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Commit a528aca7 authored by Al Viro's avatar Al Viro
Browse files

use ->d_seq to get coherency between ->d_inode and ->d_flags 



Games with ordering and barriers are way too brittle.  Just
bump ->d_seq before and after updating ->d_inode and ->d_flags
type bits, so that verifying ->d_seq would guarantee they are
coherent.

Cc: stable@vger.kernel.org # v3.13+
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 5129fa48

fs/dcache.c

+5 −15
Original line number Diff line number Diff line
@@ -269,9 +269,6 @@ static inline int dname_external(const struct dentry *dentry) 
	return dentry->d_name.name != dentry->d_iname;

}



/*

 * Make sure other CPUs see the inode attached before the type is set.

 */

static inline void __d_set_inode_and_type(struct dentry *dentry,

					  struct inode *inode,

					  unsigned type_flags)
@@ -279,28 +276,18 @@ static inline void __d_set_inode_and_type(struct dentry *dentry, 
	unsigned flags;



	dentry->d_inode = inode;

	smp_wmb();

	flags = READ_ONCE(dentry->d_flags);

	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);

	flags |= type_flags;

	WRITE_ONCE(dentry->d_flags, flags);

}



/*

 * Ideally, we want to make sure that other CPUs see the flags cleared before

 * the inode is detached, but this is really a violation of RCU principles

 * since the ordering suggests we should always set inode before flags.

 *

 * We should instead replace or discard the entire dentry - but that sucks

 * performancewise on mass deletion/rename.

 */

static inline void __d_clear_type_and_inode(struct dentry *dentry)

{

	unsigned flags = READ_ONCE(dentry->d_flags);



	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);

	WRITE_ONCE(dentry->d_flags, flags);

	smp_wmb();

	dentry->d_inode = NULL;

}
@@ -370,9 +357,11 @@ static void dentry_unlink_inode(struct dentry * dentry) 
	__releases(dentry->d_inode->i_lock)

{

	struct inode *inode = dentry->d_inode;



	raw_write_seqcount_begin(&dentry->d_seq);

	__d_clear_type_and_inode(dentry);

	hlist_del_init(&dentry->d_u.d_alias);

	dentry_rcuwalk_invalidate(dentry);

	raw_write_seqcount_end(&dentry->d_seq);

	spin_unlock(&dentry->d_lock);

	spin_unlock(&inode->i_lock);

	if (!inode->i_nlink)
@@ -1758,8 +1747,9 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode) 
	spin_lock(&dentry->d_lock);

	if (inode)

		hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);

	raw_write_seqcount_begin(&dentry->d_seq);

	__d_set_inode_and_type(dentry, inode, add_flags);

	dentry_rcuwalk_invalidate(dentry);

	raw_write_seqcount_end(&dentry->d_seq);

	spin_unlock(&dentry->d_lock);

	fsnotify_d_instantiate(dentry, inode);

}

include/linux/dcache.h

+1 −3
Original line number Diff line number Diff line
@@ -409,9 +409,7 @@ static inline bool d_mountpoint(const struct dentry *dentry) 
 */

static inline unsigned __d_entry_type(const struct dentry *dentry)

{

	unsigned type = READ_ONCE(dentry->d_flags);

	smp_rmb();

	return type & DCACHE_ENTRY_TYPE;

	return dentry->d_flags & DCACHE_ENTRY_TYPE;

}



static inline bool d_is_miss(const struct dentry *dentry)