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vfs: Make sys_sync() use fsync_super() (version 4) 

It is unnecessarily fragile to have two places (fsync_super() and do_sync())
doing data integrity sync of the filesystem. Alter __fsync_super() to
accommodate needs of both callers and use it. So after this patch
__fsync_super() is the only place where we gather all the calls needed to
properly send all data on a filesystem to disk.

Nice bonus is that we get a complete livelock avoidance and write_supers()
is now only used for periodic writeback of superblocks.

sync_blockdevs() introduced a couple of patches ago is gone now.

[build fixes folded]

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jan Kara 2009-04-27 16:43:51 +02:00 committed by Al Viro
parent 429479f031
commit 5cee5815d1
7 changed files with 52 additions and 136 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
fs/block_dev.c
View File

@ -176,17 +176,22 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
iov, offset, nr_segs, blkdev_get_blocks, NULL);
}
int __sync_blockdev(struct block_device *bdev, int wait)
{
if (!bdev)
return 0;
if (!wait)
return filemap_flush(bdev->bd_inode->i_mapping);
return filemap_write_and_wait(bdev->bd_inode->i_mapping);
}
/*
* Write out and wait upon all the dirty data associated with a block
* device via its mapping. Does not take the superblock lock.
*/
int sync_blockdev(struct block_device *bdev)
{
int ret = 0;
if (bdev)
ret = filemap_write_and_wait(bdev->bd_inode->i_mapping);
return ret;
return __sync_blockdev(bdev, 1);
}
EXPORT_SYMBOL(sync_blockdev);

49
fs/fs-writeback.c
View File

@ -678,55 +678,6 @@ void sync_inodes_sb(struct super_block *sb, int wait)
sync_sb_inodes(sb, &wbc);
}
/**
* sync_inodes - writes all inodes to disk
* @wait: wait for completion
*
* sync_inodes() goes through each super block's dirty inode list, writes the
* inodes out, waits on the writeout and puts the inodes back on the normal
* list.
*
* This is for sys_sync(). fsync_dev() uses the same algorithm. The subtle
* part of the sync functions is that the blockdev "superblock" is processed
* last. This is because the write_inode() function of a typical fs will
* perform no I/O, but will mark buffers in the blockdev mapping as dirty.
* What we want to do is to perform all that dirtying first, and then write
* back all those inode blocks via the blockdev mapping in one sweep. So the
* additional (somewhat redundant) sync_blockdev() calls here are to make
* sure that really happens. Because if we call sync_inodes_sb(wait=1) with
* outstanding dirty inodes, the writeback goes block-at-a-time within the
* filesystem's write_inode(). This is extremely slow.
*/
static void __sync_inodes(int wait)
{
struct super_block *sb;
spin_lock(&sb_lock);
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
if (sb->s_root) {
sync_inodes_sb(sb, wait);
sync_blockdev(sb->s_bdev);
}
up_read(&sb->s_umount);
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
}
spin_unlock(&sb_lock);
}
void sync_inodes(int wait)
{
__sync_inodes(0);
if (wait)
__sync_inodes(1);
}
/**
* write_inode_now - write an inode to disk
* @inode: inode to write to disk

16
fs/internal.h
View File

@ -25,6 +25,8 @@ static inline int sb_is_blkdev_sb(struct super_block *sb)
return sb == blockdev_superblock;
}
extern int __sync_blockdev(struct block_device *bdev, int wait);
#else
static inline void bdev_cache_init(void)
{
@ -34,6 +36,11 @@ static inline int sb_is_blkdev_sb(struct super_block *sb)
{
return 0;
}
static inline int __sync_blockdev(struct block_device *bdev, int wait)
{
return 0;
}
#endif
/*
@ -71,12 +78,3 @@ extern void chroot_fs_refs(struct path *, struct path *);
* file_table.c
*/
extern void mark_files_ro(struct super_block *);
/*
* super.c
*/
#ifdef CONFIG_BLOCK
extern void sync_blockdevs(void);
#else
static inline void sync_blockdevs(void) { }
#endif

72
fs/super.c
View File

@ -284,23 +284,23 @@ EXPORT_SYMBOL(lock_super);
EXPORT_SYMBOL(unlock_super);
/*
* Write out and wait upon all dirty data associated with this
* superblock. Filesystem data as well as the underlying block
* device. Takes the superblock lock. Requires a second blkdev
* flush by the caller to complete the operation.
* Do the filesystem syncing work. For simple filesystems sync_inodes_sb(sb, 0)
* just dirties buffers with inodes so we have to submit IO for these buffers
* via __sync_blockdev(). This also speeds up the wait == 1 case since in that
* case write_inode() functions do sync_dirty_buffer() and thus effectively
* write one block at a time.
*/
static int __fsync_super(struct super_block *sb)
static int __fsync_super(struct super_block *sb, int wait)
{
sync_inodes_sb(sb, 0);
vfs_dq_sync(sb);
sync_inodes_sb(sb, 1);
sync_inodes_sb(sb, wait);
lock_super(sb);
if (sb->s_dirt && sb->s_op->write_super)
sb->s_op->write_super(sb);
unlock_super(sb);
if (sb->s_op->sync_fs)
sb->s_op->sync_fs(sb, 1);
return sync_blockdev(sb->s_bdev);
sb->s_op->sync_fs(sb, wait);
return __sync_blockdev(sb->s_bdev, wait);
}
/*
@ -310,7 +310,12 @@ static int __fsync_super(struct super_block *sb)
*/
int fsync_super(struct super_block *sb)
{
return __fsync_super(sb);
int ret;
ret = __fsync_super(sb, 0);
if (ret < 0)
return ret;
return __fsync_super(sb, 1);
}
EXPORT_SYMBOL_GPL(fsync_super);
@ -469,20 +474,18 @@ restart:
}
/*
* Call the ->sync_fs super_op against all filesystems which are r/w and
* which implement it.
* 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_fs
* 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_fs
* 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.
*
* (Fabian) Avoid sync_fs with clean fs & wait mode 0
*/
void sync_filesystems(int wait)
{
@ -492,25 +495,23 @@ void sync_filesystems(int wait)
mutex_lock(&mutex); /* Could be down_interruptible */
spin_lock(&sb_lock);
list_for_each_entry(sb, &super_blocks, s_list) {
if (!sb->s_op->sync_fs)
continue;
if (sb->s_flags & MS_RDONLY)
continue;
sb->s_need_sync_fs = 1;
sb->s_need_sync = 1;
}
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
if (!sb->s_need_sync_fs)
if (!sb->s_need_sync)
continue;
sb->s_need_sync_fs = 0;
sb->s_need_sync = 0;
if (sb->s_flags & MS_RDONLY)
continue; /* hm. Was remounted r/o meanwhile */
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
if (sb->s_root)
sb->s_op->sync_fs(sb, wait);
__fsync_super(sb, wait);
up_read(&sb->s_umount);
/* restart only when sb is no longer on the list */
spin_lock(&sb_lock);
@ -521,33 +522,6 @@ restart:
mutex_unlock(&mutex);
}
#ifdef CONFIG_BLOCK
/*
* Sync all block devices underlying some superblock
*/
void sync_blockdevs(void)
{
struct super_block *sb;
spin_lock(&sb_lock);
restart:
list_for_each_entry(sb, &super_blocks, s_list) {
if (!sb->s_bdev)
continue;
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
if (sb->s_root)
sync_blockdev(sb->s_bdev);
up_read(&sb->s_umount);
spin_lock(&sb_lock);
if (__put_super_and_need_restart(sb))
goto restart;
}
spin_unlock(&sb_lock);
}
#endif
/**
* get_super - get the superblock of a device
* @bdev: device to get the superblock for

33
fs/sync.c
View File

@ -18,35 +18,24 @@
#define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \
SYNC_FILE_RANGE_WAIT_AFTER)
/*
* sync everything. Start out by waking pdflush, because that writes back
* all queues in parallel.
*/
static void do_sync(unsigned long wait)
{
wakeup_pdflush(0);
sync_inodes(0); /* All mappings, inodes and their blockdevs */
vfs_dq_sync(NULL);
sync_inodes(wait); /* Mappings, inodes and blockdevs, again. */
sync_supers(); /* Write the superblocks */
sync_filesystems(0); /* Start syncing the filesystems */
sync_filesystems(wait); /* Waitingly sync the filesystems */
sync_blockdevs();
if (!wait)
printk("Emergency Sync complete\n");
if (unlikely(laptop_mode))
laptop_sync_completion();
}
SYSCALL_DEFINE0(sync)
{
do_sync(1);
sync_filesystems(0);
sync_filesystems(1);
if (unlikely(laptop_mode))
laptop_sync_completion();
return 0;
}
static void do_sync_work(struct work_struct *work)
{
do_sync(0);
/*
* Sync twice to reduce the possibility we skipped some inodes / pages
* because they were temporarily locked
*/
sync_filesystems(0);
sync_filesystems(0);
printk("Emergency Sync complete\n");
kfree(work);
}

2
include/linux/fs.h
View File

@ -1321,7 +1321,7 @@ struct super_block {
struct rw_semaphore s_umount;
struct mutex s_lock;
int s_count;
int s_need_sync_fs;
int s_need_sync;
atomic_t s_active;
#ifdef CONFIG_SECURITY
void *s_security;

1
include/linux/writeback.h
View File

@ -79,7 +79,6 @@ struct writeback_control {
void writeback_inodes(struct writeback_control *wbc);
int inode_wait(void *);
void sync_inodes_sb(struct super_block *, int wait);
void sync_inodes(int wait);
/* writeback.h requires fs.h; it, too, is not included from here. */
static inline void wait_on_inode(struct inode *inode)