parallel lookups: actual switch to rwsem

ta-da!

The main issue is the lack of down_write_killable(), so the places
like readdir.c switched to plain inode_lock(); once killable
variants of rwsem primitives appear, that'll be dealt with.

lockdep side also might need more work

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index 8810e23..1567a53 100644 (file)
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -539,3 +539,21 @@ in your dentry operations instead.
        it's a symlink.  Checking ->i_mode is really needed now.  In-tree we had
        to fix shmem_destroy_callback() that used to take that kind of shortcut;
        watch out, since that shortcut is no longer valid.
+--
+[mandatory]
+       ->i_mutex is replaced with ->i_rwsem now.  inode_lock() et.al. work as
+       they used to - they just take it exclusive.  However, ->lookup() may be
+       called with parent locked shared.  Its instances must not
+               * use d_instantiate) and d_rehash() separately - use d_add() or
+                 d_splice_alias() instead.
+               * use d_rehash() alone - call d_add(new_dentry, NULL) instead.
+               * in the unlikely case when (read-only) access to filesystem
+                 data structures needs exclusion for some reason, arrange it
+                 yourself.  None of the in-tree filesystems needed that.
+               * rely on ->d_parent and ->d_name not changing after dentry has
+                 been fed to d_add() or d_splice_alias().  Again, none of the
+                 in-tree instances relied upon that.
+       We are guaranteed that lookups of the same name in the same directory
+       will not happen in parallel ("same" in the sense of your ->d_compare()).
+       Lookups on different names in the same directory can and do happen in
+       parallel now.

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 5a23806..0b8ba71 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -837,9 +837,11 @@ static noinline int btrfs_mksubvol(struct path *parent,
        struct dentry *dentry;
        int error;
 
-       error = mutex_lock_killable_nested(&dir->i_mutex, I_MUTEX_PARENT);
-       if (error == -EINTR)
-               return error;
+       inode_lock_nested(dir, I_MUTEX_PARENT);
+       // XXX: should've been
+       // mutex_lock_killable_nested(&dir->i_mutex, I_MUTEX_PARENT);
+       // if (error == -EINTR)
+       //      return error;
 
        dentry = lookup_one_len(name, parent->dentry, namelen);
        error = PTR_ERR(dentry);
@@ -2366,9 +2368,11 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
                goto out;
 
 
-       err = mutex_lock_killable_nested(&dir->i_mutex, I_MUTEX_PARENT);
-       if (err == -EINTR)
-               goto out_drop_write;
+       inode_lock_nested(dir, I_MUTEX_PARENT);
+       // XXX: should've been
+       // err = mutex_lock_killable_nested(&dir->i_mutex, I_MUTEX_PARENT);
+       // if (err == -EINTR)
+       //      goto out_drop_write;
        dentry = lookup_one_len(vol_args->name, parent, namelen);
        if (IS_ERR(dentry)) {
                err = PTR_ERR(dentry);
@@ -2558,7 +2562,7 @@ out_dput:
        dput(dentry);
 out_unlock_dir:
        inode_unlock(dir);
-out_drop_write:
+//out_drop_write:
        mnt_drop_write_file(file);
 out:
        kfree(vol_args);

diff --git a/fs/configfs/inode.c b/fs/configfs/inode.c
index 03d124a..0387968 100644 (file)
--- a/fs/configfs/inode.c
+++ b/fs/configfs/inode.c
@@ -156,7 +156,7 @@ static void configfs_set_inode_lock_class(struct configfs_dirent *sd,
 
        if (depth > 0) {
                if (depth <= ARRAY_SIZE(default_group_class)) {
-                       lockdep_set_class(&inode->i_mutex,
+                       lockdep_set_class(&inode->i_rwsem,
                                          &default_group_class[depth - 1]);
                } else {
                        /*

diff --git a/fs/dcache.c b/fs/dcache.c
index 59fcffc..e49ba7d 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2932,7 +2932,8 @@ struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
 static int __d_unalias(struct inode *inode,
                struct dentry *dentry, struct dentry *alias)
 {
-       struct mutex *m1 = NULL, *m2 = NULL;
+       struct mutex *m1 = NULL;
+       struct rw_semaphore *m2 = NULL;
        int ret = -ESTALE;
 
        /* If alias and dentry share a parent, then no extra locks required */
@@ -2943,15 +2944,15 @@ static int __d_unalias(struct inode *inode,
        if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
                goto out_err;
        m1 = &dentry->d_sb->s_vfs_rename_mutex;
-       if (!inode_trylock(alias->d_parent->d_inode))
+       if (!inode_trylock_shared(alias->d_parent->d_inode))
                goto out_err;
-       m2 = &alias->d_parent->d_inode->i_mutex;
+       m2 = &alias->d_parent->d_inode->i_rwsem;
 out_unalias:
        __d_move(alias, dentry, false);
        ret = 0;
 out_err:
        if (m2)
-               mutex_unlock(m2);
+               up_read(m2);
        if (m1)
                mutex_unlock(m1);
        return ret;

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index c09c63d..4546360 100644 (file)
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -824,7 +824,7 @@ static int init_inodes(struct gfs2_sbd *sdp, int undo)
         * i_mutex on quota files is special. Since this inode is hidden system
         * file, we are safe to define locking ourselves.
         */
-       lockdep_set_class(&sdp->sd_quota_inode->i_mutex,
+       lockdep_set_class(&sdp->sd_quota_inode->i_rwsem,
                          &gfs2_quota_imutex_key);
 
        error = gfs2_rindex_update(sdp);

diff --git a/fs/inode.c b/fs/inode.c
index 4b884f7..4ccbc21 100644 (file)
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -166,8 +166,8 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
        spin_lock_init(&inode->i_lock);
        lockdep_set_class(&inode->i_lock, &sb->s_type->i_lock_key);
 
-       mutex_init(&inode->i_mutex);
-       lockdep_set_class(&inode->i_mutex, &sb->s_type->i_mutex_key);
+       init_rwsem(&inode->i_rwsem);
+       lockdep_set_class(&inode->i_rwsem, &sb->s_type->i_mutex_key);
 
        atomic_set(&inode->i_dio_count, 0);
 
@@ -925,13 +925,13 @@ void lockdep_annotate_inode_mutex_key(struct inode *inode)
                struct file_system_type *type = inode->i_sb->s_type;
 
                /* Set new key only if filesystem hasn't already changed it */
-               if (lockdep_match_class(&inode->i_mutex, &type->i_mutex_key)) {
+               if (lockdep_match_class(&inode->i_rwsem, &type->i_mutex_key)) {
                        /*
                         * ensure nobody is actually holding i_mutex
                         */
-                       mutex_destroy(&inode->i_mutex);
-                       mutex_init(&inode->i_mutex);
-                       lockdep_set_class(&inode->i_mutex,
+                       // mutex_destroy(&inode->i_mutex);
+                       init_rwsem(&inode->i_rwsem);
+                       lockdep_set_class(&inode->i_rwsem,
                                          &type->i_mutex_dir_key);
                }
        }

diff --git a/fs/namei.c b/fs/namei.c
index 7babb5e..8249852 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1607,7 +1607,7 @@ static struct dentry *lookup_slow(const struct qstr *name,
        struct inode *inode = dir->d_inode;
        DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
 
-       inode_lock(inode);
+       inode_lock_shared(inode);
        /* Don't go there if it's already dead */
        if (unlikely(IS_DEADDIR(inode)))
                goto out;
@@ -1638,7 +1638,7 @@ again:
                }
        }
 out:
-       inode_unlock(inode);
+       inode_unlock_shared(inode);
        return dentry;
 }
 

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 12f4a9e..0748777 100644 (file)
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -262,7 +262,7 @@ static int ocfs2_init_locked_inode(struct inode *inode, void *opaque)
        inode->i_ino = args->fi_ino;
        OCFS2_I(inode)->ip_blkno = args->fi_blkno;
        if (args->fi_sysfile_type != 0)
-               lockdep_set_class(&inode->i_mutex,
+               lockdep_set_class(&inode->i_rwsem,
                        &ocfs2_sysfile_lock_key[args->fi_sysfile_type]);
        if (args->fi_sysfile_type == USER_QUOTA_SYSTEM_INODE ||
            args->fi_sysfile_type == GROUP_QUOTA_SYSTEM_INODE ||

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 6ec1e43..da186ee 100644 (file)
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -218,7 +218,9 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
        cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
        old_cred = override_creds(override_cred);
 
-       err = mutex_lock_killable(&dir->d_inode->i_mutex);
+       inode_lock(dir->d_inode);
+       err = 0;
+       // XXX: err = mutex_lock_killable(&dir->d_inode->i_mutex);
        if (!err) {
                while (rdd->first_maybe_whiteout) {
                        p = rdd->first_maybe_whiteout;

diff --git a/fs/readdir.c b/fs/readdir.c
index e69ef3b..bf583e8 100644 (file)
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -32,9 +32,10 @@ int iterate_dir(struct file *file, struct dir_context *ctx)
        if (res)
                goto out;
 
-       res = mutex_lock_killable(&inode->i_mutex);
-       if (res)
-               goto out;
+       inode_lock(inode);
+       // res = mutex_lock_killable(&inode->i_mutex);
+       // if (res)
+       //      goto out;
 
        res = -ENOENT;
        if (!IS_DEADDIR(inode)) {

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 00cecc5..3018f31 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -647,7 +647,7 @@ struct inode {
 
        /* Misc */
        unsigned long           i_state;
-       struct mutex            i_mutex;
+       struct rw_semaphore     i_rwsem;
 
        unsigned long           dirtied_when;   /* jiffies of first dirtying */
        unsigned long           dirtied_time_when;
@@ -734,27 +734,42 @@ enum inode_i_mutex_lock_class
 
 static inline void inode_lock(struct inode *inode)
 {
-       mutex_lock(&inode->i_mutex);
+       down_write(&inode->i_rwsem);
 }
 
 static inline void inode_unlock(struct inode *inode)
 {
-       mutex_unlock(&inode->i_mutex);
+       up_write(&inode->i_rwsem);
+}
+
+static inline void inode_lock_shared(struct inode *inode)
+{
+       down_read(&inode->i_rwsem);
+}
+
+static inline void inode_unlock_shared(struct inode *inode)
+{
+       up_read(&inode->i_rwsem);
 }
 
 static inline int inode_trylock(struct inode *inode)
 {
-       return mutex_trylock(&inode->i_mutex);
+       return down_write_trylock(&inode->i_rwsem);
+}
+
+static inline int inode_trylock_shared(struct inode *inode)
+{
+       return down_read_trylock(&inode->i_rwsem);
 }
 
 static inline int inode_is_locked(struct inode *inode)
 {
-       return mutex_is_locked(&inode->i_mutex);
+       return rwsem_is_locked(&inode->i_rwsem);
 }
 
 static inline void inode_lock_nested(struct inode *inode, unsigned subclass)
 {
-       mutex_lock_nested(&inode->i_mutex, subclass);
+       down_write_nested(&inode->i_rwsem, subclass);
 }
 
 void lock_two_nondirectories(struct inode *, struct inode*);