From 7d6cd73d33b62021111a469b6a454ec357be295f Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 23 Nov 2016 13:16:10 +0100 Subject: [PATCH] quota: Hold s_umount in exclusive mode when enabling / disabling quotas Currently we hold s_umount semaphore only in shared mode when enabling or disabling quotas and use dqonoff_mutex for serializing quota state changes on a filesystem and also quota state changes with other places depending on current quota state. Using dedicated mutex for this causes possible deadlocks during filesystem freezing (see following commit for details) so we transition to using s_umount semaphore for the necessary synchronization whose lock ordering is properly handled by the filesystem freezing code. As a start grab s_umount in exclusive mode when enabling / disabling quotas. Signed-off-by: Jan Kara --- fs/quota/dquot.c | 11 +++++++++++ fs/quota/quota.c | 16 +++++++++++++--- 2 files changed, 24 insertions(+), 3 deletions(-) diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c index 1bfac28b7e7d..047afb966420 100644 --- a/fs/quota/dquot.c +++ b/fs/quota/dquot.c @@ -2107,6 +2107,10 @@ int dquot_disable(struct super_block *sb, int type, unsigned int flags) struct quota_info *dqopt = sb_dqopt(sb); struct inode *toputinode[MAXQUOTAS]; + /* s_umount should be held in exclusive mode */ + if (WARN_ON_ONCE(down_read_trylock(&sb->s_umount))) + up_read(&sb->s_umount); + /* Cannot turn off usage accounting without turning off limits, or * suspend quotas and simultaneously turn quotas off. */ if ((flags & DQUOT_USAGE_ENABLED && !(flags & DQUOT_LIMITS_ENABLED)) @@ -2371,6 +2375,10 @@ int dquot_resume(struct super_block *sb, int type) int ret = 0, cnt; unsigned int flags; + /* s_umount should be held in exclusive mode */ + if (WARN_ON_ONCE(down_read_trylock(&sb->s_umount))) + up_read(&sb->s_umount); + for (cnt = 0; cnt < MAXQUOTAS; cnt++) { if (type != -1 && cnt != type) continue; @@ -2430,6 +2438,9 @@ int dquot_enable(struct inode *inode, int type, int format_id, /* Just unsuspend quotas? */ BUG_ON(flags & DQUOT_SUSPENDED); + /* s_umount should be held in exclusive mode */ + if (WARN_ON_ONCE(down_read_trylock(&sb->s_umount))) + up_read(&sb->s_umount); if (!flags) return 0; diff --git a/fs/quota/quota.c b/fs/quota/quota.c index 2d445425aad7..6ce6f4b6826b 100644 --- a/fs/quota/quota.c +++ b/fs/quota/quota.c @@ -789,9 +789,14 @@ static int quotactl_cmd_write(int cmd) } return 1; } - #endif /* CONFIG_BLOCK */ +/* Return true if quotactl command is manipulating quota on/off state */ +static bool quotactl_cmd_onoff(int cmd) +{ + return (cmd == Q_QUOTAON) || (cmd == Q_QUOTAOFF); +} + /* * look up a superblock on which quota ops will be performed * - use the name of a block device to find the superblock thereon @@ -809,7 +814,9 @@ static struct super_block *quotactl_block(const char __user *special, int cmd) putname(tmp); if (IS_ERR(bdev)) return ERR_CAST(bdev); - if (quotactl_cmd_write(cmd)) + if (quotactl_cmd_onoff(cmd)) + sb = get_super_exclusive_thawed(bdev); + else if (quotactl_cmd_write(cmd)) sb = get_super_thawed(bdev); else sb = get_super(bdev); @@ -872,7 +879,10 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special, ret = do_quotactl(sb, type, cmds, id, addr, pathp); - drop_super(sb); + if (!quotactl_cmd_onoff(cmds)) + drop_super(sb); + else + drop_super_exclusive(sb); out: if (pathp && !IS_ERR(pathp)) path_put(pathp); -- 2.30.2