Hi,
This started as a bug report by Hillf Danton and aims to access
kernfs_node::{name|parent} with RCU to avoid the lock during
kernfs_path_from_node().
I've split the individual fixes in separate patches (#1 to #4). I've
also split the ::parent and ::name RCU conversation into a single patch
(#5 and #6).
v4…v5 https://lore.kernel.org/all/20250124174614.866884-1-bigeasy@xxxxxxxxxxxxx/
- rdtgroup:
- Add a comment to rdt_get_kn_parent_priv() regarding lifetime of
parent.
- Move individual rcu_dereference_check() invocations into
rdt_kn_parent() with a comment on lifetime.
- Use rcu_access_pointer() in kernfs_to_rdtgroup() instead
rcu_dereference_check(, true)
- s/kernfs_rcu_get_name/kernfs_rcu_name/
- Move all rcu_dereference_check() within kernfs into kernfs_parent()
and extend its checks to have all cases in one spot. Document why
each case makes sense.
- kernfs_notify_workfn(): Do unlocks in the reverse order of locks.
- Add kernfs_root_flags() and use it in cgroup's kn_get_priv() to
check the right KERNFS_ROOT_INVARIANT_PARENT flag.
v3: https://lore.kernel.org/all/20241121175250.EJbI7VMb@xxxxxxxxxxxxx/
v2: https://lore.kernel.org/all/20241112155713.269214-1-bigeasy@xxxxxxxxxxxxx/
v1: https://lore.kernel.org/all/20241108222406.n5azgO98@xxxxxxxxxxxxx/
Sebastian
Sebastian Andrzej Siewior (6):
kernfs: Acquire kernfs_rwsem in kernfs_notify_workfn().
kernfs: Acquire kernfs_rwsem in kernfs_get_parent_dentry().
kernfs: Acquire kernfs_rwsem in kernfs_node_dentry().
kernfs: Don't re-lock kernfs_root::kernfs_rwsem in
kernfs_fop_readdir().
kernfs: Use RCU to access kernfs_node::parent.
kernfs: Use RCU to access kernfs_node::name.
arch/x86/kernel/cpu/resctrl/internal.h | 5 +
arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 14 +-
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 73 +++++---
fs/kernfs/dir.c | 214 ++++++++++++----------
fs/kernfs/file.c | 6 +-
fs/kernfs/kernfs-internal.h | 37 +++-
fs/kernfs/mount.c | 21 ++-
fs/kernfs/symlink.c | 30 +--
fs/sysfs/dir.c | 2 +-
fs/sysfs/file.c | 24 ++-
include/linux/kernfs.h | 14 +-
kernel/cgroup/cgroup-v1.c | 2 +-
kernel/cgroup/cgroup.c | 24 ++-
security/selinux/hooks.c | 7 +-
14 files changed, 306 insertions(+), 167 deletions(-)
--
2.47.2
