Messages in this thread | | | Date | Mon, 09 Sep 2013 13:56:50 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v4 1/1] dcache: Translating dentry into pathname without taking rename_lock |
| |
On 09/09/2013 01:45 PM, Linus Torvalds wrote: > On Mon, Sep 9, 2013 at 10:29 AM, Al Viro<viro@zeniv.linux.org.uk> wrote: >> I'm not sure I like mixing rcu_read_lock() into that - d_path() and friends >> can do that themselves just fine (it needs to be taken when seq is even), >> and e.g. d_walk() doesn't need it at all. Other than that, I'm OK with >> this variant. > Hmm.. I think you need the RCU read lock even when you get the write_seqlock(). > > Yes, getting the seqlock for write implies that you get a spinlock and > in many normal circumstances that basically is equvalent to being > rcu-locked, but afaik in some configurations that is *not* sufficient > protection against an RCU grace period on another CPU. You need to do > a real rcu_read_lock that increments that whole rcu_read_lock_nesting > level, which a spinlock won't do. > > And while the rename sequence lock protects against _renames_, it does > not protect against just plain dentries getting free'd under memory > pressure. > > So I think the RCU-readlockness really needs to be independent of the > sequence lock. > > Linus
Yes, you are right. It will be safer to take rcu_read_lock() even if we are taking the rename_lock. It wasn't needed before as d_lock was taken. Will update the patch to take rcu_read_lock() out to reflect that.
Regards, Longman
| |