3.16.61-rc1 review patch. If anyone has any objections, please let me know.
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From: Al Viro viro@zeniv.linux.org.uk
commit a528aca7f359f4b0b1d72ae406097e491a5ba9ea upstream.
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.
Signed-off-by: Al Viro viro@zeniv.linux.org.uk [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- fs/dcache.c | 20 +++++--------------- include/linux/dcache.h | 4 +--- 2 files changed, 6 insertions(+), 18 deletions(-)
--- a/fs/dcache.c +++ b/fs/dcache.c @@ -291,28 +291,18 @@ static inline void __d_set_inode_and_typ unsigned flags;
dentry->d_inode = inode; - smp_wmb(); flags = ACCESS_ONCE(dentry->d_flags); flags &= ~DCACHE_ENTRY_TYPE; flags |= type_flags; ACCESS_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 = ACCESS_ONCE(dentry->d_flags);
flags &= ~DCACHE_ENTRY_TYPE; ACCESS_ONCE(dentry->d_flags) = flags; - smp_wmb(); dentry->d_inode = NULL; }
@@ -376,9 +366,11 @@ static void dentry_unlink_inode(struct d __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_barrier(dentry); + raw_write_seqcount_end(&dentry->d_seq); spin_unlock(&dentry->d_lock); spin_unlock(&inode->i_lock); if (!inode->i_nlink) @@ -1680,8 +1672,9 @@ static void __d_instantiate(struct dentr 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_barrier(dentry); + raw_write_seqcount_end(&dentry->d_seq); spin_unlock(&dentry->d_lock); fsnotify_d_instantiate(dentry, inode); } --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -413,9 +413,7 @@ static inline bool d_mountpoint(const st */ static inline unsigned __d_entry_type(const struct dentry *dentry) { - unsigned type = ACCESS_ONCE(dentry->d_flags); - smp_rmb(); - return type & DCACHE_ENTRY_TYPE; + return dentry->d_flags & DCACHE_ENTRY_TYPE; }
static inline bool d_can_lookup(const struct dentry *dentry)