From: Eric Sandeen <sandeen@redhat.com>
To: "Fernando Luis Vázquez Cao" <fernando_b1@lab.ntt.co.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Josef Bacik <jbacik@fusionio.com>,
Dave Chinner <dchinner@redhat.com>,
Christoph Hellwig <hch@infradead.org>, Jan Kara <jack@suse.cz>,
linux-fsdevel@vger.kernel.org
Subject: Re: [RFC 2/9] fsfreeze: add unlocked version of thaw_super
Date: Thu, 13 Sep 2012 13:13:46 -0500 [thread overview]
Message-ID: <5052225A.7090107@redhat.com> (raw)
In-Reply-To: <1347534107.5646.6.camel@nexus.lab.ntt.co.jp>
On 9/13/12 6:01 AM, Fernando Luis Vázquez Cao wrote:
> thaw_super may be called with superblock lock already taken (fsfreeze's
> emergency thaw being one example), so we need an unlocked version to avoid
> lockups.
>
> Cc: Josef Bacik <jbacik@fusionio.com>
> Cc: Eric Sandeen <sandeen@redhat.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
> ---
>
> diff -urNp linux-3.6-rc5-orig/fs/super.c linux-3.6-rc5/fs/super.c
> --- linux-3.6-rc5-orig/fs/super.c 2012-09-12 19:13:00.710047001 +0900
> +++ linux-3.6-rc5/fs/super.c 2012-09-12 19:13:12.185924077 +0900
> @@ -1420,40 +1420,58 @@ int freeze_super(struct super_block *sb)
> EXPORT_SYMBOL(freeze_super);
>
> /**
> - * thaw_super -- unlock filesystem
> + * __thaw_super -- unlock filesystem
> * @sb: the super to thaw
> *
> - * Unlocks the filesystem and marks it writeable again after freeze_super().
> + * Unlocks the filesystem and marks it writeable again.
> + *
> + * This is the unlocked version of thaw_super, so it is the caller's job to
> + * to protect the superblock by grabing the s_umount semaphore in write mode.
s/grabing/grabbing/ - and maybe:
+ * and release it again on return, see thaw_super().
But the logic looks fine,
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
> */
> -int thaw_super(struct super_block *sb)
> +int __thaw_super(struct super_block *sb)
> {
> - int error;
> + int error = 0;
>
> - down_write(&sb->s_umount);
> if (sb->s_writers.frozen == SB_UNFROZEN) {
> - up_write(&sb->s_umount);
> - return -EINVAL;
> + error = -EINVAL;
> + goto out;
> }
>
> if (sb->s_flags & MS_RDONLY)
> - goto out;
> + goto out_thaw;
>
> if (sb->s_op->unfreeze_fs) {
> error = sb->s_op->unfreeze_fs(sb);
> if (error) {
> printk(KERN_ERR
> "VFS:Filesystem thaw failed\n");
> - up_write(&sb->s_umount);
> - return error;
> + goto out;
> }
> }
>
> -out:
> +out_thaw:
> sb->s_writers.frozen = SB_UNFROZEN;
> smp_wmb();
> wake_up(&sb->s_writers.wait_unfrozen);
> - deactivate_locked_super(sb);
> +out:
> + return error;
> +}
>
> - return 0;
> +/**
> + * thaw_super -- unlock filesystem
> + * @sb: the super to thaw
> + *
> + * Unlocks the filesystem and marks it writeable again after freeze_super().
> + */
> +int thaw_super(struct super_block *sb)
> +{
> + int res;
> + down_write(&sb->s_umount);
> + res = __thaw_super(sb);
> + if (!res)
> + deactivate_locked_super(sb);
> + else
> + up_write(&sb->s_umount);
> + return res;
> }
> EXPORT_SYMBOL(thaw_super);
> diff -urNp linux-3.6-rc5-orig/include/linux/fs.h linux-3.6-rc5/include/linux/fs.h
> --- linux-3.6-rc5-orig/include/linux/fs.h 2012-09-12 19:13:00.830047035 +0900
> +++ linux-3.6-rc5/include/linux/fs.h 2012-09-12 19:13:12.197929820 +0900
> @@ -2082,6 +2082,7 @@ extern int user_statfs(const char __user
> extern int fd_statfs(int, struct kstatfs *);
> extern int vfs_ustat(dev_t, struct kstatfs *);
> extern int freeze_super(struct super_block *super);
> +extern int __thaw_super(struct super_block *super);
> extern int thaw_super(struct super_block *super);
> extern bool our_mnt(struct vfsmount *mnt);
>
>
>
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next prev parent reply other threads:[~2012-09-13 18:13 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-13 10:57 [RFC 0/9 v3] fsfreeze: miscellaneous fixes and cleanups Fernando Luis Vázquez Cao
2012-09-13 11:00 ` [PATCH 1/9] vfs: add __iterate_supers() helper Fernando Luis Vázquez Cao
2012-09-14 2:36 ` Eric Sandeen
2012-09-14 2:40 ` Fernando Luis Vazquez Cao
2012-09-13 11:01 ` [RFC 2/9] fsfreeze: add unlocked version of thaw_super Fernando Luis Vázquez Cao
2012-09-13 18:13 ` Eric Sandeen [this message]
2012-09-13 11:03 ` [RFC 3/9] fsfreeze: Prevent emergency thaw from looping infinitely Fernando Luis Vázquez Cao
2012-09-13 16:40 ` Eric Sandeen
2012-09-13 11:04 ` [RFC 4/9] fsfreeze: emergency thaw will deadlock on s_umount Fernando Luis Vázquez Cao
2012-09-13 11:07 ` [RFC 5/9] xfs: switch to using super methods for fsfreeze Fernando Luis Vázquez Cao
2012-09-13 11:08 ` [RFC 6/9] fsfreeze: move emergency thaw code to fs/super.c Fernando Luis Vázquez Cao
2012-09-13 19:00 ` Josef Bacik
2012-09-13 21:10 ` Eric Sandeen
2012-09-14 2:11 ` Fernando Luis Vazquez Cao
2012-09-14 1:59 ` Fernando Luis Vazquez Cao
2012-09-13 11:10 ` [PATCH 7/9] fsfreeze: freeze_super and thaw_bdev don't play well together Fernando Luis Vázquez Cao
2012-09-13 11:11 ` [PATCH 8/9] fsfreeze: add vfs ioctl to check freeze state Fernando Luis Vázquez Cao
2012-09-13 11:13 ` [PATCH 9/9] fsfreeze: add block device " Fernando Luis Vázquez Cao
2012-09-14 0:57 ` [RFC 0/9 v3] fsfreeze: miscellaneous fixes and cleanups Dave Chinner
2012-09-14 2:20 ` Fernando Luis Vazquez Cao
2012-09-14 2:33 ` Eric Sandeen
2012-09-14 2:48 ` Fernando Luis Vazquez Cao
2012-09-14 6:22 ` Fernando Luis Vazquez Cao
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