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: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/internal.h b/fs/internal.h
index 6d4ef20..343a537 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -71,3 +71,12 @@
* 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
diff --git a/fs/super.c b/fs/super.c
index 3d9f117..18d159d 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -293,6 +293,7 @@
{
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 @@
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 @@
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
diff --git a/fs/sync.c b/fs/sync.c
index 7abc65f..631fd5a 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -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 @@
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))