diff options
| -rw-r--r-- | include/sys/zfs_ioctl.h | 9 | ||||
| -rw-r--r-- | module/zfs/zfs_ioctl.c | 61 |
2 files changed, 52 insertions, 18 deletions
diff --git a/include/sys/zfs_ioctl.h b/include/sys/zfs_ioctl.h index 0ab095c1a..c7bd789e8 100644 --- a/include/sys/zfs_ioctl.h +++ b/include/sys/zfs_ioctl.h @@ -371,8 +371,15 @@ enum zfsdev_state_type { ZST_ALL, }; +/* + * The zfsdev_state_t structure is managed as a singly-linked list + * from which items are never deleted. This allows for lock-free + * reading of the list so long as assignments to the zs_next and + * reads from zs_minor are performed atomically. Empty items are + * indicated by storing -1 into zs_minor. + */ typedef struct zfsdev_state { - list_node_t zs_next; /* next zfsdev_state_t link */ + struct zfsdev_state *zs_next; /* next zfsdev_state_t link */ struct file *zs_file; /* associated file struct */ minor_t zs_minor; /* made up minor number */ void *zs_onexit; /* onexit data */ diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c index 5f97ea454..db7683ad9 100644 --- a/module/zfs/zfs_ioctl.c +++ b/module/zfs/zfs_ioctl.c @@ -191,7 +191,7 @@ #include "zfs_comutil.h" kmutex_t zfsdev_state_lock; -list_t zfsdev_state_list; +zfsdev_state_t *zfsdev_state_list; extern void zfs_init(void); extern void zfs_fini(void); @@ -5447,11 +5447,9 @@ zfsdev_get_state_impl(minor_t minor, enum zfsdev_state_type which) { zfsdev_state_t *zs; - ASSERT(MUTEX_HELD(&zfsdev_state_lock)); - - for (zs = list_head(&zfsdev_state_list); zs != NULL; - zs = list_next(&zfsdev_state_list, zs)) { + for (zs = zfsdev_state_list; zs != NULL; zs = zs->zs_next) { if (zs->zs_minor == minor) { + smp_rmb(); switch (which) { case ZST_ONEXIT: return (zs->zs_onexit); @@ -5471,9 +5469,7 @@ zfsdev_get_state(minor_t minor, enum zfsdev_state_type which) { void *ptr; - mutex_enter(&zfsdev_state_lock); ptr = zfsdev_get_state_impl(minor, which); - mutex_exit(&zfsdev_state_lock); return (ptr); } @@ -5514,8 +5510,9 @@ zfsdev_minor_alloc(void) static int zfsdev_state_init(struct file *filp) { - zfsdev_state_t *zs; + zfsdev_state_t *zs, *zsprev = NULL; minor_t minor; + boolean_t newzs = B_FALSE; ASSERT(MUTEX_HELD(&zfsdev_state_lock)); @@ -5523,16 +5520,40 @@ zfsdev_state_init(struct file *filp) if (minor == 0) return (SET_ERROR(ENXIO)); - zs = kmem_zalloc(sizeof (zfsdev_state_t), KM_SLEEP); + for (zs = zfsdev_state_list; zs != NULL; zs = zs->zs_next) { + if (zs->zs_minor == -1) + break; + zsprev = zs; + } + + if (!zs) { + zs = kmem_zalloc(sizeof (zfsdev_state_t), KM_SLEEP); + newzs = B_TRUE; + } zs->zs_file = filp; - zs->zs_minor = minor; filp->private_data = zs; zfs_onexit_init((zfs_onexit_t **)&zs->zs_onexit); zfs_zevent_init((zfs_zevent_t **)&zs->zs_zevent); - list_insert_tail(&zfsdev_state_list, zs); + + /* + * In order to provide for lock-free concurrent read access + * to the minor list in zfsdev_get_state_impl(), new entries + * must be completely written before linking them into the + * list whereas existing entries are already linked; the last + * operation must be updating zs_minor (from -1 to the new + * value). + */ + if (newzs) { + zs->zs_minor = minor; + smp_wmb(); + zsprev->zs_next = zs; + } else { + smp_wmb(); + zs->zs_minor = minor; + } return (0); } @@ -5546,12 +5567,10 @@ zfsdev_state_destroy(struct file *filp) ASSERT(filp->private_data != NULL); zs = filp->private_data; + zs->zs_minor = -1; zfs_onexit_destroy(zs->zs_onexit); zfs_zevent_destroy(zs->zs_zevent); - list_remove(&zfsdev_state_list, zs); - kmem_free(zs, sizeof (zfsdev_state_t)); - return (0); } @@ -5762,8 +5781,8 @@ zfs_attach(void) int error; mutex_init(&zfsdev_state_lock, NULL, MUTEX_DEFAULT, NULL); - list_create(&zfsdev_state_list, sizeof (zfsdev_state_t), - offsetof(zfsdev_state_t, zs_next)); + zfsdev_state_list = kmem_zalloc(sizeof (zfsdev_state_t), KM_SLEEP); + zfsdev_state_list->zs_minor = -1; error = misc_register(&zfs_misc); if (error != 0) { @@ -5778,13 +5797,21 @@ static void zfs_detach(void) { int error; + zfsdev_state_t *zs, *zsprev = NULL; error = misc_deregister(&zfs_misc); if (error != 0) printk(KERN_INFO "ZFS: misc_deregister() failed %d\n", error); mutex_destroy(&zfsdev_state_lock); - list_destroy(&zfsdev_state_list); + + for (zs = zfsdev_state_list; zs != NULL; zs = zs->zs_next) { + if (zsprev) + kmem_free(zsprev, sizeof (zfsdev_state_t)); + zsprev = zs; + } + if (zsprev) + kmem_free(zsprev, sizeof (zfsdev_state_t)); } static void |