From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:44700 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726422AbeLRNqz (ORCPT ); Tue, 18 Dec 2018 08:46:55 -0500 From: Jan Kara To: Al Viro Cc: , Jan Kara Subject: [PATCH 1/2] vfs: Provide function to grab superblock reference Date: Tue, 18 Dec 2018 14:46:41 +0100 Message-Id: <20181218134642.21219-2-jack@suse.cz> In-Reply-To: <20181218134642.21219-1-jack@suse.cz> References: <20181218134642.21219-1-jack@suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Provide function to hold superblock reference when we are sure the superblock is active. This function will get used by code reading /proc/mounts and friends. Signed-off-by: Jan Kara --- fs/internal.h | 2 ++ fs/super.c | 35 +++++++++++++++++++++++++++++++++++ 2 files changed, 37 insertions(+) diff --git a/fs/internal.h b/fs/internal.h index d410186bc369..c2c92be1e7df 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -104,6 +104,8 @@ extern bool trylock_super(struct super_block *sb); extern struct dentry *mount_fs(struct file_system_type *, int, const char *, void *); extern struct super_block *user_get_super(dev_t); +extern void hold_sb(struct super_block *sb); +extern bool mount_trylock_super(struct super_block *sb); /* * open.c diff --git a/fs/super.c b/fs/super.c index ca53a08497ed..552d6247053b 100644 --- a/fs/super.c +++ b/fs/super.c @@ -775,6 +775,41 @@ struct super_block *get_super_exclusive_thawed(struct block_device *bdev) } EXPORT_SYMBOL(get_super_exclusive_thawed); +/** + * hold_sb - get superblock reference for active superblock + * @sb: superblock to get reference for + * + * Get reference to superblock. The caller must make sure the superblock + * is currently active by other means (e.g. holding an active reference + * itself or holding namespace_sem preventing unmount). + */ +void hold_sb(struct super_block *sb) +{ + spin_lock(&sb_lock); + WARN_ON_ONCE(!atomic_read(&sb->s_active)); + sb->s_count++; + spin_unlock(&sb_lock); +} + +/** + * mount_trylock_super - get superblock and lock it against remount + * @sb: superblock to get reference for + * + * Get reference to superblock and protect superblock against racing + * remount or umount. The caller must make sure the superblock + * is currently active by other means (e.g. holding an active reference + * itself or holding namespace_sem preventing unmount). + */ +bool mount_trylock_super(struct super_block *sb) +{ + hold_sb(sb); + if (!down_read_trylock(&sb->s_umount)) { + put_super(sb); + return false; + } + return true; +} + /** * get_active_super - get an active reference to the superblock of a device * @bdev: device to get the superblock for -- 2.16.4