Commit a528aca7 authored by Al Viro's avatar Al Viro

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
...@@ -269,9 +269,6 @@ static inline int dname_external(const struct dentry *dentry) ...@@ -269,9 +269,6 @@ static inline int dname_external(const struct dentry *dentry)
return dentry->d_name.name != dentry->d_iname; 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, static inline void __d_set_inode_and_type(struct dentry *dentry,
struct inode *inode, struct inode *inode,
unsigned type_flags) unsigned type_flags)
...@@ -279,28 +276,18 @@ static inline void __d_set_inode_and_type(struct dentry *dentry, ...@@ -279,28 +276,18 @@ static inline void __d_set_inode_and_type(struct dentry *dentry,
unsigned flags; unsigned flags;
dentry->d_inode = inode; dentry->d_inode = inode;
smp_wmb();
flags = READ_ONCE(dentry->d_flags); flags = READ_ONCE(dentry->d_flags);
flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU); flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
flags |= type_flags; flags |= type_flags;
WRITE_ONCE(dentry->d_flags, 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) static inline void __d_clear_type_and_inode(struct dentry *dentry)
{ {
unsigned flags = READ_ONCE(dentry->d_flags); unsigned flags = READ_ONCE(dentry->d_flags);
flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU); flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
WRITE_ONCE(dentry->d_flags, flags); WRITE_ONCE(dentry->d_flags, flags);
smp_wmb();
dentry->d_inode = NULL; dentry->d_inode = NULL;
} }
...@@ -370,9 +357,11 @@ static void dentry_unlink_inode(struct dentry * dentry) ...@@ -370,9 +357,11 @@ static void dentry_unlink_inode(struct dentry * dentry)
__releases(dentry->d_inode->i_lock) __releases(dentry->d_inode->i_lock)
{ {
struct inode *inode = dentry->d_inode; struct inode *inode = dentry->d_inode;
raw_write_seqcount_begin(&dentry->d_seq);
__d_clear_type_and_inode(dentry); __d_clear_type_and_inode(dentry);
hlist_del_init(&dentry->d_u.d_alias); 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(&dentry->d_lock);
spin_unlock(&inode->i_lock); spin_unlock(&inode->i_lock);
if (!inode->i_nlink) if (!inode->i_nlink)
...@@ -1758,8 +1747,9 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode) ...@@ -1758,8 +1747,9 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode)
spin_lock(&dentry->d_lock); spin_lock(&dentry->d_lock);
if (inode) if (inode)
hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry); 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); __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); spin_unlock(&dentry->d_lock);
fsnotify_d_instantiate(dentry, inode); fsnotify_d_instantiate(dentry, inode);
} }
......
...@@ -409,9 +409,7 @@ static inline bool d_mountpoint(const struct dentry *dentry) ...@@ -409,9 +409,7 @@ static inline bool d_mountpoint(const struct dentry *dentry)
*/ */
static inline unsigned __d_entry_type(const struct dentry *dentry) static inline unsigned __d_entry_type(const struct dentry *dentry)
{ {
unsigned type = READ_ONCE(dentry->d_flags); return dentry->d_flags & DCACHE_ENTRY_TYPE;
smp_rmb();
return type & DCACHE_ENTRY_TYPE;
} }
static inline bool d_is_miss(const struct dentry *dentry) static inline bool d_is_miss(const struct dentry *dentry)
......
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