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@xxxxxxxxxxxx>
> Cc: Eric Sandeen <sandeen@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx>
> ---
>
> 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@xxxxxxxxxx>
> */
> -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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