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Date: Fri, 15 Apr 2016 21:02:06 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: Al Viro <viro@...IV.linux.org.uk>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 15/15] parallel lookups: actual switch to rwsem
On Apr 15, 2016, at 6:55 PM, Al Viro <viro@...IV.linux.org.uk> wrote:
>
> From: Al Viro <viro@...iv.linux.org.uk>
>
> 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@...iv.linux.org.uk>
> ---
> fs/btrfs/ioctl.c | 16 ++++++++++------
> fs/configfs/inode.c | 2 +-
> fs/dcache.c | 9 +++++----
> fs/gfs2/ops_fstype.c | 2 +-
> fs/inode.c | 12 ++++++------
> fs/namei.c | 4 ++--
> fs/ocfs2/inode.c | 2 +-
> fs/overlayfs/readdir.c | 4 +++-
> fs/readdir.c | 7 ++++---
> include/linux/fs.h | 12 ++++++------
> 10 files changed, 39 insertions(+), 31 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 053e677..db1e830 100644
> --- 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);
> diff --git a/fs/configfs/inode.c b/fs/configfs/inode.c
> index 03d124a..0387968 100644
> --- 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 5965588..d110040 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -2911,7 +2911,8 @@ 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 */
> @@ -2922,15 +2923,15 @@ 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 (!down_read_trylock(&alias->d_parent->d_inode->i_rwsem))
> 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
> --- 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
> --- 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 eb879d6..877e9ef 100644
> --- 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);
> + down_read(&inode->i_rwsem);
Wouldn't it make sense to have helpers like "inode_read_lock(inode)" or similar,
so that it is consistent with other parts of the code and easier to find?
It's a bit strange to have the filesystems use "inode_lock()" and some places
here use "inode_lock_nested()", but other places use up_read() and down_read()
directly on &inode->i_rwsem. That would also simplify delegating the directory
locking to the filesystems in the future.
Cheers, Andreas
> /* 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);
> + up_read(&inode->i_rwsem);
> return dentry;
> }
>
> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
> index 12f4a9e..0748777 100644
> --- 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
> --- 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
> --- 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 0a32045..313ad28 100644
> --- 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 +734,27 @@ 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 int inode_trylock(struct inode *inode)
> {
> - return mutex_trylock(&inode->i_mutex);
> + return down_write_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*);
> --
> 2.8.0.rc3
>
> --
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Cheers, Andreas
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