Illumos 3749 - zfs event processing should work on R/O root filesystems

3749 zfs event processing should work on R/O root filesystems
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Approved by: Christopher Siden <christopher.siden@delphix.com>

References:
  https://www.illumos.org/issues/3749
  https://github.com/illumos/illumos-gate/commit/3cb69f7

Porting notes:
- [include/sys/spa_impl.h]
  - ffe9d38 Add generic errata infrastructure
  - 1421c89 Add visibility in to arc_read
- [include/sys/fm/fs/zfs.h]
  - 2668527 Add linux events
  - 6283f55 Support custom build directories and move includes
- [module/zfs/spa_config.c]
  - Updated spa_config_sync() to match illumos with the exception
    of a Linux specific block.

Ported-by: kernelOfTruth kerneloftruth@gmail.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

include/sys/fm/fs/zfs.h

@@ -56,6 +56,7 @@ extern "C" {
 #define	FM_EREPORT_ZFS_IO_FAILURE		"io_failure"
 #define	FM_EREPORT_ZFS_PROBE_FAILURE		"probe_failure"
 #define	FM_EREPORT_ZFS_LOG_REPLAY		"log_replay"
+#define	FM_EREPORT_ZFS_CONFIG_CACHE_WRITE	"config_cache_write"
 #define	FM_EREPORT_ZFS_RESILVER_START		"resilver.start"
 #define	FM_EREPORT_ZFS_RESILVER_FINISH		"resilver.finish"
 #define	FM_EREPORT_ZFS_SCRUB_START		"scrub.start"

include/sys/spa_impl.h

@@ -252,6 +252,7 @@ struct spa {
 	uint64_t	spa_deadman_synctime;	/* deadman expiration timer */
 	uint64_t	spa_errata;		/* errata issues detected */
 	spa_stats_t	spa_stats;		/* assorted spa statistics */
+	hrtime_t	spa_ccw_fail_time;	/* Conf cache write fail time */
 
 	/*
 	 * spa_refcount & spa_config_lock must be the last elements

module/zfs/spa.c

@@ -82,6 +82,12 @@
 #include "zfs_prop.h"
 #include "zfs_comutil.h"
 
+/*
+ * The interval, in seconds, at which failed configuration cache file writes
+ * should be retried.
+ */
+static int zfs_ccw_retry_interval = 300;
+
 typedef enum zti_modes {
 	ZTI_MODE_FIXED,			/* value is # of threads (min 1) */
 	ZTI_MODE_BATCH,			/* cpu-intensive; value is ignored */
@@ -5912,13 +5918,34 @@ spa_async_resume(spa_t *spa)
 	mutex_exit(&spa->spa_async_lock);
 }
 
+static boolean_t
+spa_async_tasks_pending(spa_t *spa)
+{
+	uint_t non_config_tasks;
+	uint_t config_task;
+	boolean_t config_task_suspended;
+
+	non_config_tasks = spa->spa_async_tasks & ~SPA_ASYNC_CONFIG_UPDATE;
+	config_task = spa->spa_async_tasks & SPA_ASYNC_CONFIG_UPDATE;
+	if (spa->spa_ccw_fail_time == 0) {
+		config_task_suspended = B_FALSE;
+	} else {
+		config_task_suspended =
+		    (gethrtime() - spa->spa_ccw_fail_time) <
+		    (zfs_ccw_retry_interval * NANOSEC);
+	}
+
+	return (non_config_tasks || (config_task && !config_task_suspended));
+}
+
 static void
 spa_async_dispatch(spa_t *spa)
 {
 	mutex_enter(&spa->spa_async_lock);
-	if (spa->spa_async_tasks && !spa->spa_async_suspended &&
+	if (spa_async_tasks_pending(spa) &&
+	    !spa->spa_async_suspended &&
 	    spa->spa_async_thread == NULL &&
-	    rootdir != NULL && !vn_is_readonly(rootdir))
+	    rootdir != NULL)
 		spa->spa_async_thread = thread_create(NULL, 0,
 		    spa_async_thread, spa, 0, &p0, TS_RUN, maxclsyspri);
 	mutex_exit(&spa->spa_async_lock);

module/zfs/spa_config.c

@@ -26,6 +26,7 @@
  */
 
 #include <sys/spa.h>
+#include <sys/fm/fs/zfs.h>
 #include <sys/spa_impl.h>
 #include <sys/nvpair.h>
 #include <sys/uio.h>
@@ -145,22 +146,22 @@ out:
 	kobj_close_file(file);
 }
 
-static void
+static int
 spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 {
 	size_t buflen;
 	char *buf;
 	vnode_t *vp;
 	int oflags = FWRITE | FTRUNC | FCREAT | FOFFMAX;
-	int error;
 	char *temp;
+	int err;
 
 	/*
 	 * If the nvlist is empty (NULL), then remove the old cachefile.
 	 */
 	if (nvl == NULL) {
-		(void) vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
+		err = vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
-		return;
+		return (err);
 	}
 
 	/*
@@ -181,16 +182,16 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 	 * and overwritten in place.  In the event of an error the file is
 	 * unlinked to make sure we always have a consistent view of the data.
 	 */
-	error = vn_open(dp->scd_path, UIO_SYSSPACE, oflags, 0644, &vp, 0, 0);
+	err = vn_open(dp->scd_path, UIO_SYSSPACE, oflags, 0644, &vp, 0, 0);
-	if (error == 0) {
+	if (err == 0) {
-		error = vn_rdwr(UIO_WRITE, vp, buf, buflen, 0,
+		err = vn_rdwr(UIO_WRITE, vp, buf, buflen, 0,
 		    UIO_SYSSPACE, 0, RLIM64_INFINITY, kcred, NULL);
-		if (error == 0)
+		if (err == 0)
-			error = VOP_FSYNC(vp, FSYNC, kcred, NULL);
+			err = VOP_FSYNC(vp, FSYNC, kcred, NULL);
 
 		(void) VOP_CLOSE(vp, oflags, 1, 0, kcred, NULL);
 
-		if (error)
+		if (err)
 			(void) vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
 	}
 #else
@@ -201,13 +202,14 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 	 */
 	(void) snprintf(temp, MAXPATHLEN, "%s.tmp", dp->scd_path);
 
-	error = vn_open(temp, UIO_SYSSPACE, oflags, 0644, &vp, CRCREAT, 0);
+	err = vn_open(temp, UIO_SYSSPACE, oflags, 0644, &vp, CRCREAT, 0);
-	if (error == 0) {
+	if (err == 0) {
-		if (vn_rdwr(UIO_WRITE, vp, buf, buflen, 0, UIO_SYSSPACE,
+		err = vn_rdwr(UIO_WRITE, vp, buf, buflen, 0, UIO_SYSSPACE,
-		    0, RLIM64_INFINITY, kcred, NULL) == 0 &&
+		    0, RLIM64_INFINITY, kcred, NULL);
-		    VOP_FSYNC(vp, FSYNC, kcred, NULL) == 0) {
+		if (err == 0)
-			(void) vn_rename(temp, dp->scd_path, UIO_SYSSPACE);
+			err = VOP_FSYNC(vp, FSYNC, kcred, NULL);
-		}
+		if (err == 0)
+			err = vn_rename(temp, dp->scd_path, UIO_SYSSPACE);
 		(void) VOP_CLOSE(vp, oflags, 1, 0, kcred, NULL);
 	}
 
@@ -216,6 +218,7 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 
 	vmem_free(buf, buflen);
 	kmem_free(temp, MAXPATHLEN);
+	return (err);
 }
 
 /*
@@ -233,6 +236,8 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 	spa_config_dirent_t *dp, *tdp;
 	nvlist_t *nvl;
 	char *pool_name;
+	boolean_t ccw_failure;
+	int error = 0;
 
 	ASSERT(MUTEX_HELD(&spa_namespace_lock));
 
@@ -244,6 +249,7 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 	 * cachefile is changed, the new one is pushed onto this list, allowing
 	 * us to update previous cachefiles that no longer contain this pool.
 	 */
+	ccw_failure = B_FALSE;
 	for (dp = list_head(&target->spa_config_list); dp != NULL;
 	    dp = list_next(&target->spa_config_list, dp)) {
 		spa_t *spa = NULL;
@@ -290,10 +296,32 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 			mutex_exit(&spa->spa_props_lock);
 		}
 
-		spa_config_write(dp, nvl);
+		error = spa_config_write(dp, nvl);
+		if (error != 0)
+			ccw_failure = B_TRUE;
 		nvlist_free(nvl);
 	}
 
+	if (ccw_failure) {
+		/*
+		 * Keep trying so that configuration data is
+		 * written if/when any temporary filesystem
+		 * resource issues are resolved.
+		 */
+		if (target->spa_ccw_fail_time == 0) {
+			zfs_ereport_post(FM_EREPORT_ZFS_CONFIG_CACHE_WRITE,
+			    target, NULL, NULL, 0, 0);
+		}
+		target->spa_ccw_fail_time = gethrtime();
+		spa_async_request(target, SPA_ASYNC_CONFIG_UPDATE);
+	} else {
+		/*
+		 * Do not rate limit future attempts to update
+		 * the config cache.
+		 */
+		target->spa_ccw_fail_time = 0;
+	}
+
 	/*
 	 * Remove any config entries older than the current one.
 	 */