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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: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2016-02-29 12:12:46 -05:00
parent 5129fa482b
commit a528aca7f3
2 changed files with 6 additions and 18 deletions
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20
fs/dcache.c
View File

@ -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);
}

4
include/linux/dcache.h
View File

@ -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)