Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2008 Oracle. All rights reserved. |
| 3 | * |
| 4 | * This program is free software; you can redistribute it and/or |
| 5 | * modify it under the terms of the GNU General Public |
| 6 | * License v2 as published by the Free Software Foundation. |
| 7 | * |
| 8 | * This program is distributed in the hope that it will be useful, |
| 9 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 10 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 11 | * General Public License for more details. |
| 12 | * |
| 13 | * You should have received a copy of the GNU General Public |
| 14 | * License along with this program; if not, write to the |
| 15 | * Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
| 16 | * Boston, MA 021110-1307, USA. |
| 17 | */ |
| 18 | #include <linux/sched.h> |
| 19 | #include <linux/gfp.h> |
| 20 | #include <linux/pagemap.h> |
| 21 | #include <linux/spinlock.h> |
| 22 | #include <linux/page-flags.h> |
Chris Mason | 4881ee5 | 2008-07-24 09:51:08 -0400 | [diff] [blame] | 23 | #include <asm/bug.h> |
Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 24 | #include "ctree.h" |
| 25 | #include "extent_io.h" |
| 26 | #include "locking.h" |
| 27 | |
Chris Mason | b4ce94d | 2009-02-04 09:25:08 -0500 | [diff] [blame] | 28 | static inline void spin_nested(struct extent_buffer *eb) |
| 29 | { |
| 30 | spin_lock(&eb->lock); |
| 31 | } |
Chris Mason | d397712 | 2009-01-05 21:25:51 -0500 | [diff] [blame] | 32 | |
Chris Mason | b4ce94d | 2009-02-04 09:25:08 -0500 | [diff] [blame] | 33 | /* |
| 34 | * Setting a lock to blocking will drop the spinlock and set the |
| 35 | * flag that forces other procs who want the lock to wait. After |
| 36 | * this you can safely schedule with the lock held. |
| 37 | */ |
| 38 | void btrfs_set_lock_blocking(struct extent_buffer *eb) |
| 39 | { |
| 40 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) { |
| 41 | set_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags); |
| 42 | spin_unlock(&eb->lock); |
| 43 | } |
| 44 | /* exit with the spin lock released and the bit set */ |
| 45 | } |
| 46 | |
| 47 | /* |
| 48 | * clearing the blocking flag will take the spinlock again. |
| 49 | * After this you can't safely schedule |
| 50 | */ |
| 51 | void btrfs_clear_lock_blocking(struct extent_buffer *eb) |
| 52 | { |
| 53 | if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) { |
| 54 | spin_nested(eb); |
| 55 | clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags); |
| 56 | smp_mb__after_clear_bit(); |
| 57 | } |
| 58 | /* exit with the spin lock held */ |
| 59 | } |
| 60 | |
| 61 | /* |
| 62 | * unfortunately, many of the places that currently set a lock to blocking |
| 63 | * don't end up blocking for every long, and often they don't block |
| 64 | * at all. For a dbench 50 run, if we don't spin one the blocking bit |
| 65 | * at all, the context switch rate can jump up to 400,000/sec or more. |
| 66 | * |
| 67 | * So, we're still stuck with this crummy spin on the blocking bit, |
| 68 | * at least until the most common causes of the short blocks |
| 69 | * can be dealt with. |
| 70 | */ |
| 71 | static int btrfs_spin_on_block(struct extent_buffer *eb) |
Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 72 | { |
Chris Mason | f9efa9c | 2008-06-25 16:14:04 -0400 | [diff] [blame] | 73 | int i; |
Chris Mason | f9efa9c | 2008-06-25 16:14:04 -0400 | [diff] [blame] | 74 | for (i = 0; i < 512; i++) { |
| 75 | cpu_relax(); |
Chris Mason | b4ce94d | 2009-02-04 09:25:08 -0500 | [diff] [blame] | 76 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) |
| 77 | return 1; |
| 78 | if (need_resched()) |
| 79 | break; |
Chris Mason | f9efa9c | 2008-06-25 16:14:04 -0400 | [diff] [blame] | 80 | } |
Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 81 | return 0; |
| 82 | } |
| 83 | |
Chris Mason | b4ce94d | 2009-02-04 09:25:08 -0500 | [diff] [blame] | 84 | /* |
| 85 | * This is somewhat different from trylock. It will take the |
| 86 | * spinlock but if it finds the lock is set to blocking, it will |
| 87 | * return without the lock held. |
| 88 | * |
| 89 | * returns 1 if it was able to take the lock and zero otherwise |
| 90 | * |
| 91 | * After this call, scheduling is not safe without first calling |
| 92 | * btrfs_set_lock_blocking() |
| 93 | */ |
| 94 | int btrfs_try_spin_lock(struct extent_buffer *eb) |
| 95 | { |
| 96 | int i; |
| 97 | |
| 98 | spin_nested(eb); |
| 99 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) |
| 100 | return 1; |
| 101 | spin_unlock(&eb->lock); |
| 102 | |
| 103 | /* spin for a bit on the BLOCKING flag */ |
| 104 | for (i = 0; i < 2; i++) { |
| 105 | if (!btrfs_spin_on_block(eb)) |
| 106 | break; |
| 107 | |
| 108 | spin_nested(eb); |
| 109 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) |
| 110 | return 1; |
| 111 | spin_unlock(&eb->lock); |
| 112 | } |
| 113 | return 0; |
| 114 | } |
| 115 | |
| 116 | /* |
| 117 | * the autoremove wake function will return 0 if it tried to wake up |
| 118 | * a process that was already awake, which means that process won't |
| 119 | * count as an exclusive wakeup. The waitq code will continue waking |
| 120 | * procs until it finds one that was actually sleeping. |
| 121 | * |
| 122 | * For btrfs, this isn't quite what we want. We want a single proc |
| 123 | * to be notified that the lock is ready for taking. If that proc |
| 124 | * already happen to be awake, great, it will loop around and try for |
| 125 | * the lock. |
| 126 | * |
| 127 | * So, btrfs_wake_function always returns 1, even when the proc that we |
| 128 | * tried to wake up was already awake. |
| 129 | */ |
| 130 | static int btrfs_wake_function(wait_queue_t *wait, unsigned mode, |
| 131 | int sync, void *key) |
| 132 | { |
| 133 | autoremove_wake_function(wait, mode, sync, key); |
| 134 | return 1; |
| 135 | } |
| 136 | |
| 137 | /* |
| 138 | * returns with the extent buffer spinlocked. |
| 139 | * |
| 140 | * This will spin and/or wait as required to take the lock, and then |
| 141 | * return with the spinlock held. |
| 142 | * |
| 143 | * After this call, scheduling is not safe without first calling |
| 144 | * btrfs_set_lock_blocking() |
| 145 | */ |
| 146 | int btrfs_tree_lock(struct extent_buffer *eb) |
| 147 | { |
| 148 | DEFINE_WAIT(wait); |
| 149 | wait.func = btrfs_wake_function; |
| 150 | |
| 151 | while(1) { |
| 152 | spin_nested(eb); |
| 153 | |
| 154 | /* nobody is blocking, exit with the spinlock held */ |
| 155 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) |
| 156 | return 0; |
| 157 | |
| 158 | /* |
| 159 | * we have the spinlock, but the real owner is blocking. |
| 160 | * wait for them |
| 161 | */ |
| 162 | spin_unlock(&eb->lock); |
| 163 | |
| 164 | /* |
| 165 | * spin for a bit, and if the blocking flag goes away, |
| 166 | * loop around |
| 167 | */ |
| 168 | if (btrfs_spin_on_block(eb)) |
| 169 | continue; |
| 170 | |
| 171 | prepare_to_wait_exclusive(&eb->lock_wq, &wait, |
| 172 | TASK_UNINTERRUPTIBLE); |
| 173 | |
| 174 | if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) |
| 175 | schedule(); |
| 176 | |
| 177 | finish_wait(&eb->lock_wq, &wait); |
| 178 | } |
| 179 | return 0; |
| 180 | } |
| 181 | |
| 182 | /* |
| 183 | * Very quick trylock, this does not spin or schedule. It returns |
| 184 | * 1 with the spinlock held if it was able to take the lock, or it |
| 185 | * returns zero if it was unable to take the lock. |
| 186 | * |
| 187 | * After this call, scheduling is not safe without first calling |
| 188 | * btrfs_set_lock_blocking() |
| 189 | */ |
Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 190 | int btrfs_try_tree_lock(struct extent_buffer *eb) |
| 191 | { |
Chris Mason | b4ce94d | 2009-02-04 09:25:08 -0500 | [diff] [blame] | 192 | if (spin_trylock(&eb->lock)) { |
| 193 | if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) { |
| 194 | /* |
| 195 | * we've got the spinlock, but the real owner is |
| 196 | * blocking. Drop the spinlock and return failure |
| 197 | */ |
| 198 | spin_unlock(&eb->lock); |
| 199 | return 0; |
| 200 | } |
| 201 | return 1; |
| 202 | } |
| 203 | /* someone else has the spinlock giveup */ |
| 204 | return 0; |
Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 205 | } |
| 206 | |
| 207 | int btrfs_tree_unlock(struct extent_buffer *eb) |
| 208 | { |
Chris Mason | b4ce94d | 2009-02-04 09:25:08 -0500 | [diff] [blame] | 209 | /* |
| 210 | * if we were a blocking owner, we don't have the spinlock held |
| 211 | * just clear the bit and look for waiters |
| 212 | */ |
| 213 | if (test_and_clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) |
| 214 | smp_mb__after_clear_bit(); |
| 215 | else |
| 216 | spin_unlock(&eb->lock); |
| 217 | |
| 218 | if (waitqueue_active(&eb->lock_wq)) |
| 219 | wake_up(&eb->lock_wq); |
Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 220 | return 0; |
| 221 | } |
| 222 | |
Chris Mason | b9447ef8 | 2009-03-09 11:45:38 -0400 | [diff] [blame] | 223 | void btrfs_assert_tree_locked(struct extent_buffer *eb) |
Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 224 | { |
Chris Mason | b9447ef8 | 2009-03-09 11:45:38 -0400 | [diff] [blame] | 225 | if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) |
| 226 | assert_spin_locked(&eb->lock); |
Chris Mason | 925baed | 2008-06-25 16:01:30 -0400 | [diff] [blame] | 227 | } |