Ian Kent <raven@xxxxxxxxxx> writes:
> The kernfs global lock restricts the ability to perform kernfs node
> lookup operations in parallel during path walks.
>
> Change the kernfs mutex to an rwsem so that, when opportunity arises,
> node searches can be done in parallel with path walk lookups.
>
> Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
> ---
> fs/kernfs/dir.c | 117 ++++++++++++++++++++++++-------------------
> fs/kernfs/file.c | 4 +
> fs/kernfs/inode.c | 16 +++---
> fs/kernfs/kernfs-internal.h | 5 +-
> fs/kernfs/mount.c | 12 ++--
> fs/kernfs/symlink.c | 4 +
> include/linux/kernfs.h | 2 -
> 7 files changed, 86 insertions(+), 74 deletions(-)
>
> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> index 5151c712f06f5..1e2e35a201dfb 100644
> --- a/fs/kernfs/dir.c
> +++ b/fs/kernfs/dir.c
> @@ -17,7 +17,7 @@
>
> #include "kernfs-internal.h"
>
> -DEFINE_MUTEX(kernfs_mutex);
> +DECLARE_RWSEM(kernfs_rwsem);
> static DEFINE_SPINLOCK(kernfs_rename_lock); /* kn->parent and ->name */
> static char kernfs_pr_cont_buf[PATH_MAX]; /* protected by rename_lock */
> static DEFINE_SPINLOCK(kernfs_idr_lock); /* root->ino_idr */
> @@ -26,10 +26,21 @@ static DEFINE_SPINLOCK(kernfs_idr_lock); /* root->ino_idr */
>
> static bool kernfs_active(struct kernfs_node *kn)
> {
> - lockdep_assert_held(&kernfs_mutex);
> return atomic_read(&kn->active) >= 0;
> }
>
> +static bool kernfs_active_write(struct kernfs_node *kn)
> +{
> + lockdep_assert_held_write(&kernfs_rwsem);
> + return kernfs_active(kn);
> +}
> +
> +static bool kernfs_active_read(struct kernfs_node *kn)
> +{
> + lockdep_assert_held_read(&kernfs_rwsem);
> + return kernfs_active(kn);
> +}
This bit is unnecessary and confusing. There is nothing read/write
about how the kernfs file is active (aka being used be a function).
Further all that is needed for correct operation is:
> static bool kernfs_active(struct kernfs_node *kn)
> {
> - lockdep_assert_held(&kernfs_mutex);
> + lockdep_assert_held(&kernfs_rwsem);
> return atomic_read(&kn->active) >= 0;
> }
Eric
