On Wed, Dec 02, 2020 at 10:58:36PM +0800, Fox Chen wrote:
> A big global mutex in kernfs_iop_permission will significanly drag
> system performance when processes concurrently open files
> on kernfs in Big machines(with >= 16 cpu cores).
>
> This patch replace the big mutex with a rwlock specifically for
> protecting kernfs_node->iattribute. So that kernfs_iop_permission
> can perform concurrently.
>
> Signed-off-by: Fox Chen <foxhlc...@gmail.com>
> ---
> fs/kernfs/inode.c | 16 ++++++++--------
> include/linux/kernfs.h | 1 +
> 2 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
> index fc2469a20fed..c8c2ea669e6d 100644
> --- a/fs/kernfs/inode.c
> +++ b/fs/kernfs/inode.c
> @@ -106,9 +106,9 @@ int kernfs_setattr(struct kernfs_node *kn, const struct
> iattr *iattr)
> {
> int ret;
>
> - mutex_lock(&kernfs_mutex);
> + write_lock(&kn->iattr_rwlock);
> ret = __kernfs_setattr(kn, iattr);
> - mutex_unlock(&kernfs_mutex);
> + write_unlock(&kn->iattr_rwlock);
> return ret;
> }
>
> @@ -121,7 +121,7 @@ int kernfs_iop_setattr(struct dentry *dentry, struct
> iattr *iattr)
> if (!kn)
> return -EINVAL;
>
> - mutex_lock(&kernfs_mutex);
> + write_lock(&kn->iattr_rwlock);
> error = setattr_prepare(dentry, iattr);
> if (error)
> goto out;
> @@ -134,7 +134,7 @@ int kernfs_iop_setattr(struct dentry *dentry, struct
> iattr *iattr)
> setattr_copy(inode, iattr);
>
> out:
> - mutex_unlock(&kernfs_mutex);
> + write_unlock(&kn->iattr_rwlock);
> return error;
> }
>
> @@ -189,9 +189,9 @@ int kernfs_iop_getattr(const struct path *path, struct
> kstat *stat,
> struct inode *inode = d_inode(path->dentry);
> struct kernfs_node *kn = inode->i_private;
>
> - mutex_lock(&kernfs_mutex);
> + read_lock(&kn->iattr_rwlock);
> kernfs_refresh_inode(kn, inode);
> - mutex_unlock(&kernfs_mutex);
> + read_unlock(&kn->iattr_rwlock);
>
> generic_fillattr(inode, stat);
> return 0;
> @@ -281,9 +281,9 @@ int kernfs_iop_permission(struct inode *inode, int mask)
>
> kn = inode->i_private;
>
> - mutex_lock(&kernfs_mutex);
> + read_lock(&kn->iattr_rwlock);
> kernfs_refresh_inode(kn, inode);
> - mutex_unlock(&kernfs_mutex);
> + read_unlock(&kn->iattr_rwlock);
>
> return generic_permission(inode, mask);
> }
> diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
> index 89f6a4214a70..545cdb39b34b 100644
> --- a/include/linux/kernfs.h
> +++ b/include/linux/kernfs.h
> @@ -156,6 +156,7 @@ struct kernfs_node {
> unsigned short flags;
> umode_t mode;
> struct kernfs_iattrs *iattr;
> + rwlock_t iattr_rwlock;
> };
Don't you have to call rwlock_init() somewhere in order to properly
initialize the lock? Did you try running this under lockdep to ensure
that there are no issues?
thanks,
greg k-h
