From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757805Ab2BHXrL (ORCPT ); Wed, 8 Feb 2012 18:47:11 -0500 Received: from cantor2.suse.de ([195.135.220.15]:37553 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754853Ab2BHXrG (ORCPT ); Wed, 8 Feb 2012 18:47:06 -0500 Date: Thu, 9 Feb 2012 00:47:03 +0100 From: Jan Kara To: Dave Chinner Cc: Jan Kara , Al Viro , linux-fsdevel@vger.kernel.org, LKML , mpatocka@redhat.com, sandeen@sandeen.net Subject: Re: [PATCH 1/2] vfs: Provide function to get superblock and wait for it to thaw Message-ID: <20120208234703.GG1696@quack.suse.cz> References: <1328654267-18855-1-git-send-email-jack@suse.cz> <1328654267-18855-2-git-send-email-jack@suse.cz> <20120208232049.GC7479@dastard> <20120208232705.GF1696@quack.suse.cz> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="vGgW1X5XWziG23Ko" Content-Disposition: inline In-Reply-To: <20120208232705.GF1696@quack.suse.cz> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --vGgW1X5XWziG23Ko Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 > > > --- > > > 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 SUSE Labs, CR --vGgW1X5XWziG23Ko Content-Type: text/x-patch; charset=us-ascii Content-Disposition: attachment; filename="0001-vfs-Provide-function-to-get-superblock-and-wait-for-.patch" >>From 5dce7adb0c281612a14fa3dd8c8d5ef3f5eb3666 Mon Sep 17 00:00:00 2001 From: Jan Kara 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 --- 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 --vGgW1X5XWziG23Ko--