Commit 5a3e5cb8 authored by Jan Kara's avatar Jan Kara Committed by Al Viro
Browse files

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



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: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 876a9f76

fs/internal.h

+9 −0
Original line number Diff line number Diff line
@@ -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

fs/super.c

+28 −1
Original line number Diff line number Diff line
@@ -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 @@ 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

fs/sync.c

+3 −1
Original line number Diff line number Diff line
@@ -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))

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