Commit 7ba5d5d0 authored by yangerkun's avatar yangerkun Committed by Xie XiuQi
Browse files

fs/dcache.c: avoid softlock since too many negative dentry 



euler inclusion
category: bugfix
bugzilla: 15743
CVE: NA
---------------------------

Parallel thread to add negative dentry under root dir. Sometimes later,
'systemctl daemon-reload' will report softlockup since
__fsnotify_update_child_dentry_flags need update all child under root
dentry without distinguish does it active or not. It will waste so long
time with catching d_lock of root dentry. And other thread try to
spin_lock d_lock will run overtime.

Limit negative dentry under dir can avoid this.

Signed-off-by: default avataryangerkun <yangerkun@huawei.com>
Reviewed-by: default avatarMiao Xie <miaoxie@huawei.com>
Signed-off-by: default avatarYang Yingliang <yangyingliang@huawei.com>
parent 3cd16d87

fs/dcache.c

+42 −2
Original line number Diff line number Diff line
@@ -316,12 +316,20 @@ static inline void __d_set_inode_and_type(struct dentry *dentry, 
					  unsigned type_flags)

{

	unsigned flags;

	struct dentry *parent;



	parent = dentry->d_parent;

	if ((dentry->d_flags & DCACHE_NEGATIVE_ACCOUNT) && parent) {

		WARN_ON(!inode);

		atomic_dec(&parent->d_neg_dnum);

	}



	dentry->d_inode = inode;

	/* paired with smp_rmb() in lookup_fast() */

	smp_wmb();

	flags = READ_ONCE(dentry->d_flags);

	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);

	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU |

			DCACHE_NEGATIVE_ACCOUNT);

	flags |= type_flags;

	WRITE_ONCE(dentry->d_flags, flags);

}
@@ -338,6 +346,7 @@ static inline void __d_clear_type_and_inode(struct dentry *dentry) 
static void dentry_free(struct dentry *dentry)

{

	WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));

	WARN_ON(dentry->d_flags & DCACHE_NEGATIVE_ACCOUNT);

	if (unlikely(dname_external(dentry))) {

		struct external_name *p = external_name(dentry);

		if (likely(atomic_dec_and_test(&p->u.count))) {
@@ -562,8 +571,14 @@ static void __dentry_kill(struct dentry *dentry) 
	/* if it was on the hash then remove it */

	__d_drop(dentry);

	dentry_unlist(dentry, parent);

	if (parent)

	if (parent) {

		if (dentry->d_flags & DCACHE_NEGATIVE_ACCOUNT) {

			atomic_dec(&parent->d_neg_dnum);

			dentry->d_flags &= ~DCACHE_NEGATIVE_ACCOUNT;

		}



		spin_unlock(&parent->d_lock);

	}

	if (dentry->d_inode)

		dentry_unlink_inode(dentry);

	else
@@ -623,6 +638,8 @@ static inline struct dentry *lock_parent(struct dentry *dentry) 


static inline bool retain_dentry(struct dentry *dentry)

{

	struct dentry *parent;



	WARN_ON(d_in_lookup(dentry));



	/* Unreachable? Get rid of it */
@@ -636,6 +653,28 @@ static inline bool retain_dentry(struct dentry *dentry) 
		if (dentry->d_op->d_delete(dentry))

			return false;

	}



	if (unlikely(!dentry->d_parent))

		goto noparent;



	parent = dentry->d_parent;

	/* Return false if it's negative */

	WARN_ON((atomic_read(&parent->d_neg_dnum) < 0));

	if (!dentry->d_inode) {

		if (!(dentry->d_flags & DCACHE_NEGATIVE_ACCOUNT)) {

			unsigned flags = READ_ONCE(dentry->d_flags);



			flags |= DCACHE_NEGATIVE_ACCOUNT;

			WRITE_ONCE(dentry->d_flags, flags);

			atomic_inc(&parent->d_neg_dnum);

		}

	}



	if (!dentry->d_inode &&

	    atomic_read(&parent->d_neg_dnum) >= NEG_DENTRY_LIMIT)

		return false;



noparent:

	/* retain; LRU fodder */

	dentry->d_lockref.count--;

	if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
@@ -1651,6 +1690,7 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name) 
	seqcount_init(&dentry->d_seq);

	dentry->d_inode = NULL;

	dentry->d_parent = dentry;

	atomic_set(&dentry->d_neg_dnum, 0);

	dentry->d_sb = sb;

	dentry->d_op = NULL;

	dentry->d_fsdata = NULL;

include/linux/dcache.h

+4 −0
Original line number Diff line number Diff line
@@ -84,6 +84,7 @@ extern struct dentry_stat_t dentry_stat; 
# endif

#endif



#define NEG_DENTRY_LIMIT 16384

#define d_lock	d_lockref.lock



struct dentry {
@@ -119,6 +120,8 @@ struct dentry { 
	 	struct rcu_head d_rcu;

	} d_u;



	/* negative dentry under this dentry, if it's dir */

	atomic_t d_neg_dnum;

	KABI_RESERVE(1)

	KABI_RESERVE(2)

} __randomize_layout;
@@ -225,6 +228,7 @@ struct dentry_operations { 


#define DCACHE_PAR_LOOKUP		0x10000000 /* being looked up (with parent locked shared) */

#define DCACHE_DENTRY_CURSOR		0x20000000

#define DCACHE_NEGATIVE_ACCOUNT		0x40000000



extern seqlock_t rename_lock;