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SubjectRe: [PATCH 1/2] vfs: Provide function to get superblock and wait for it to thaw
On Thu 09-02-12 00:27:05, Jan Kara wrote:
> On Thu 09-02-12 10:20:49, Dave Chinner wrote:
> > On Tue, Feb 07, 2012 at 11:37:46PM +0100, Jan Kara wrote:
> > > In quota code we need to find a superblock corresponding to a device and wait
> > > for superblock to be unfrozen. However this waiting has to happen without
> > > s_umount semaphore because that is required for superblock to thaw. So provide
> > > a function in VFS for this to keep dances with s_umount where they belong.
> > >
> > > Signed-off-by: Jan Kara <jack@suse.cz>
> > > ---
> > > fs/super.c | 47 +++++++++++++++++++++++++++++++++++------------
> > > include/linux/fs.h | 1 +
> > > 2 files changed, 36 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/fs/super.c b/fs/super.c
> > > index 6015c02..e320239 100644
> > > --- a/fs/super.c
> > > +++ b/fs/super.c
> > > @@ -593,15 +593,7 @@ void iterate_supers_type(struct file_system_type *type,
> > >
> > > EXPORT_SYMBOL(iterate_supers_type);
> > >
> > > -/**
> > > - * get_super - get the superblock of a device
> > > - * @bdev: device to get the superblock for
> > > - *
> > > - * Scans the superblock list and finds the superblock of the file system
> > > - * mounted on the device given. %NULL is returned if no match is found.
> > > - */
> > > -
> > > -struct super_block *get_super(struct block_device *bdev)
> > > +static struct super_block *__get_super(struct block_device *bdev, bool thawed)
> > > {
> > > struct super_block *sb;
> > >
> > > @@ -618,9 +610,13 @@ rescan:
> > > spin_unlock(&sb_lock);
> > > down_read(&sb->s_umount);
> > > /* still alive? */
> > > - if (sb->s_root && (sb->s_flags & MS_BORN))
> > > - return sb;
> > > - up_read(&sb->s_umount);
> > > + if (sb->s_root && (sb->s_flags & MS_BORN)) {
> > > + if (sb->s_frozen == SB_UNFROZEN)
> > > + return sb;
> > > + up_read(&sb->s_umount);
> > > + vfs_check_frozen(sb, SB_FREEZE_WRITE);
> > > + } else
> > > + up_read(&sb->s_umount);
> > > /* nope, got unmounted */
> > > spin_lock(&sb_lock);
> > > __put_super(sb);
> > > @@ -631,9 +627,36 @@ rescan:
> > > return NULL;
> > > }
> >
> > The thawed parameter appears to be unused and the waiting for frozen
> > filesystems appears to happen for all callers. Is this intentional?
> Ah, sorry. Obviously that's a bug. Thanks for spotting it. I'll fix it
> up.
Attached is a fixed version.

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
From 5dce7adb0c281612a14fa3dd8c8d5ef3f5eb3666 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Tue, 7 Feb 2012 22:59:06 +0100
Subject: [PATCH 1/2] vfs: Provide function to get superblock and wait for it to thaw

In quota code we need to find a superblock corresponding to a device and wait
for superblock to be unfrozen. However this waiting has to happen without
s_umount semaphore because that is required for superblock to thaw. So provide
a function in VFS for this to keep dances with s_umount where they belong.

Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/super.c | 47 +++++++++++++++++++++++++++++++++++------------
include/linux/fs.h | 1 +
2 files changed, 36 insertions(+), 12 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index 6015c02..e15aaa9 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -593,15 +593,7 @@ void iterate_supers_type(struct file_system_type *type,

EXPORT_SYMBOL(iterate_supers_type);

-/**
- * get_super - get the superblock of a device
- * @bdev: device to get the superblock for
- *
- * Scans the superblock list and finds the superblock of the file system
- * mounted on the device given. %NULL is returned if no match is found.
- */
-
-struct super_block *get_super(struct block_device *bdev)
+static struct super_block *__get_super(struct block_device *bdev, bool thawed)
{
struct super_block *sb;

@@ -618,9 +610,13 @@ rescan:
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
/* still alive? */
- if (sb->s_root && (sb->s_flags & MS_BORN))
- return sb;
- up_read(&sb->s_umount);
+ if (sb->s_root && (sb->s_flags & MS_BORN)) {
+ if (!thawed || sb->s_frozen == SB_UNFROZEN)
+ return sb;
+ up_read(&sb->s_umount);
+ vfs_check_frozen(sb, SB_FREEZE_WRITE);
+ } else
+ up_read(&sb->s_umount);
/* nope, got unmounted */
spin_lock(&sb_lock);
__put_super(sb);
@@ -631,9 +627,36 @@ rescan:
return NULL;
}

+/**
+ * get_super - get the superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device given. %NULL is returned if no match is found.
+ */
+
+struct super_block *get_super(struct block_device *bdev)
+{
+ return __get_super(bdev, false);
+}
EXPORT_SYMBOL(get_super);

/**
+ * get_super_thawed - get thawed superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device given once the superblock is thawed. %NULL is
+ * returned if no match is found.
+ */
+
+struct super_block *get_super_thawed(struct block_device *bdev)
+{
+ return __get_super(bdev, true);
+}
+EXPORT_SYMBOL(get_super_thawed);
+
+/**
* get_active_super - get an active reference to the superblock of a device
* @bdev: device to get the superblock for
*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 386da09..69cd5bb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2496,6 +2496,7 @@ extern void get_filesystem(struct file_system_type *fs);
extern void put_filesystem(struct file_system_type *fs);
extern struct file_system_type *get_fs_type(const char *name);
extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_super_thawed(struct block_device *);
extern struct super_block *get_active_super(struct block_device *bdev);
extern void drop_super(struct super_block *sb);
extern void iterate_supers(void (*)(struct super_block *, void *), void *);
--
1.7.1
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