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get rid of restarts in sync_filesystems() 

At the same time we can kill s_need_restart and local mutex in there.
__put_super() made public for a while; will be gone later.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2010-03-22 19:56:42 -04:00
parent 551de6f34d
commit 8edd64bd60
3 changed files with 5 additions and 27 deletions
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2
fs/super.c
View File

@ -130,7 +130,7 @@ static inline void destroy_super(struct super_block *s)
* Drop a superblock's refcount. Returns non-zero if the superblock was
* destroyed. The caller must hold sb_lock.
*/
static int __put_super(struct super_block *sb)
int __put_super(struct super_block *sb)
{
int ret = 0;

28
fs/sync.c
View File

@ -80,35 +80,15 @@ EXPORT_SYMBOL_GPL(sync_filesystem);
/*
* Sync all the data for all the filesystems (called by sys_sync() and
* emergency sync)
*
* This operation is careful to avoid the livelock which could easily happen
* if two or more filesystems are being continuously dirtied. s_need_sync
* is used only here. We set it against all filesystems and then clear it as
* we sync them. So redirtied filesystems are skipped.
*
* But if process A is currently running sync_filesystems and then process B
* calls sync_filesystems as well, process B will set all the s_need_sync
* flags again, which will cause process A to resync everything. Fix that with
* a local mutex.
*/
static void sync_filesystems(int wait)
{
struct super_block *sb;
static DEFINE_MUTEX(mutex);
struct super_block *sb, *n;
mutex_lock(&mutex); /* Could be down_interruptible */
spin_lock(&sb_lock);
list_for_each_entry(sb, &super_blocks, s_list)
if (!list_empty(&sb->s_instances))
sb->s_need_sync = 1;
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
list_for_each_entry_safe(sb, n, &super_blocks, s_list) {
if (list_empty(&sb->s_instances))
continue;
if (!sb->s_need_sync)
continue;
sb->s_need_sync = 0;
sb->s_count++;
spin_unlock(&sb_lock);
@ -119,11 +99,9 @@ restart:
/* restart only when sb is no longer on the list */
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
__put_super(sb);
}
spin_unlock(&sb_lock);
mutex_unlock(&mutex);
}
/*

2
include/linux/fs.h
View File

@ -1332,7 +1332,6 @@ struct super_block {
struct rw_semaphore s_umount;
struct mutex s_lock;
int s_count;
int s_need_sync;
atomic_t s_active;
#ifdef CONFIG_SECURITY
void *s_security;
@ -1780,6 +1779,7 @@ extern int get_sb_pseudo(struct file_system_type *, char *,
struct vfsmount *mnt);
extern void simple_set_mnt(struct vfsmount *mnt, struct super_block *sb);
int __put_super_and_need_restart(struct super_block *sb);
int __put_super(struct super_block *sb);
void put_super(struct super_block *sb);
/* Alas, no aliases. Too much hassle with bringing module.h everywhere */