On Thu, Apr 25, 2019 at 04:02:11PM +0100, David Howells wrote: > Allow searching of the inode cache under RCU conditions - but with a > footnote that this is redone under lock under certain conditions. > > The following changes are made: > > (1) Use hlist_add_head_rcu() and hlist_del_init_rcu() to add and remove > an inode to/from a bucket. > > (2) In rehash_inode(), called by Coda to change the identifying parameters > on an inode during resolution of disconnected operation, lock > inode_hash_lock with write_seqlock(), which takes the spinlock and > bumps the sequence counter. > > (3) Provide __find_inode_rcu() and __find_inode_by_ino rcu() which do an > RCU-safe crawl through a hash bucket. > > (4) Provide find_inode_rcu() and find_inode_by_ino_rcu() which do a > read_seqbegin_or_lock() conditional lock-loop on inode_hash_lock to > cover searching the icache. Normally this will work without needing > to retry, but in case (4), where an inode may be moved between lists, > we need to retry with the lock held. Hmm... Why do these stores to ->i_state need WRITE_ONCE, while an arseload of similar in fs/fs-writeback.c does not?
