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Message-Id: <1240415781-17834-3-git-send-email-jack@suse.cz>
Date: Wed, 22 Apr 2009 17:56:21 +0200
From: Jan Kara <jack@...e.cz>
To: LKML <linux-kernel@...r.kernel.org>
Cc: linux-fsdevel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Jens Axboe <jens.axboe@...cle.com>, Jan Kara <jack@...e.cz>
Subject: [PATCH] vfs: Merge sync_supers(), sync_filesystems() and sync_blockdevs()
These three functions are quite similar so merge them to save superblock list
traversal code. As a bonus we get livelock avoidance for all these superblock
traversals. Also remove the condition that if wait == 0 and sb->s_dirt is
not set, then ->sync_fs() is not called. This does not really make much sence
since s_dirt is generally used by filesystem to mean that ->write_super() needs
to be called. But ->sync_fs() does different things. I even suspect that some
filesystems (btrfs?) sets s_dirt just to fool this logic.
Signed-off-by: Jan Kara <jack@...e.cz>
---
fs/super.c | 104 ++++++++++++++------------------------------------
fs/sync.c | 12 ++++--
include/linux/fs.h | 11 +++--
mm/page-writeback.c | 2 +-
4 files changed, 44 insertions(+), 85 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index 4f56333..6d6209e 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -413,58 +413,24 @@ void drop_super(struct super_block *sb)
EXPORT_SYMBOL(drop_super);
-static inline void write_super(struct super_block *sb)
-{
- lock_super(sb);
- if (sb->s_root && sb->s_dirt)
- if (sb->s_op->write_super)
- sb->s_op->write_super(sb);
- unlock_super(sb);
-}
-
-/*
- * Note: check the dirty flag before waiting, so we don't
- * hold up the sync while mounting a device. (The newly
- * mounted device won't need syncing.)
- */
-void sync_supers(void)
-{
- struct super_block *sb;
-
- spin_lock(&sb_lock);
-restart:
- list_for_each_entry(sb, &super_blocks, s_list) {
- if (sb->s_dirt) {
- sb->s_count++;
- spin_unlock(&sb_lock);
- down_read(&sb->s_umount);
- write_super(sb);
- up_read(&sb->s_umount);
- spin_lock(&sb_lock);
- if (__put_super_and_need_restart(sb))
- goto restart;
- }
- }
- spin_unlock(&sb_lock);
-}
-
/*
- * Call the ->sync_fs super_op against all filesystems which are r/w and
- * which implement it.
+ * Call the ->write_super, ->sync_fs, sync_blockdev() against all filesystems
+ * which are r/w and which implement it.
*
- * 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
- * is used only here. We set it against all filesystems and then clear it as
- * we sync them. So redirtied filesystems are skipped.
+ * This operation is careful to avoid the livelock. Currently it's not so easy
+ * to trigger as it used to be - we restart scanning the superblock list only
+ * if the superblock got unmounted under us - but it's better to be safe and it
+ * doesn't cost us much. 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
- * flags again, which will cause process A to resync everything. Fix that with
- * a local mutex.
+ * 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)
+void sync_filesystems(int what, int wait)
{
struct super_block *sb;
static DEFINE_MUTEX(mutex);
@@ -472,26 +438,37 @@ 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)
+ if ((!sb->s_op->sync_fs || !(what & FSSYNC_FS)) &&
+ (!sb->s_op->write_super || !(what & FSSYNC_SUPER)) &&
+ !(what & FSSYNC_BDEV))
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);
async_synchronize_full_domain(&sb->s_async_list);
- if (sb->s_root && (wait || sb->s_dirt))
- sb->s_op->sync_fs(sb, wait);
+ if (sb->s_root) {
+ lock_super(sb);
+ if (what & FSSYNC_SUPER && sb->s_dirt &&
+ sb->s_op->write_super)
+ sb->s_op->write_super(sb);
+ unlock_super(sb);
+ if (what & FSSYNC_FS && sb->s_op->sync_fs)
+ sb->s_op->sync_fs(sb, wait);
+ if (what & FSSYNC_BDEV)
+ sync_blockdev(sb->s_bdev);
+ }
up_read(&sb->s_umount);
/* restart only when sb is no longer on the list */
spin_lock(&sb_lock);
@@ -502,29 +479,6 @@ restart:
mutex_unlock(&mutex);
}
-/*
- * 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) {
- 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);
-}
-
/**
* 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 fa14e42..3c677ee 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -26,11 +26,15 @@ static void do_sync(unsigned long wait)
wakeup_pdflush(0);
sync_inodes(0); /* All mappings, inodes and their blockdevs */
vfs_dq_sync(NULL);
+ sync_filesystems(FSSYNC_FS, 0); /* Start syncing the filesystems */
+ /*
+ * We have to reliably submit IO for all the inodes before writing
+ * super blocks and calling sync_fs(). Otherwise superblock could miss
+ * some updates or journal could still have uncommitted data.
+ */
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();
+ /* Waitingly sync the filesystems */
+ sync_filesystems(FSSYNC_SUPER | FSSYNC_FS | FSSYNC_BDEV, wait);
if (!wait)
printk("Emergency Sync complete\n");
if (unlikely(laptop_mode))
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4bad02e..2758e75 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -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;
@@ -1942,7 +1942,6 @@ extern void bdput(struct block_device *);
extern struct block_device *open_by_devnum(dev_t, fmode_t);
extern void invalidate_bdev(struct block_device *);
extern int sync_blockdev(struct block_device *bdev);
-extern void sync_blockdevs(void);
extern struct super_block *freeze_bdev(struct block_device *);
extern void emergency_thaw_all(void);
extern int thaw_bdev(struct block_device *bdev, struct super_block *sb);
@@ -1952,7 +1951,6 @@ extern int fsync_no_super(struct block_device *);
#else
static inline void bd_forget(struct inode *inode) {}
static inline int sync_blockdev(struct block_device *bdev) { return 0; }
-static inline void sync_blockdevs(void) { }
static inline void invalidate_bdev(struct block_device *bdev) {}
static inline struct super_block *freeze_bdev(struct block_device *sb)
@@ -2082,8 +2080,11 @@ extern int filemap_fdatawrite_range(struct address_space *mapping,
loff_t start, loff_t end);
extern int vfs_fsync(struct file *file, struct dentry *dentry, int datasync);
-extern void sync_supers(void);
-extern void sync_filesystems(int wait);
+/* Flags telling what should be synced by sync_filesystems() */
+#define FSSYNC_FS 1
+#define FSSYNC_SUPER 2
+#define FSSYNC_BDEV 4
+extern void sync_filesystems(int what, int wait);
extern void __fsync_super(struct super_block *sb);
extern void emergency_sync(void);
extern void emergency_remount(void);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 30351f0..05a2948 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -768,7 +768,7 @@ static void wb_kupdate(unsigned long arg)
.range_cyclic = 1,
};
- sync_supers();
+ sync_filesystems(FSSYNC_SUPER, 0);
oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval);
start_jif = jiffies;
--
1.6.0.2
--
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