/* * CDDL HEADER START * * The contents of this file are subject to the terms of the * Common Development and Distribution License (the "License"). * You may not use this file except in compliance with the License. * * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE * or http://www.opensolaris.org/os/licensing. * See the License for the specific language governing permissions * and limitations under the License. * * When distributing Covered Code, include this CDDL HEADER in each * file and include the License file at usr/src/OPENSOLARIS.LICENSE. * If applicable, add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your own identifying * information: Portions Copyright [yyyy] [name of copyright owner] * * CDDL HEADER END */ /* * Copyright 2010 Sun Microsystems, Inc. All rights reserved. * Use is subject to license terms. */ /* * Copyright (c) 2012 by Delphix. All rights reserved. */ /* * This file contains the code to implement file range locking in * ZFS, although there isn't much specific to ZFS (all that comes to mind is * support for growing the blocksize). * * Interface * --------- * Defined in zfs_rlock.h but essentially: * rl = zfs_range_lock(zp, off, len, lock_type); * zfs_range_unlock(rl); * zfs_range_reduce(rl, off, len); * * AVL tree * -------- * An AVL tree is used to maintain the state of the existing ranges * that are locked for exclusive (writer) or shared (reader) use. * The starting range offset is used for searching and sorting the tree. * * Common case * ----------- * The (hopefully) usual case is of no overlaps or contention for * locks. On entry to zfs_lock_range() a rl_t is allocated; the tree * searched that finds no overlap, and *this* rl_t is placed in the tree. * * Overlaps/Reference counting/Proxy locks * --------------------------------------- * The avl code only allows one node at a particular offset. Also it's very * inefficient to search through all previous entries looking for overlaps * (because the very 1st in the ordered list might be at offset 0 but * cover the whole file). * So this implementation uses reference counts and proxy range locks. * Firstly, only reader locks use reference counts and proxy locks, * because writer locks are exclusive. * When a reader lock overlaps with another then a proxy lock is created * for that range and replaces the original lock. If the overlap * is exact then the reference count of the proxy is simply incremented. * Otherwise, the proxy lock is split into smaller lock ranges and * new proxy locks created for non overlapping ranges. * The reference counts are adjusted accordingly. * Meanwhile, the orginal lock is kept around (this is the callers handle) * and its offset and length are used when releasing the lock. * * Thread coordination * ------------------- * In order to make wakeups efficient and to ensure multiple continuous * readers on a range don't starve a writer for the same range lock, * two condition variables are allocated in each rl_t. * If a writer (or reader) can't get a range it initialises the writer * (or reader) cv; sets a flag saying there's a writer (or reader) waiting; * and waits on that cv. When a thread unlocks that range it wakes up all * writers then all readers before destroying the lock. * * Append mode writes * ------------------ * Append mode writes need to lock a range at the end of a file. * The offset of the end of the file is determined under the * range locking mutex, and the lock type converted from RL_APPEND to * RL_WRITER and the range locked. * * Grow block handling * ------------------- * ZFS supports multiple block sizes currently upto 128K. The smallest * block size is used for the file which is grown as needed. During this * growth all other writers and readers must be excluded. * So if the block size needs to be grown then the whole file is * exclusively locked, then later the caller will reduce the lock * range to just the range to be written using zfs_reduce_range. */ #include <sys/zfs_rlock.h> /* * Check if a write lock can be grabbed, or wait and recheck until available. */ static void zfs_range_lock_writer(znode_t *zp, rl_t *new) { avl_tree_t *tree = &zp->z_range_avl; rl_t *rl; avl_index_t where; uint64_t end_size; uint64_t off = new->r_off; uint64_t len = new->r_len; for (;;) { /* * Range locking is also used by zvol and uses a * dummied up znode. However, for zvol, we don't need to * append or grow blocksize, and besides we don't have * a "sa" data or zfs_sb_t - so skip that processing. * * Yes, this is ugly, and would be solved by not handling * grow or append in range lock code. If that was done then * we could make the range locking code generically available * to other non-zfs consumers. */ if (!zp->z_is_zvol) { /* caller is ZPL */ /* * If in append mode pick up the current end of file. * This is done under z_range_lock to avoid races. */ if (new->r_type == RL_APPEND) new->r_off = zp->z_size; /* * If we need to grow the block size then grab the whole * file range. This is also done under z_range_lock to * avoid races. */ end_size = MAX(zp->z_size, new->r_off + len); if (end_size > zp->z_blksz && (!ISP2(zp->z_blksz) || zp->z_blksz < ZTOZSB(zp)->z_max_blksz)) { new->r_off = 0; new->r_len = UINT64_MAX; } } /* * First check for the usual case of no locks */ if (avl_numnodes(tree) == 0) { new->r_type = RL_WRITER; /* convert to writer */ avl_add(tree, new); return; } /* * Look for any locks in the range. */ rl = avl_find(tree, new, &where); if (rl) goto wait; /* already locked at same offset */ rl = (rl_t *)avl_nearest(tree, where, AVL_AFTER); if (rl && (rl->r_off < new->r_off + new->r_len)) goto wait; rl = (rl_t *)avl_nearest(tree, where, AVL_BEFORE); if (rl && rl->r_off + rl->r_len > new->r_off) goto wait; new->r_type = RL_WRITER; /* convert possible RL_APPEND */ avl_insert(tree, new, where); return; wait: if (!rl->r_write_wanted) { cv_init(&rl->r_wr_cv, NULL, CV_DEFAULT, NULL); rl->r_write_wanted = B_TRUE; } cv_wait(&rl->r_wr_cv, &zp->z_range_lock); /* reset to original */ new->r_off = off; new->r_len = len; } } /* * If this is an original (non-proxy) lock then replace it by * a proxy and return the proxy. */ static rl_t * zfs_range_proxify(avl_tree_t *tree, rl_t *rl) { rl_t *proxy; if (rl->r_proxy) return (rl); /* already a proxy */ ASSERT3U(rl->r_cnt, ==, 1); ASSERT(rl->r_write_wanted == B_FALSE); ASSERT(rl->r_read_wanted == B_FALSE); avl_remove(tree, rl); rl->r_cnt = 0; /* create a proxy range lock */ proxy = kmem_alloc(sizeof (rl_t), KM_PUSHPAGE); proxy->r_off = rl->r_off; proxy->r_len = rl->r_len; proxy->r_cnt = 1; proxy->r_type = RL_READER; proxy->r_proxy = B_TRUE; proxy->r_write_wanted = B_FALSE; proxy->r_read_wanted = B_FALSE; avl_add(tree, proxy); return (proxy); } /* * Split the range lock at the supplied offset * returning the *front* proxy. */ static rl_t * zfs_range_split(avl_tree_t *tree, rl_t *rl, uint64_t off) { rl_t *front, *rear; ASSERT3U(rl->r_len, >, 1); ASSERT3U(off, >, rl->r_off); ASSERT3U(off, <, rl->r_off + rl->r_len); ASSERT(rl->r_write_wanted == B_FALSE); ASSERT(rl->r_read_wanted == B_FALSE); /* create the rear proxy range lock */ rear = kmem_alloc(sizeof (rl_t), KM_PUSHPAGE); rear->r_off = off; rear->r_len = rl->r_off + rl->r_len - off; rear->r_cnt = rl->r_cnt; rear->r_type = RL_READER; rear->r_proxy = B_TRUE; rear->r_write_wanted = B_FALSE; rear->r_read_wanted = B_FALSE; front = zfs_range_proxify(tree, rl); front->r_len = off - rl->r_off; avl_insert_here(tree, rear, front, AVL_AFTER); return (front); } /* * Create and add a new proxy range lock for the supplied range. */ static void zfs_range_new_proxy(avl_tree_t *tree, uint64_t off, uint64_t len) { rl_t *rl; ASSERT(len); rl = kmem_alloc(sizeof (rl_t), KM_PUSHPAGE); rl->r_off = off; rl->r_len = len; rl->r_cnt = 1; rl->r_type = RL_READER; rl->r_proxy = B_TRUE; rl->r_write_wanted = B_FALSE; rl->r_read_wanted = B_FALSE; avl_add(tree, rl); } static void zfs_range_add_reader(avl_tree_t *tree, rl_t *new, rl_t *prev, avl_index_t where) { rl_t *next; uint64_t off = new->r_off; uint64_t len = new->r_len; /* * prev arrives either: * - pointing to an entry at the same offset * - pointing to the entry with the closest previous offset whose * range may overlap with the new range * - null, if there were no ranges starting before the new one */ if (prev) { if (prev->r_off + prev->r_len <= off) { prev = NULL; } else if (prev->r_off != off) { /* * convert to proxy if needed then * split this entry and bump ref count */ prev = zfs_range_split(tree, prev, off); prev = AVL_NEXT(tree, prev); /* move to rear range */ } } ASSERT((prev == NULL) || (prev->r_off == off)); if (prev) next = prev; else next = (rl_t *)avl_nearest(tree, where, AVL_AFTER); if (next == NULL || off + len <= next->r_off) { /* no overlaps, use the original new rl_t in the tree */ avl_insert(tree, new, where); return; } if (off < next->r_off) { /* Add a proxy for initial range before the overlap */ zfs_range_new_proxy(tree, off, next->r_off - off); } new->r_cnt = 0; /* will use proxies in tree */ /* * We now search forward through the ranges, until we go past the end * of the new range. For each entry we make it a proxy if it * isn't already, then bump its reference count. If there's any * gaps between the ranges then we create a new proxy range. */ for (prev = NULL; next; prev = next, next = AVL_NEXT(tree, next)) { if (off + len <= next->r_off) break; if (prev && prev->r_off + prev->r_len < next->r_off) { /* there's a gap */ ASSERT3U(next->r_off, >, prev->r_off + prev->r_len); zfs_range_new_proxy(tree, prev->r_off + prev->r_len, next->r_off - (prev->r_off + prev->r_len)); } if (off + len == next->r_off + next->r_len) { /* exact overlap with end */ next = zfs_range_proxify(tree, next); next->r_cnt++; return; } if (off + len < next->r_off + next->r_len) { /* new range ends in the middle of this block */ next = zfs_range_split(tree, next, off + len); next->r_cnt++; return; } ASSERT3U(off + len, >, next->r_off + next->r_len); next = zfs_range_proxify(tree, next); next->r_cnt++; } /* Add the remaining end range. */ zfs_range_new_proxy(tree, prev->r_off + prev->r_len, (off + len) - (prev->r_off + prev->r_len)); } /* * Check if a reader lock can be grabbed, or wait and recheck until available. */ static void zfs_range_lock_reader(znode_t *zp, rl_t *new) { avl_tree_t *tree = &zp->z_range_avl; rl_t *prev, *next; avl_index_t where; uint64_t off = new->r_off; uint64_t len = new->r_len; /* * Look for any writer locks in the range. */ retry: prev = avl_find(tree, new, &where); if (prev == NULL) prev = (rl_t *)avl_nearest(tree, where, AVL_BEFORE); /* * Check the previous range for a writer lock overlap. */ if (prev && (off < prev->r_off + prev->r_len)) { if ((prev->r_type == RL_WRITER) || (prev->r_write_wanted)) { if (!prev->r_read_wanted) { cv_init(&prev->r_rd_cv, NULL, CV_DEFAULT, NULL); prev->r_read_wanted = B_TRUE; } cv_wait(&prev->r_rd_cv, &zp->z_range_lock); goto retry; } if (off + len < prev->r_off + prev->r_len) goto got_lock; } /* * Search through the following ranges to see if there's * write lock any overlap. */ if (prev) next = AVL_NEXT(tree, prev); else next = (rl_t *)avl_nearest(tree, where, AVL_AFTER); for (; next; next = AVL_NEXT(tree, next)) { if (off + len <= next->r_off) goto got_lock; if ((next->r_type == RL_WRITER) || (next->r_write_wanted)) { if (!next->r_read_wanted) { cv_init(&next->r_rd_cv, NULL, CV_DEFAULT, NULL); next->r_read_wanted = B_TRUE; } cv_wait(&next->r_rd_cv, &zp->z_range_lock); goto retry; } if (off + len <= next->r_off + next->r_len) goto got_lock; } got_lock: /* * Add the read lock, which may involve splitting existing * locks and bumping ref counts (r_cnt). */ zfs_range_add_reader(tree, new, prev, where); } /* * Lock a range (offset, length) as either shared (RL_READER) * or exclusive (RL_WRITER). Returns the range lock structure * for later unlocking or reduce range (if entire file * previously locked as RL_WRITER). */ rl_t * zfs_range_lock(znode_t *zp, uint64_t off, uint64_t len, rl_type_t type) { rl_t *new; ASSERT(type == RL_READER || type == RL_WRITER || type == RL_APPEND); new = kmem_alloc(sizeof (rl_t), KM_PUSHPAGE); new->r_zp = zp; new->r_off = off; if (len + off < off) /* overflow */ len = UINT64_MAX - off; new->r_len = len; new->r_cnt = 1; /* assume it's going to be in the tree */ new->r_type = type; new->r_proxy = B_FALSE; new->r_write_wanted = B_FALSE; new->r_read_wanted = B_FALSE; mutex_enter(&zp->z_range_lock); if (type == RL_READER) { /* * First check for the usual case of no locks */ if (avl_numnodes(&zp->z_range_avl) == 0) avl_add(&zp->z_range_avl, new); else zfs_range_lock_reader(zp, new); } else zfs_range_lock_writer(zp, new); /* RL_WRITER or RL_APPEND */ mutex_exit(&zp->z_range_lock); return (new); } static void zfs_range_free(void *arg) { rl_t *rl = arg; if (rl->r_write_wanted) cv_destroy(&rl->r_wr_cv); if (rl->r_read_wanted) cv_destroy(&rl->r_rd_cv); kmem_free(rl, sizeof (rl_t)); } /* * Unlock a reader lock */ static void zfs_range_unlock_reader(znode_t *zp, rl_t *remove, list_t *free_list) { avl_tree_t *tree = &zp->z_range_avl; rl_t *rl, *next = NULL; uint64_t len; /* * The common case is when the remove entry is in the tree * (cnt == 1) meaning there's been no other reader locks overlapping * with this one. Otherwise the remove entry will have been * removed from the tree and replaced by proxies (one or * more ranges mapping to the entire range). */ if (remove->r_cnt == 1) { avl_remove(tree, remove); if (remove->r_write_wanted) cv_broadcast(&remove->r_wr_cv); if (remove->r_read_wanted) cv_broadcast(&remove->r_rd_cv); list_insert_tail(free_list, remove); } else { ASSERT0(remove->r_cnt); ASSERT0(remove->r_write_wanted); ASSERT0(remove->r_read_wanted); /* * Find start proxy representing this reader lock, * then decrement ref count on all proxies * that make up this range, freeing them as needed. */ rl = avl_find(tree, remove, NULL); ASSERT(rl); ASSERT(rl->r_cnt); ASSERT(rl->r_type == RL_READER); for (len = remove->r_len; len != 0; rl = next) { len -= rl->r_len; if (len) { next = AVL_NEXT(tree, rl); ASSERT(next); ASSERT(rl->r_off + rl->r_len == next->r_off); ASSERT(next->r_cnt); ASSERT(next->r_type == RL_READER); } rl->r_cnt--; if (rl->r_cnt == 0) { avl_remove(tree, rl); if (rl->r_write_wanted) cv_broadcast(&rl->r_wr_cv); if (rl->r_read_wanted) cv_broadcast(&rl->r_rd_cv); list_insert_tail(free_list, rl); } } kmem_free(remove, sizeof (rl_t)); } } /* * Unlock range and destroy range lock structure. */ void zfs_range_unlock(rl_t *rl) { znode_t *zp = rl->r_zp; list_t free_list; rl_t *free_rl; ASSERT(rl->r_type == RL_WRITER || rl->r_type == RL_READER); ASSERT(rl->r_cnt == 1 || rl->r_cnt == 0); ASSERT(!rl->r_proxy); list_create(&free_list, sizeof (rl_t), offsetof(rl_t, rl_node)); mutex_enter(&zp->z_range_lock); if (rl->r_type == RL_WRITER) { /* writer locks can't be shared or split */ avl_remove(&zp->z_range_avl, rl); if (rl->r_write_wanted) cv_broadcast(&rl->r_wr_cv); if (rl->r_read_wanted) cv_broadcast(&rl->r_rd_cv); list_insert_tail(&free_list, rl); } else { /* * lock may be shared, let zfs_range_unlock_reader() * release the zp->z_range_lock lock and free the rl_t */ zfs_range_unlock_reader(zp, rl, &free_list); } mutex_exit(&zp->z_range_lock); while ((free_rl = list_head(&free_list)) != NULL) { list_remove(&free_list, free_rl); zfs_range_free(free_rl); } list_destroy(&free_list); } /* * Reduce range locked as RL_WRITER from whole file to specified range. * Asserts the whole file is exclusivly locked and so there's only one * entry in the tree. */ void zfs_range_reduce(rl_t *rl, uint64_t off, uint64_t len) { znode_t *zp = rl->r_zp; /* Ensure there are no other locks */ ASSERT(avl_numnodes(&zp->z_range_avl) == 1); ASSERT(rl->r_off == 0); ASSERT(rl->r_type == RL_WRITER); ASSERT(!rl->r_proxy); ASSERT3U(rl->r_len, ==, UINT64_MAX); ASSERT3U(rl->r_cnt, ==, 1); mutex_enter(&zp->z_range_lock); rl->r_off = off; rl->r_len = len; if (rl->r_write_wanted) cv_broadcast(&rl->r_wr_cv); if (rl->r_read_wanted) cv_broadcast(&rl->r_rd_cv); mutex_exit(&zp->z_range_lock); } /* * AVL comparison function used to order range locks * Locks are ordered on the start offset of the range. */ int zfs_range_compare(const void *arg1, const void *arg2) { const rl_t *rl1 = arg1; const rl_t *rl2 = arg2; if (rl1->r_off > rl2->r_off) return (1); if (rl1->r_off < rl2->r_off) return (-1); return (0); }