tree 1c7a614250e370fc4d8341d2448c2e1acb7a42e8
parent 77da096d797033fe83bd5bf5b4e1ca774c50b0f4
author Ian Kent <raven@themaw.net> 1617965935 +0800
committer Ian Kent <raven@themaw.net> 1617965935 +0800

kernfs: use i_lock to protect concurrent inode updates

The inode operations .permission() and .getattr() use the kernfs node
write lock but all that's needed is to keep the rb tree stable while
updating the inode attributes as well as protecting the update itself
against concurrent changes.

And .permission() is called frequently during path walks and can cause
quite a bit of contention between kernfs node operations and path
walks when the number of concurrent walks is high.

To change kernfs_iop_getattr() and kernfs_iop_permission() to take
the rw sem read lock instead of the write lock an additional lock is
needed to protect against multiple processes concurrently updating
the inode attributes and link count in kernfs_refresh_inode().

The inode i_lock seems like the sensible thing to use to protect these
inode attribute updates so use it in kernfs_refresh_inode().

Signed-off-by: Ian Kent <raven@themaw.net>