linux-toradex.git/include/linux/kernfs.h, branch v6.3-rc5

kernfs: Implement kernfs_show()

2022-09-01T16:08:44+00:00

Currently, kernfs nodes can be created hidden and activated later by calling
kernfs_activate() to allow creation of multiple nodes to succeed or fail as
a unit. This is an one-way one-time-only transition. This patch introduces
kernfs_show() which can toggle visibility dynamically.

As the currently proposed use - toggling the cgroup pressure files - only
requires operating on leaf nodes, for the sake of simplicity, restrict it as
such for now.

Hiding uses the same mechanism as deactivation and likewise guarantees that
there are no in-flight operations on completion. KERNFS_ACTIVATED and
KERNFS_HIDDEN are used to manage the interactions between activations and
show/hide operations. A node is visible iff both activated & !hidden.

Cc: Chengming Zhou 
Cc: Johannes Weiner 
Tested-by: Chengming Zhou 
Reviewed-by: Chengming Zhou 
Signed-off-by: Tejun Heo 
Link: https://lore.kernel.org/r/20220828050440.734579-9-tj@kernel.org
Signed-off-by: Greg Kroah-Hartman

kernfs: Add KERNFS_REMOVING flags

2022-09-01T16:08:44+00:00

KERNFS_ACTIVATED tracks whether a given node has ever been activated. As a
node was only deactivated on removal, this was used for

 1. Drain optimization (removed by the previous patch).
 2. To hide !activated nodes
 3. To avoid double activations
 4. Reject adding children to a node being removed
 5. Skip activaing a node which is being removed.

We want to decouple deactivation from removal so that nodes can be
deactivated and hidden dynamically, which makes KERNFS_ACTIVATED useless for
all of the above purposes.

#1 is already gone. #2 and #3 can instead test whether the node is currently
active. A new flag KERNFS_REMOVING is added to explicitly mark nodes which
are being removed for #4 and #5.

While this leaves KERNFS_ACTIVATED with no users, leave it be as it will be
used in a following patch.

Cc: Chengming Zhou 
Tested-by: Chengming Zhou 
Reviewed-by: Chengming Zhou 
Signed-off-by: Tejun Heo 
Link: https://lore.kernel.org/r/20220828050440.734579-7-tj@kernel.org
Signed-off-by: Greg Kroah-Hartman

Revert "kernfs: Change kernfs_notify_list to llist."

2022-07-06T12:20:22+00:00

This reverts commit b8f35fa1188b84035c59d4842826c4e93a1b1c9f.

This is causing regression due to same kernfs_node getting
added multiple times in kernfs_notify_list so revert it until
safe way of using llist in this context is found.

Reported-by: Nathan Chancellor 
Reported-by: Michael Walle 
Reported-by: Marek Szyprowski 
Signed-off-by: Imran Khan 
Cc: Tejun Heo 
Link: https://lore.kernel.org/r/20220705201026.2487665-1-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman

kernfs: Replace global kernfs_open_file_mutex with hashed mutexes.

2022-06-27T14:46:15+00:00

In current kernfs design a single mutex, kernfs_open_file_mutex, protects
the list of kernfs_open_file instances corresponding to a sysfs attribute.
So even if different tasks are opening or closing different sysfs files
they can contend on osq_lock of this mutex. The contention is more apparent
in large scale systems with few hundred CPUs where most of the CPUs have
running tasks that are opening, accessing or closing sysfs files at any
point of time.

Using hashed mutexes in place of a single global mutex, can significantly
reduce contention around global mutex and hence can provide better
scalability. Moreover as these hashed mutexes are not part of kernfs_node
objects we will not see any singnificant change in memory utilization of
kernfs based file systems like sysfs, cgroupfs etc.

Modify interface introduced in previous patch to make use of hashed
mutexes. Use kernfs_node address as hashing key.

Acked-by: Tejun Heo 
Signed-off-by: Imran Khan 
Link: https://lore.kernel.org/r/20220615021059.862643-5-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman

kernfs: Change kernfs_notify_list to llist.

2022-06-27T14:46:15+00:00

At present kernfs_notify_list is implemented as a singly linked
list of kernfs_node(s), where last element points to itself and
value of ->attr.next tells if node is present on the list or not.
Both addition and deletion to list happen under kernfs_notify_lock.

Change kernfs_notify_list to llist so that addition to list can heppen
locklessly.

Suggested by: Al Viro 

Acked-by: Tejun Heo 
Signed-off-by: Imran Khan 
Link: https://lore.kernel.org/r/20220615021059.862643-3-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman

kernfs: make ->attr.open RCU protected.

2022-06-27T14:46:14+00:00

After removal of kernfs_open_node->refcnt in the previous patch,
kernfs_open_node_lock can be removed as well by making ->attr.open
RCU protected. kernfs_put_open_node can delegate freeing to ->attr.open
to RCU and other readers of ->attr.open can do so under rcu_read_(un)lock.

Suggested by: Al Viro 

Acked-by: Tejun Heo 
Signed-off-by: Imran Khan 
Link: https://lore.kernel.org/r/20220615021059.862643-2-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman

kernfs: remove unneeded #if 0 guard

2022-03-18T08:47:04+00:00

Commit f2eb478f2f32 ("kernfs: move struct kernfs_root out of the public
view.") moved kernfs_root out of kernfs.h, but my debugging code of a
 #if 0 was left in accidentally.  Fix that up by removing the guards.

Fixes: f2eb478f2f32 ("kernfs: move struct kernfs_root out of the public view.")
Cc: Tejun Heo 
Reported-by: Al Viro 
Link: https://lore.kernel.org/r/20220318073452.1486568-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman

kernfs: move struct kernfs_root out of the public view.

2022-02-23T14:46:34+00:00

There is no need to have struct kernfs_root be part of kernfs.h for
the whole kernel to see and poke around it.  Move it internal to kernfs
code and provide a helper function, kernfs_root_to_node(), to handle the
one field that kernfs users were directly accessing from the structure.

Cc: Imran Khan 
Acked-by: Tejun Heo 
Link: https://lore.kernel.org/r/20220222070713.3517679-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman

kernfs: Replace kernel.h with the necessary inclusions

2021-12-21T09:34:39+00:00

When kernel.h is used in the headers it adds a lot into dependency hell,
especially when there are circular dependencies are involved.

Replace kernel.h inclusion with the list of what is really being used.

Acked-by: Tejun Heo 
Signed-off-by: Andy Shevchenko 
Link: https://lore.kernel.org/r/20211209123008.3391-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman

kernfs: switch global kernfs_rwsem lock to per-fs lock

2021-11-24T12:55:16+00:00

The kernfs implementation has big lock granularity(kernfs_rwsem) so
every kernfs-based(e.g., sysfs, cgroup) fs are able to compete the
lock. It makes trouble for some cases to wait the global lock
for a long time even though they are totally independent contexts
each other.

A general example is process A goes under direct reclaim with holding
the lock when it accessed the file in sysfs and process B is waiting
the lock with exclusive mode and then process C is waiting the lock
until process B could finish the job after it gets the lock from
process A.

This patch switches the global kernfs_rwsem to per-fs lock, which
put the rwsem into kernfs_root.

Suggested-by: Tejun Heo 
Acked-by: Tejun Heo 
Signed-off-by: Minchan Kim 
Link: https://lore.kernel.org/r/20211118230008.2679780-1-minchan@kernel.org
Signed-off-by: Greg Kroah-Hartman