers.
+ */
+unsigned lvm_even_rand(unsigned *seed, unsigned max)
+{
+        unsigned r, ret;
+
+        do {
+                r = (unsigned) rand_r(seed);
+                ret = r % max;
+        } while (r - ret > RAND_MAX - max);
+
+        return ret;
+}
+

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File lvmetad_tokent_mismatch_retry.patch of Package lvm2.3693

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