mirror of
https://github.com/torvalds/linux.git
synced 2024-12-08 03:52:16 +00:00
d4a789474a
Signed-off-by: Chris Mason <chris.mason@oracle.com>
235 lines
6.1 KiB
C
235 lines
6.1 KiB
C
/*
|
|
* Copyright (C) 2008 Oracle. All rights reserved.
|
|
*
|
|
* This program is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU General Public
|
|
* License v2 as published by the Free Software Foundation.
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
* General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public
|
|
* License along with this program; if not, write to the
|
|
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
|
|
* Boston, MA 021110-1307, USA.
|
|
*/
|
|
#include <linux/sched.h>
|
|
#include <linux/gfp.h>
|
|
#include <linux/pagemap.h>
|
|
#include <linux/spinlock.h>
|
|
#include <linux/page-flags.h>
|
|
#include <asm/bug.h>
|
|
#include "ctree.h"
|
|
#include "extent_io.h"
|
|
#include "locking.h"
|
|
|
|
static inline void spin_nested(struct extent_buffer *eb)
|
|
{
|
|
spin_lock(&eb->lock);
|
|
}
|
|
|
|
/*
|
|
* Setting a lock to blocking will drop the spinlock and set the
|
|
* flag that forces other procs who want the lock to wait. After
|
|
* this you can safely schedule with the lock held.
|
|
*/
|
|
void btrfs_set_lock_blocking(struct extent_buffer *eb)
|
|
{
|
|
if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) {
|
|
set_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags);
|
|
spin_unlock(&eb->lock);
|
|
}
|
|
/* exit with the spin lock released and the bit set */
|
|
}
|
|
|
|
/*
|
|
* clearing the blocking flag will take the spinlock again.
|
|
* After this you can't safely schedule
|
|
*/
|
|
void btrfs_clear_lock_blocking(struct extent_buffer *eb)
|
|
{
|
|
if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) {
|
|
spin_nested(eb);
|
|
clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags);
|
|
smp_mb__after_clear_bit();
|
|
}
|
|
/* exit with the spin lock held */
|
|
}
|
|
|
|
/*
|
|
* unfortunately, many of the places that currently set a lock to blocking
|
|
* don't end up blocking for very long, and often they don't block
|
|
* at all. For a dbench 50 run, if we don't spin on the blocking bit
|
|
* at all, the context switch rate can jump up to 400,000/sec or more.
|
|
*
|
|
* So, we're still stuck with this crummy spin on the blocking bit,
|
|
* at least until the most common causes of the short blocks
|
|
* can be dealt with.
|
|
*/
|
|
static int btrfs_spin_on_block(struct extent_buffer *eb)
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < 512; i++) {
|
|
if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
|
|
return 1;
|
|
if (need_resched())
|
|
break;
|
|
cpu_relax();
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* This is somewhat different from trylock. It will take the
|
|
* spinlock but if it finds the lock is set to blocking, it will
|
|
* return without the lock held.
|
|
*
|
|
* returns 1 if it was able to take the lock and zero otherwise
|
|
*
|
|
* After this call, scheduling is not safe without first calling
|
|
* btrfs_set_lock_blocking()
|
|
*/
|
|
int btrfs_try_spin_lock(struct extent_buffer *eb)
|
|
{
|
|
int i;
|
|
|
|
if (btrfs_spin_on_block(eb)) {
|
|
spin_nested(eb);
|
|
if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
|
|
return 1;
|
|
spin_unlock(&eb->lock);
|
|
}
|
|
/* spin for a bit on the BLOCKING flag */
|
|
for (i = 0; i < 2; i++) {
|
|
cpu_relax();
|
|
if (!btrfs_spin_on_block(eb))
|
|
break;
|
|
|
|
spin_nested(eb);
|
|
if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
|
|
return 1;
|
|
spin_unlock(&eb->lock);
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* the autoremove wake function will return 0 if it tried to wake up
|
|
* a process that was already awake, which means that process won't
|
|
* count as an exclusive wakeup. The waitq code will continue waking
|
|
* procs until it finds one that was actually sleeping.
|
|
*
|
|
* For btrfs, this isn't quite what we want. We want a single proc
|
|
* to be notified that the lock is ready for taking. If that proc
|
|
* already happen to be awake, great, it will loop around and try for
|
|
* the lock.
|
|
*
|
|
* So, btrfs_wake_function always returns 1, even when the proc that we
|
|
* tried to wake up was already awake.
|
|
*/
|
|
static int btrfs_wake_function(wait_queue_t *wait, unsigned mode,
|
|
int sync, void *key)
|
|
{
|
|
autoremove_wake_function(wait, mode, sync, key);
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* returns with the extent buffer spinlocked.
|
|
*
|
|
* This will spin and/or wait as required to take the lock, and then
|
|
* return with the spinlock held.
|
|
*
|
|
* After this call, scheduling is not safe without first calling
|
|
* btrfs_set_lock_blocking()
|
|
*/
|
|
int btrfs_tree_lock(struct extent_buffer *eb)
|
|
{
|
|
DEFINE_WAIT(wait);
|
|
wait.func = btrfs_wake_function;
|
|
|
|
if (!btrfs_spin_on_block(eb))
|
|
goto sleep;
|
|
|
|
while(1) {
|
|
spin_nested(eb);
|
|
|
|
/* nobody is blocking, exit with the spinlock held */
|
|
if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
|
|
return 0;
|
|
|
|
/*
|
|
* we have the spinlock, but the real owner is blocking.
|
|
* wait for them
|
|
*/
|
|
spin_unlock(&eb->lock);
|
|
|
|
/*
|
|
* spin for a bit, and if the blocking flag goes away,
|
|
* loop around
|
|
*/
|
|
cpu_relax();
|
|
if (btrfs_spin_on_block(eb))
|
|
continue;
|
|
sleep:
|
|
prepare_to_wait_exclusive(&eb->lock_wq, &wait,
|
|
TASK_UNINTERRUPTIBLE);
|
|
|
|
if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
|
|
schedule();
|
|
|
|
finish_wait(&eb->lock_wq, &wait);
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Very quick trylock, this does not spin or schedule. It returns
|
|
* 1 with the spinlock held if it was able to take the lock, or it
|
|
* returns zero if it was unable to take the lock.
|
|
*
|
|
* After this call, scheduling is not safe without first calling
|
|
* btrfs_set_lock_blocking()
|
|
*/
|
|
int btrfs_try_tree_lock(struct extent_buffer *eb)
|
|
{
|
|
if (spin_trylock(&eb->lock)) {
|
|
if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) {
|
|
/*
|
|
* we've got the spinlock, but the real owner is
|
|
* blocking. Drop the spinlock and return failure
|
|
*/
|
|
spin_unlock(&eb->lock);
|
|
return 0;
|
|
}
|
|
return 1;
|
|
}
|
|
/* someone else has the spinlock giveup */
|
|
return 0;
|
|
}
|
|
|
|
int btrfs_tree_unlock(struct extent_buffer *eb)
|
|
{
|
|
/*
|
|
* if we were a blocking owner, we don't have the spinlock held
|
|
* just clear the bit and look for waiters
|
|
*/
|
|
if (test_and_clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
|
|
smp_mb__after_clear_bit();
|
|
else
|
|
spin_unlock(&eb->lock);
|
|
|
|
if (waitqueue_active(&eb->lock_wq))
|
|
wake_up(&eb->lock_wq);
|
|
return 0;
|
|
}
|
|
|
|
void btrfs_assert_tree_locked(struct extent_buffer *eb)
|
|
{
|
|
if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
|
|
assert_spin_locked(&eb->lock);
|
|
}
|