drivers/staging/lustre/lustre/llite/range_lock.c

   1 /*
   2  * GPL HEADER START
   3  *
   4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 only,
   8  * as published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * General Public License version 2 for more details (a copy is included
  14  * in the LICENSE file that accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * version 2 along with this program; If not, see
  18  * http://www.gnu.org/licenses/gpl-2.0.html
  19  *
  20  * GPL HEADER END
  21  */
  22 /*
  23  * Range lock is used to allow multiple threads writing a single shared
  24  * file given each thread is writing to a non-overlapping portion of the
  25  * file.
  26  *
  27  * Refer to the possible upstream kernel version of range lock by
  28  * Jan Kara <jack@suse.cz>: https://lkml.org/lkml/2013/1/31/480
  29  *
  30  * This file could later replaced by the upstream kernel version.
  31  */
  32 /*
  33  * Author: Prakash Surya <surya1@llnl.gov>
  34  * Author: Bobi Jam <bobijam.xu@intel.com>
  35  */
  36 #include "range_lock.h"
  37 #include "../include/lustre/lustre_user.h"
  38
  39 /**
  40  * Initialize a range lock tree
  41  *
  42  * \param tree [in]     an empty range lock tree
  43  *
  44  * Pre:  Caller should have allocated the range lock tree.
  45  * Post: The range lock tree is ready to function.
  46  */
  47 void range_lock_tree_init(struct range_lock_tree *tree)
  48 {
  49         tree->rlt_root = NULL;
  50         tree->rlt_sequence = 0;
  51         spin_lock_init(&tree->rlt_lock);
  52 }
  53
  54 /**
  55  * Initialize a range lock node
  56  *
  57  * \param lock  [in]    an empty range lock node
  58  * \param start [in]    start of the covering region
  59  * \param end   [in]    end of the covering region
  60  *
  61  * Pre:  Caller should have allocated the range lock node.
  62  * Post: The range lock node is meant to cover [start, end] region
  63  */
  64 void range_lock_init(struct range_lock *lock, __u64 start, __u64 end)
  65 {
  66         memset(&lock->rl_node, 0, sizeof(lock->rl_node));
  67         if (end != LUSTRE_EOF)
  68                 end >>= PAGE_SHIFT;
  69         interval_set(&lock->rl_node, start >> PAGE_SHIFT, end);
  70         INIT_LIST_HEAD(&lock->rl_next_lock);
  71         lock->rl_task = NULL;
  72         lock->rl_lock_count = 0;
  73         lock->rl_blocking_ranges = 0;
  74         lock->rl_sequence = 0;
  75 }
  76
  77 static inline struct range_lock *next_lock(struct range_lock *lock)
  78 {
  79         return list_entry(lock->rl_next_lock.next, typeof(*lock), rl_next_lock);
  80 }
  81
  82 /**
  83  * Helper function of range_unlock()
  84  *
  85  * \param node [in]     a range lock found overlapped during interval node
  86  *                      search
  87  * \param arg [in]      the range lock to be tested
  88  *
  89  * \retval INTERVAL_ITER_CONT   indicate to continue the search for next
  90  *                              overlapping range node
  91  * \retval INTERVAL_ITER_STOP   indicate to stop the search
  92  */
  93 static enum interval_iter range_unlock_cb(struct interval_node *node, void *arg)
  94 {
  95         struct range_lock *lock = arg;
  96         struct range_lock *overlap = node2rangelock(node);
  97         struct range_lock *iter;
  98
  99         list_for_each_entry(iter, &overlap->rl_next_lock, rl_next_lock) {
 100                 if (iter->rl_sequence > lock->rl_sequence) {
 101                         --iter->rl_blocking_ranges;
 102                         LASSERT(iter->rl_blocking_ranges > 0);
 103                 }
 104         }
 105         if (overlap->rl_sequence > lock->rl_sequence) {
 106                 --overlap->rl_blocking_ranges;
 107                 if (overlap->rl_blocking_ranges == 0)
 108                         wake_up_process(overlap->rl_task);
 109         }
 110         return INTERVAL_ITER_CONT;
 111 }
 112
 113 /**
 114  * Unlock a range lock, wake up locks blocked by this lock.
 115  *
 116  * \param tree [in]     range lock tree
 117  * \param lock [in]     range lock to be deleted
 118  *
 119  * If this lock has been granted, relase it; if not, just delete it from
 120  * the tree or the same region lock list. Wake up those locks only blocked
 121  * by this lock through range_unlock_cb().
 122  */
 123 void range_unlock(struct range_lock_tree *tree, struct range_lock *lock)
 124 {
 125         spin_lock(&tree->rlt_lock);
 126         if (!list_empty(&lock->rl_next_lock)) {
 127                 struct range_lock *next;
 128
 129                 if (interval_is_intree(&lock->rl_node)) { /* first lock */
 130                         /* Insert the next same range lock into the tree */
 131                         next = next_lock(lock);
 132                         next->rl_lock_count = lock->rl_lock_count - 1;
 133                         interval_erase(&lock->rl_node, &tree->rlt_root);
 134                         interval_insert(&next->rl_node, &tree->rlt_root);
 135                 } else {
 136                         /* find the first lock in tree */
 137                         list_for_each_entry(next, &lock->rl_next_lock,
 138                                             rl_next_lock) {
 139                                 if (!interval_is_intree(&next->rl_node))
 140                                         continue;
 141
 142                                 LASSERT(next->rl_lock_count > 0);
 143                                 next->rl_lock_count--;
 144                                 break;
 145                         }
 146                 }
 147                 list_del_init(&lock->rl_next_lock);
 148         } else {
 149                 LASSERT(interval_is_intree(&lock->rl_node));
 150                 interval_erase(&lock->rl_node, &tree->rlt_root);
 151         }
 152
 153         interval_search(tree->rlt_root, &lock->rl_node.in_extent,
 154                         range_unlock_cb, lock);
 155         spin_unlock(&tree->rlt_lock);
 156 }
 157
 158 /**
 159  * Helper function of range_lock()
 160  *
 161  * \param node [in]     a range lock found overlapped during interval node
 162  *                      search
 163  * \param arg [in]      the range lock to be tested
 164  *
 165  * \retval INTERVAL_ITER_CONT   indicate to continue the search for next
 166  *                              overlapping range node
 167  * \retval INTERVAL_ITER_STOP   indicate to stop the search
 168  */
 169 static enum interval_iter range_lock_cb(struct interval_node *node, void *arg)
 170 {
 171         struct range_lock *lock = (struct range_lock *)arg;
 172         struct range_lock *overlap = node2rangelock(node);
 173
 174         lock->rl_blocking_ranges += overlap->rl_lock_count + 1;
 175         return INTERVAL_ITER_CONT;
 176 }
 177
 178 /**
 179  * Lock a region
 180  *
 181  * \param tree [in]     range lock tree
 182  * \param lock [in]     range lock node containing the region span
 183  *
 184  * \retval 0    get the range lock
 185  * \retval <0   error code while not getting the range lock
 186  *
 187  * If there exists overlapping range lock, the new lock will wait and
 188  * retry, if later it find that it is not the chosen one to wake up,
 189  * it wait again.
 190  */
 191 int range_lock(struct range_lock_tree *tree, struct range_lock *lock)
 192 {
 193         struct interval_node *node;
 194         int rc = 0;
 195
 196         spin_lock(&tree->rlt_lock);
 197         /*
 198          * We need to check for all conflicting intervals
 199          * already in the tree.
 200          */
 201         interval_search(tree->rlt_root, &lock->rl_node.in_extent,
 202                         range_lock_cb, lock);
 203         /*
 204          * Insert to the tree if I am unique, otherwise I've been linked to
 205          * the rl_next_lock of another lock which has the same range as mine
 206          * in range_lock_cb().
 207          */
 208         node = interval_insert(&lock->rl_node, &tree->rlt_root);
 209         if (node) {
 210                 struct range_lock *tmp = node2rangelock(node);
 211
 212                 list_add_tail(&lock->rl_next_lock, &tmp->rl_next_lock);
 213                 tmp->rl_lock_count++;
 214         }
 215         lock->rl_sequence = ++tree->rlt_sequence;
 216
 217         while (lock->rl_blocking_ranges > 0) {
 218                 lock->rl_task = current;
 219                 __set_current_state(TASK_INTERRUPTIBLE);
 220                 spin_unlock(&tree->rlt_lock);
 221                 schedule();
 222
 223                 if (signal_pending(current)) {
 224                         range_unlock(tree, lock);
 225                         rc = -EINTR;
 226                         goto out;
 227                 }
 228                 spin_lock(&tree->rlt_lock);
 229         }
 230         spin_unlock(&tree->rlt_lock);
 231 out:
 232         return rc;
 233 }