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vfs: Fix sys_sync() and fsync_super() reliability (version 4)

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So far, do_sync() called:
  sync_inodes(0);
  sync_supers();
  sync_filesystems(0);
  sync_filesystems(1);
  sync_inodes(1);

This ordering makes it kind of hard for filesystems as sync_inodes(0) need not
submit all the IO (for example it skips inodes with I_SYNC set) so e.g. forcing
transaction to disk in ->sync_fs() is not really enough. Therefore sys_sync has
not been completely reliable on some filesystems (ext3, ext4, reiserfs, ocfs2
and others are hit by this) when racing e.g. with background writeback. A
similar problem hits also other filesystems (e.g. ext2) because of
write_supers() being called before the sync_inodes(1).

Change the ordering of calls in do_sync() - this requires a new function
sync_blockdevs() to preserve the property that block devices are always synced
after write_super() / sync_fs() call.

The same issue is fixed in __fsync_super() function used on umount /
remount read-only.

[AV: build fixes]

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 16:43:48 +02:00 committed by Al Viro
parent 876a9f76ab
commit 5a3e5cb8e0
3 changed files with 40 additions and 2 deletions
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9
fs/internal.h
View file

@ -71,3 +71,12 @@ 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

29
fs/super.c
View file

@ -293,6 +293,7 @@ void __fsync_super(struct super_block *sb)
{
sync_inodes_sb(sb, 0);
vfs_dq_sync(sb);
sync_inodes_sb(sb, 1);
lock_super(sb);
if (sb->s_dirt && sb->s_op->write_super)
sb->s_op->write_super(sb);
@ -300,7 +301,6 @@ void __fsync_super(struct super_block *sb)
if (sb->s_op->sync_fs)
sb->s_op->sync_fs(sb, 1);
sync_blockdev(sb->s_bdev);
sync_inodes_sb(sb, 1);
}
/*
@ -522,6 +522,33 @@ void sync_filesystems(int wait)
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

4
fs/sync.c
View file

@ -13,6 +13,7 @@
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/buffer_head.h>
#include "internal.h"
#define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \
SYNC_FILE_RANGE_WAIT_AFTER)
@ -26,10 +27,11 @@ 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_inodes(wait); /* Mappings, inodes and blockdevs, again. */
sync_blockdevs();
if (!wait)
printk("Emergency Sync complete\n");
if (unlikely(laptop_mode))