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yaml
---
r: 320983
b: refs/heads/master
c: 5accdf8
h: refs/heads/master
i:
  320981: 09c167d
  320979: 06171bd
  320975: 6c5db1e
v: v3
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Jan Kara authored and Al Viro committed Jul 31, 2012
1 parent 57a2a83 commit ad2be68
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Showing 3 changed files with 374 additions and 29 deletions.
2 changes: 1 addition & 1 deletion [refs]
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Original file line number Diff line number Diff line change
@@ -1,2 +1,2 @@
---
refs/heads/master: d87aae2f3c8e90bd0fe03f5309b4d066b712b8ec
refs/heads/master: 5accdf82ba25cacefd6c1867f1704beb4d244cdd
251 changes: 230 additions & 21 deletions trunk/fs/super.c
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Original file line number Diff line number Diff line change
Expand Up @@ -33,12 +33,19 @@
#include <linux/rculist_bl.h>
#include <linux/cleancache.h>
#include <linux/fsnotify.h>
#include <linux/lockdep.h>
#include "internal.h"


LIST_HEAD(super_blocks);
DEFINE_SPINLOCK(sb_lock);

static char *sb_writers_name[SB_FREEZE_LEVELS] = {
"sb_writers",
"sb_pagefaults",
"sb_internal",
};

/*
* One thing we have to be careful of with a per-sb shrinker is that we don't
* drop the last active reference to the superblock from within the shrinker.
Expand Down Expand Up @@ -102,6 +109,35 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
return total_objects;
}

static int init_sb_writers(struct super_block *s, struct file_system_type *type)
{
int err;
int i;

for (i = 0; i < SB_FREEZE_LEVELS; i++) {
err = percpu_counter_init(&s->s_writers.counter[i], 0);
if (err < 0)
goto err_out;
lockdep_init_map(&s->s_writers.lock_map[i], sb_writers_name[i],
&type->s_writers_key[i], 0);
}
init_waitqueue_head(&s->s_writers.wait);
init_waitqueue_head(&s->s_writers.wait_unfrozen);
return 0;
err_out:
while (--i >= 0)
percpu_counter_destroy(&s->s_writers.counter[i]);
return err;
}

static void destroy_sb_writers(struct super_block *s)
{
int i;

for (i = 0; i < SB_FREEZE_LEVELS; i++)
percpu_counter_destroy(&s->s_writers.counter[i]);
}

/**
* alloc_super - create new superblock
* @type: filesystem type superblock should belong to
Expand All @@ -117,18 +153,19 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)

if (s) {
if (security_sb_alloc(s)) {
/*
* We cannot call security_sb_free() without
* security_sb_alloc() succeeding. So bail out manually
*/
kfree(s);
s = NULL;
goto out;
}
#ifdef CONFIG_SMP
s->s_files = alloc_percpu(struct list_head);
if (!s->s_files) {
security_sb_free(s);
kfree(s);
s = NULL;
goto out;
} else {
if (!s->s_files)
goto err_out;
else {
int i;

for_each_possible_cpu(i)
Expand All @@ -137,6 +174,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)
#else
INIT_LIST_HEAD(&s->s_files);
#endif
if (init_sb_writers(s, type))
goto err_out;
s->s_flags = flags;
s->s_bdi = &default_backing_dev_info;
INIT_HLIST_NODE(&s->s_instances);
Expand Down Expand Up @@ -190,6 +229,16 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)
}
out:
return s;
err_out:
security_sb_free(s);
#ifdef CONFIG_SMP
if (s->s_files)
free_percpu(s->s_files);
#endif
destroy_sb_writers(s);
kfree(s);
s = NULL;
goto out;
}

/**
Expand All @@ -203,6 +252,7 @@ static inline void destroy_super(struct super_block *s)
#ifdef CONFIG_SMP
free_percpu(s->s_files);
#endif
destroy_sb_writers(s);
security_sb_free(s);
WARN_ON(!list_empty(&s->s_mounts));
kfree(s->s_subtype);
Expand Down Expand Up @@ -651,10 +701,11 @@ struct super_block *get_super_thawed(struct block_device *bdev)
{
while (1) {
struct super_block *s = get_super(bdev);
if (!s || s->s_frozen == SB_UNFROZEN)
if (!s || s->s_writers.frozen == SB_UNFROZEN)
return s;
up_read(&s->s_umount);
vfs_check_frozen(s, SB_FREEZE_WRITE);
wait_event(s->s_writers.wait_unfrozen,
s->s_writers.frozen == SB_UNFROZEN);
put_super(s);
}
}
Expand Down Expand Up @@ -732,7 +783,7 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
int retval;
int remount_ro;

if (sb->s_frozen != SB_UNFROZEN)
if (sb->s_writers.frozen != SB_UNFROZEN)
return -EBUSY;

#ifdef CONFIG_BLOCK
Expand Down Expand Up @@ -1163,21 +1214,160 @@ mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
return ERR_PTR(error);
}

/*
* This is an internal function, please use sb_end_{write,pagefault,intwrite}
* instead.
*/
void __sb_end_write(struct super_block *sb, int level)
{
percpu_counter_dec(&sb->s_writers.counter[level-1]);
/*
* Make sure s_writers are updated before we wake up waiters in
* freeze_super().
*/
smp_mb();
if (waitqueue_active(&sb->s_writers.wait))
wake_up(&sb->s_writers.wait);
rwsem_release(&sb->s_writers.lock_map[level-1], 1, _RET_IP_);
}
EXPORT_SYMBOL(__sb_end_write);

#ifdef CONFIG_LOCKDEP
/*
* We want lockdep to tell us about possible deadlocks with freezing but
* it's it bit tricky to properly instrument it. Getting a freeze protection
* works as getting a read lock but there are subtle problems. XFS for example
* gets freeze protection on internal level twice in some cases, which is OK
* only because we already hold a freeze protection also on higher level. Due
* to these cases we have to tell lockdep we are doing trylock when we
* already hold a freeze protection for a higher freeze level.
*/
static void acquire_freeze_lock(struct super_block *sb, int level, bool trylock,
unsigned long ip)
{
int i;

if (!trylock) {
for (i = 0; i < level - 1; i++)
if (lock_is_held(&sb->s_writers.lock_map[i])) {
trylock = true;
break;
}
}
rwsem_acquire_read(&sb->s_writers.lock_map[level-1], 0, trylock, ip);
}
#endif

/*
* This is an internal function, please use sb_start_{write,pagefault,intwrite}
* instead.
*/
int __sb_start_write(struct super_block *sb, int level, bool wait)
{
retry:
if (unlikely(sb->s_writers.frozen >= level)) {
if (!wait)
return 0;
wait_event(sb->s_writers.wait_unfrozen,
sb->s_writers.frozen < level);
}

#ifdef CONFIG_LOCKDEP
acquire_freeze_lock(sb, level, !wait, _RET_IP_);
#endif
percpu_counter_inc(&sb->s_writers.counter[level-1]);
/*
* Make sure counter is updated before we check for frozen.
* freeze_super() first sets frozen and then checks the counter.
*/
smp_mb();
if (unlikely(sb->s_writers.frozen >= level)) {
__sb_end_write(sb, level);
goto retry;
}
return 1;
}
EXPORT_SYMBOL(__sb_start_write);

/**
* sb_wait_write - wait until all writers to given file system finish
* @sb: the super for which we wait
* @level: type of writers we wait for (normal vs page fault)
*
* This function waits until there are no writers of given type to given file
* system. Caller of this function should make sure there can be no new writers
* of type @level before calling this function. Otherwise this function can
* livelock.
*/
static void sb_wait_write(struct super_block *sb, int level)
{
s64 writers;

/*
* We just cycle-through lockdep here so that it does not complain
* about returning with lock to userspace
*/
rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_);

do {
DEFINE_WAIT(wait);

/*
* We use a barrier in prepare_to_wait() to separate setting
* of frozen and checking of the counter
*/
prepare_to_wait(&sb->s_writers.wait, &wait,
TASK_UNINTERRUPTIBLE);

writers = percpu_counter_sum(&sb->s_writers.counter[level-1]);
if (writers)
schedule();

finish_wait(&sb->s_writers.wait, &wait);
} while (writers);
}

/**
* freeze_super - lock the filesystem and force it into a consistent state
* @sb: the super to lock
*
* Syncs the super to make sure the filesystem is consistent and calls the fs's
* freeze_fs. Subsequent calls to this without first thawing the fs will return
* -EBUSY.
*
* During this function, sb->s_writers.frozen goes through these values:
*
* SB_UNFROZEN: File system is normal, all writes progress as usual.
*
* SB_FREEZE_WRITE: The file system is in the process of being frozen. New
* writes should be blocked, though page faults are still allowed. We wait for
* all writes to complete and then proceed to the next stage.
*
* SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
* but internal fs threads can still modify the filesystem (although they
* should not dirty new pages or inodes), writeback can run etc. After waiting
* for all running page faults we sync the filesystem which will clean all
* dirty pages and inodes (no new dirty pages or inodes can be created when
* sync is running).
*
* SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
* modification are blocked (e.g. XFS preallocation truncation on inode
* reclaim). This is usually implemented by blocking new transactions for
* filesystems that have them and need this additional guard. After all
* internal writers are finished we call ->freeze_fs() to finish filesystem
* freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
* mostly auxiliary for filesystems to verify they do not modify frozen fs.
*
* sb->s_writers.frozen is protected by sb->s_umount.
*/
int freeze_super(struct super_block *sb)
{
int ret;

atomic_inc(&sb->s_active);
down_write(&sb->s_umount);
if (sb->s_frozen) {
if (sb->s_writers.frozen != SB_UNFROZEN) {
deactivate_locked_super(sb);
return -EBUSY;
}
Expand All @@ -1188,33 +1378,53 @@ int freeze_super(struct super_block *sb)
}

if (sb->s_flags & MS_RDONLY) {
sb->s_frozen = SB_FREEZE_TRANS;
smp_wmb();
/* Nothing to do really... */
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
up_write(&sb->s_umount);
return 0;
}

sb->s_frozen = SB_FREEZE_WRITE;
/* From now on, no new normal writers can start */
sb->s_writers.frozen = SB_FREEZE_WRITE;
smp_wmb();

/* Release s_umount to preserve sb_start_write -> s_umount ordering */
up_write(&sb->s_umount);

sb_wait_write(sb, SB_FREEZE_WRITE);

/* Now we go and block page faults... */
down_write(&sb->s_umount);
sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
smp_wmb();

sb_wait_write(sb, SB_FREEZE_PAGEFAULT);

/* All writers are done so after syncing there won't be dirty data */
sync_filesystem(sb);

sb->s_frozen = SB_FREEZE_TRANS;
/* Now wait for internal filesystem counter */
sb->s_writers.frozen = SB_FREEZE_FS;
smp_wmb();
sb_wait_write(sb, SB_FREEZE_FS);

sync_blockdev(sb->s_bdev);
if (sb->s_op->freeze_fs) {
ret = sb->s_op->freeze_fs(sb);
if (ret) {
printk(KERN_ERR
"VFS:Filesystem freeze failed\n");
sb->s_frozen = SB_UNFROZEN;
sb->s_writers.frozen = SB_UNFROZEN;
smp_wmb();
wake_up(&sb->s_wait_unfrozen);
wake_up(&sb->s_writers.wait_unfrozen);
deactivate_locked_super(sb);
return ret;
}
}
/*
* This is just for debugging purposes so that fs can warn if it
* sees write activity when frozen is set to SB_FREEZE_COMPLETE.
*/
sb->s_writers.frozen = SB_FREEZE_COMPLETE;
up_write(&sb->s_umount);
return 0;
}
Expand All @@ -1231,7 +1441,7 @@ int thaw_super(struct super_block *sb)
int error;

down_write(&sb->s_umount);
if (sb->s_frozen == SB_UNFROZEN) {
if (sb->s_writers.frozen == SB_UNFROZEN) {
up_write(&sb->s_umount);
return -EINVAL;
}
Expand All @@ -1244,16 +1454,15 @@ int thaw_super(struct super_block *sb)
if (error) {
printk(KERN_ERR
"VFS:Filesystem thaw failed\n");
sb->s_frozen = SB_FREEZE_TRANS;
up_write(&sb->s_umount);
return error;
}
}

out:
sb->s_frozen = SB_UNFROZEN;
sb->s_writers.frozen = SB_UNFROZEN;
smp_wmb();
wake_up(&sb->s_wait_unfrozen);
wake_up(&sb->s_writers.wait_unfrozen);
deactivate_locked_super(sb);

return 0;
Expand Down
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