]> git.karo-electronics.de Git - linux-beck.git/commit
vfs: reimplement d_rcu_to_refcount() using lockref_get_or_lock()
authorLinus Torvalds <torvalds@linux-foundation.org>
Mon, 2 Sep 2013 18:38:06 +0000 (11:38 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Mon, 2 Sep 2013 18:38:06 +0000 (11:38 -0700)
commit15570086b590a69d59183b08a7770e316cca20a7
tree12c1494a59a3786bc99674567aa9b77af40a3698
parentdf3d0bbcdb2cafa23a70223d806655bd37e64a9b
vfs: reimplement d_rcu_to_refcount() using lockref_get_or_lock()

This moves __d_rcu_to_refcount() from <linux/dcache.h> into fs/namei.c
and re-implements it using the lockref infrastructure instead.  It also
adds a lot of comments about what is actually going on, because turning
a dentry that was looked up using RCU into a long-lived reference
counted entry is one of the more subtle parts of the rcu walk.

We also used to be _particularly_ subtle in unlazy_walk() where we
re-validate both the dentry and its parent using the same sequence
count.  We used to do it by nesting the locks and then verifying the
sequence count just once.

That was silly, because nested locking is expensive, but the sequence
count check is not.  So this just re-validates the dentry and the parent
separately, avoiding the nested locking, and making the lockref lookup
possible.

Acked-by: Waiman Long <waiman.long@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs/dcache.c
fs/namei.c
include/linux/dcache.h