openzfs · tonyhutter · Feb 20, 2025 · Mar 26, 2025
diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c
@@ -7723,7 +7723,8 @@ import_checkpointed_state(char *target, nvlist_t *cfg, char **new_path)
 
 	if (cfg == NULL) {
 		zdb_set_skip_mmp(poolname);
-		error = spa_get_stats(poolname, &cfg, NULL, 0);
+		error = spa_get_stats(poolname, &cfg, NULL, 0,
+		    ZPOOL_LOCK_BEHAVIOR_DEFAULT);
 		if (error != 0) {
 			fatal("Tried to read config of pool \"%s\" but "
 			    "spa_get_stats() failed with error %d\n",

diff --git a/cmd/zpool/zpool_iter.c b/cmd/zpool/zpool_iter.c
@@ -118,6 +118,7 @@ pool_list_get(int argc, char **argv, zprop_list_t **proplist, zfs_type_t type,
     boolean_t literal, int *err)
 {
 	zpool_list_t *zlp;
+	int rc;
 
 	zlp = safe_malloc(sizeof (zpool_list_t));
 
@@ -137,7 +138,11 @@ pool_list_get(int argc, char **argv, zprop_list_t **proplist, zfs_type_t type,
 	zlp->zl_literal = literal;
 
 	if (argc == 0) {
-		(void) zpool_iter(g_zfs, add_pool, zlp);
+		rc = zpool_iter(g_zfs, add_pool, zlp);
+		if (rc != 0) {
+			free(zlp);
+			return (NULL);
+		}
 		zlp->zl_findall = B_TRUE;
 	} else {
 		int i;

diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
@@ -10979,6 +10979,32 @@ status_callback(zpool_handle_t *zhp, void *data)
 	return (0);
 }
 
+/*
+ * Set the zpool status lock behavior based off of the ZPOOL_LOCK_BEHAVIOR
+ * envvar.  If the var is not set, or an unknown value, then set the lock
+ * behavior to ZPOOL_LOCK_BEHAVIOR_DEFAULT.
+ */
+static void
+zpool_set_lock_behavior(void)
+{
+	char *str;
+	zpool_lock_behavior_t zpool_lock_behavior;
+
+	str = getenv("ZPOOL_LOCK_BEHAVIOR");
+	if (str == NULL)
+		zpool_lock_behavior = ZPOOL_LOCK_BEHAVIOR_DEFAULT;
+	else if (strcmp(str, "wait") == 0)
+		zpool_lock_behavior = ZPOOL_LOCK_BEHAVIOR_WAIT;
+	else if (strcmp(str, "trylock") == 0)
+		zpool_lock_behavior = ZPOOL_LOCK_BEHAVIOR_TRYLOCK;
+	else if (strcmp(str, "lockless") == 0)
+		zpool_lock_behavior = ZPOOL_LOCK_BEHAVIOR_LOCKLESS;
+	else
+		zpool_lock_behavior = ZPOOL_LOCK_BEHAVIOR_DEFAULT;
+
+	libzfs_set_lock_behavior(g_zfs, zpool_lock_behavior);
+}
+
 /*
  * zpool status [-c [script1,script2,...]] [-dDegiLpPstvx] [--power] ...
  *              [-T d|u] [pool] [interval [count]]
@@ -11152,6 +11178,8 @@ zpool_do_status(int argc, char **argv)
 		usage(B_FALSE);
 	}
 
+	zpool_set_lock_behavior();
+
 	for (;;) {
 		if (cb.cb_json) {
 			cb.cb_jsobj = zpool_json_schema(0, 1);

diff --git a/include/libzfs.h b/include/libzfs.h
@@ -264,6 +264,8 @@ _LIBZFS_H int zpool_create(libzfs_handle_t *, const char *, nvlist_t *,
     nvlist_t *, nvlist_t *);
 _LIBZFS_H int zpool_destroy(zpool_handle_t *, const char *);
 _LIBZFS_H int zpool_add(zpool_handle_t *, nvlist_t *, boolean_t check_ashift);
+_LIBZFS_H void libzfs_set_lock_behavior(libzfs_handle_t *,
+    zpool_lock_behavior_t);
 
 typedef struct splitflags {
 	/* do not split, but return the config that would be split off */

diff --git a/include/os/freebsd/spl/sys/mutex.h b/include/os/freebsd/spl/sys/mutex.h
@@ -72,4 +72,19 @@ typedef enum {
 #define	mutex_owned(lock)	sx_xlocked(lock)
 #define	mutex_owner(lock)	sx_xholder(lock)
 
+/*
+ * Poor-man's version of Linux kernel's down_timeout(). Try to acquire a mutex
+ * for 'ns' number of nanoseconds.  Returns 0 if mutex was acquired or ETIME
+ * if timeout occurred.
+ */
+static inline int mutex_enter_timeout(kmutex_t *mutex, uint64_t ns)
+{
+	hrtime_t end = gethrtime() + ns;
+	while (gethrtime() < end) {
+		if (mutex_tryenter(mutex))
+			return (0);	/* success */
+	}
+	return (ETIME);
+}
+
 #endif	/* _OPENSOLARIS_SYS_MUTEX_H_ */
diff --git a/include/os/linux/spl/sys/mutex.h b/include/os/linux/spl/sys/mutex.h
@@ -26,6 +26,7 @@
 #define	_SPL_MUTEX_H
 
 #include <sys/types.h>
+#include <sys/time.h>
 #include <linux/sched.h>
 #include <linux/mutex.h>
 #include <linux/lockdep.h>
@@ -187,4 +188,19 @@ spl_mutex_lockdep_on_maybe(kmutex_t *mp)			\
 	/* NOTE: do not dereference mp after this point */	\
 }
 
+/*
+ * Poor-man's version of Linux kernel's down_timeout(). Try to acquire a mutex
+ * for 'ns' number of nanoseconds.  Returns 0 if mutex was acquired or ETIME
+ * if timeout occurred.
+ */
+static inline int mutex_enter_timeout(kmutex_t *mutex, uint64_t ns)
+{
+	hrtime_t end = gethrtime() + ns;
+	while (gethrtime() < end) {
+		if (mutex_tryenter(mutex))
+			return (0);	/* success */
+	}
+	return (ETIME);
+}
+
 #endif /* _SPL_MUTEX_H */
diff --git a/include/sys/fs/zfs.h b/include/sys/fs/zfs.h
@@ -872,6 +872,9 @@ typedef struct zpool_load_policy {
 #define	ZPOOL_CONFIG_REBUILD_STATS	"org.openzfs:rebuild_stats"
 #define	ZPOOL_CONFIG_COMPATIBILITY	"compatibility"
 
+/* ZFS_IOC_POOL_STATS argument to for spa_namespace locking behavior */
+#define	ZPOOL_CONFIG_LOCK_BEHAVIOR	"lock_behavior"	/* not stored on disk */
+
 /*
  * The persistent vdev state is stored as separate values rather than a single
  * 'vdev_state' entry.  This is because a device can be in multiple states, such
@@ -1984,6 +1987,30 @@ enum zio_encrypt {
 	    ZFS_XA_NS_PREFIX_MATCH(LINUX_TRUSTED, name) || \
 	    ZFS_XA_NS_PREFIX_MATCH(LINUX_USER, name))
 
+/*
+ * Set locking behavior for zpool commands.
+ */
+typedef enum {
+	/* Wait to acquire the lock on the zpool config */
+	ZPOOL_LOCK_BEHAVIOR_WAIT = 0,
+	ZPOOL_LOCK_BEHAVIOR_DEFAULT = ZPOOL_LOCK_BEHAVIOR_WAIT,
+	/*
+	 * Return an error if it's taking an unnecessarily long time to
+	 * acquire the lock on the pool config (default 100ms)
+	 */
+	ZPOOL_LOCK_BEHAVIOR_TRYLOCK = 1,
+
+	/*
+	 * DANGER: THIS CAN CRASH YOUR SYSTEM
+	 *
+	 * If you can't acquire the pool config lock after 100ms then do a
+	 * a lockless lookup.  This should only be done in emergencies, as it
+	 * can crash the kernel module!
+	 */
+	ZPOOL_LOCK_BEHAVIOR_LOCKLESS = 2,
+	ZPOOL_LOCK_BEHAVIOR_END = 3	/* last entry marker */
+} zpool_lock_behavior_t;
+
 #ifdef	__cplusplus
 }
 #endif

diff --git a/include/sys/spa.h b/include/sys/spa.h
@@ -742,10 +742,13 @@ typedef enum trim_type {
 
 /* state manipulation functions */
 extern int spa_open(const char *pool, spa_t **, const void *tag);
+extern int spa_open_common_lock_behavior(const char *pool, spa_t **spapp,
+    const void *tag, nvlist_t *nvpolicy, nvlist_t **config,
+    zpool_lock_behavior_t zpool_lock_behavior);
 extern int spa_open_rewind(const char *pool, spa_t **, const void *tag,
     nvlist_t *policy, nvlist_t **config);
 extern int spa_get_stats(const char *pool, nvlist_t **config, char *altroot,
-    size_t buflen);
+    size_t buflen, zpool_lock_behavior_t zpool_lock_behavior);
 extern int spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
     nvlist_t *zplprops, struct dsl_crypto_params *dcp);
 extern int spa_import(char *pool, nvlist_t *config, nvlist_t *props,
@@ -851,10 +854,13 @@ extern kcondvar_t spa_namespace_cv;
 
 extern void spa_write_cachefile(spa_t *, boolean_t, boolean_t, boolean_t);
 extern void spa_config_load(void);
-extern int spa_all_configs(uint64_t *generation, nvlist_t **pools);
+extern int spa_all_configs(uint64_t *generation, nvlist_t **pools,
+    zpool_lock_behavior_t zpool_lock_behavior);
 extern void spa_config_set(spa_t *spa, nvlist_t *config);
 extern nvlist_t *spa_config_generate(spa_t *spa, vdev_t *vd, uint64_t txg,
     int getstats);
+extern nvlist_t *spa_config_generate_lock_behavior(spa_t *spa, vdev_t *vd,
+    uint64_t txg, int getstats, zpool_lock_behavior_t zpool_lock_behavior);
 extern void spa_config_update(spa_t *spa, int what);
 extern int spa_config_parse(spa_t *spa, vdev_t **vdp, nvlist_t *nv,
     vdev_t *parent, uint_t id, int atype);
@@ -866,9 +872,11 @@ extern int spa_config_parse(spa_t *spa, vdev_t **vdp, nvlist_t *nv,
 
 /* Namespace manipulation */
 extern spa_t *spa_lookup(const char *name);
+extern spa_t *spa_lookup_lockless(const char *name);
 extern spa_t *spa_add(const char *name, nvlist_t *config, const char *altroot);
 extern void spa_remove(spa_t *spa);
 extern spa_t *spa_next(spa_t *prev);
+extern spa_t *spa_next_lockless(spa_t *prev);
 
 /* Refcount functions */
 extern void spa_open_ref(spa_t *spa, const void *tag);

diff --git a/include/sys/spa_impl.h b/include/sys/spa_impl.h
@@ -491,6 +491,7 @@ extern void spa_set_deadman_synctime(hrtime_t ns);
 extern void spa_set_deadman_ziotime(hrtime_t ns);
 extern const char *spa_history_zone(void);
 extern const char *zfs_active_allocator;
+extern unsigned int spa_namespace_trylock_ms;
 extern int param_set_active_allocator_common(const char *val);
 
 #ifdef	__cplusplus

diff --git a/include/sys/zfs_context.h b/include/sys/zfs_context.h
@@ -277,6 +277,7 @@ extern void mutex_enter(kmutex_t *mp);
 extern int mutex_enter_check_return(kmutex_t *mp);
 extern void mutex_exit(kmutex_t *mp);
 extern int mutex_tryenter(kmutex_t *mp);
+extern int mutex_enter_timeout(kmutex_t *mp, uint64_t ns);
 
 #define	NESTED_SINGLE 1
 #define	mutex_enter_nested(mp, class) mutex_enter(mp)

diff --git a/lib/libzfs/libzfs.abi b/lib/libzfs/libzfs.abi
@@ -218,6 +218,7 @@
     <elf-symbol name='libzfs_run_process' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='libzfs_run_process_get_stdout' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='libzfs_run_process_get_stdout_nopath' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='libzfs_set_lock_behavior' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='list_create' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='list_destroy' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='list_head' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
@@ -2073,6 +2074,15 @@
       <enumerator name='ZPROP_SRC_RECEIVED' value='32'/>
     </enum-decl>
     <typedef-decl name='zprop_source_t' type-id='5903f80e' id='a2256d42'/>
+    <enum-decl name='zpool_lock_behavior_t' naming-typedef-id='8b691302' id='cdf5aa2e'>
+      <underlying-type type-id='9cac1fee'/>
+      <enumerator name='ZPOOL_LOCK_BEHAVIOR_WAIT' value='0'/>
+      <enumerator name='ZPOOL_LOCK_BEHAVIOR_DEFAULT' value='0'/>
+      <enumerator name='ZPOOL_LOCK_BEHAVIOR_TRYLOCK' value='1'/>
+      <enumerator name='ZPOOL_LOCK_BEHAVIOR_LOCKLESS' value='2'/>
+      <enumerator name='ZPOOL_LOCK_BEHAVIOR_END' value='3'/>
+    </enum-decl>
+    <typedef-decl name='zpool_lock_behavior_t' type-id='cdf5aa2e' id='8b691302'/>
     <class-decl name='nvlist' size-in-bits='192' is-struct='yes' visibility='default' id='ac266fd9'>
       <data-member access='public' layout-offset-in-bits='0'>
         <var-decl name='nvl_version' type-id='3ff5601b' visibility='default'/>
@@ -2212,7 +2222,7 @@
     <typedef-decl name='__uint32_t' type-id='f0981eeb' id='62f1140c'/>
     <typedef-decl name='__uint64_t' type-id='7359adad' id='8910171f'/>
     <typedef-decl name='size_t' type-id='7359adad' id='b59d7dce'/>
-    <class-decl name='libzfs_handle' size-in-bits='18240' is-struct='yes' visibility='default' id='c8a9d9d8'>
+    <class-decl name='libzfs_handle' size-in-bits='18304' is-struct='yes' visibility='default' id='c8a9d9d8'>
       <data-member access='public' layout-offset-in-bits='0'>
         <var-decl name='libzfs_error' type-id='95e97e5e' visibility='default'/>
       </data-member>
@@ -2270,6 +2280,9 @@
       <data-member access='public' layout-offset-in-bits='18176'>
         <var-decl name='libfetch_load_error' type-id='26a90f95' visibility='default'/>
       </data-member>
+      <data-member access='public' layout-offset-in-bits='18240'>
+        <var-decl name='zpool_lock_behavior' type-id='8b691302' visibility='default'/>
+      </data-member>
     </class-decl>
     <class-decl name='zfs_handle' size-in-bits='4928' is-struct='yes' visibility='default' id='f6ee4445'>
       <data-member access='public' layout-offset-in-bits='0'>
@@ -2949,6 +2962,12 @@
       <parameter type-id='b65f7fd1'/>
       <return type-id='95e97e5e'/>
     </function-decl>
+    <function-decl name='nvlist_alloc' visibility='default' binding='global' size-in-bits='64'>
+      <parameter type-id='857bb57e'/>
+      <parameter type-id='3502e3ff'/>
+      <parameter type-id='95e97e5e'/>
+      <return type-id='95e97e5e'/>
+    </function-decl>
     <function-decl name='nvlist_free' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='5ce45b60'/>
       <return type-id='48b5725f'/>
@@ -2959,6 +2978,12 @@
       <parameter type-id='95e97e5e'/>
       <return type-id='95e97e5e'/>
     </function-decl>
+    <function-decl name='nvlist_add_uint64' visibility='default' binding='global' size-in-bits='64'>
+      <parameter type-id='5ce45b60'/>
+      <parameter type-id='80f4b756'/>
+      <parameter type-id='9c313c2d'/>
+      <return type-id='95e97e5e'/>
+    </function-decl>
     <function-decl name='nvlist_lookup_nvlist' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='5ce45b60'/>
       <parameter type-id='80f4b756'/>
@@ -3054,6 +3079,12 @@
       <parameter type-id='b59d7dce'/>
       <return type-id='48b5725f'/>
     </function-decl>
+    <function-decl name='zcmd_write_src_nvlist' visibility='default' binding='global' size-in-bits='64'>
+      <parameter type-id='b0382bb3'/>
+      <parameter type-id='e4ec4540'/>
+      <parameter type-id='5ce45b60'/>
+      <return type-id='48b5725f'/>
+    </function-decl>
     <function-decl name='zcmd_expand_dst_nvlist' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='b0382bb3'/>
       <parameter type-id='e4ec4540'/>
@@ -3563,12 +3594,6 @@
       <parameter type-id='80f4b756'/>
       <return type-id='58603c44'/>
     </function-decl>
-    <function-decl name='nvlist_add_uint64' visibility='default' binding='global' size-in-bits='64'>
-      <parameter type-id='5ce45b60'/>
-      <parameter type-id='80f4b756'/>
-      <parameter type-id='9c313c2d'/>
-      <return type-id='95e97e5e'/>
-    </function-decl>
     <function-decl name='nvlist_add_string' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='5ce45b60'/>
       <parameter type-id='80f4b756'/>
@@ -4324,12 +4349,6 @@
       <parameter type-id='c19b74c3'/>
       <return type-id='c19b74c3'/>
     </function-decl>
-    <function-decl name='nvlist_alloc' visibility='default' binding='global' size-in-bits='64'>
-      <parameter type-id='857bb57e'/>
-      <parameter type-id='3502e3ff'/>
-      <parameter type-id='95e97e5e'/>
-      <return type-id='95e97e5e'/>
-    </function-decl>
     <function-decl name='nvlist_size' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='5ce45b60'/>
       <parameter type-id='78c01427'/>
@@ -4948,12 +4967,6 @@
       <parameter type-id='2e45de5d'/>
       <return type-id='95e97e5e'/>
     </function-decl>
-    <function-decl name='zcmd_write_src_nvlist' visibility='default' binding='global' size-in-bits='64'>
-      <parameter type-id='b0382bb3'/>
-      <parameter type-id='e4ec4540'/>
-      <parameter type-id='5ce45b60'/>
-      <return type-id='48b5725f'/>
-    </function-decl>
     <function-decl name='changelist_prefix' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='0d41d328'/>
       <return type-id='95e97e5e'/>
@@ -8550,6 +8563,11 @@
       <parameter type-id='7292109c' name='lines_cnt'/>
       <return type-id='95e97e5e'/>
     </function-decl>
+    <function-decl name='libzfs_set_lock_behavior' mangled-name='libzfs_set_lock_behavior' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='libzfs_set_lock_behavior'>
+      <parameter type-id='b0382bb3' name='hdl'/>
+      <parameter type-id='8b691302' name='zpool_lock_behavior'/>
+      <return type-id='48b5725f'/>
+    </function-decl>
   </abi-instr>
   <abi-instr address-size='64' path='lib/libzfs/os/linux/libzfs_mount_os.c' language='LANG_C99'>
     <pointer-type-def type-id='7359adad' size-in-bits='64' id='1d2c2b85'/>