On 2015/3/16 14:02, Valdis.Kletnieks@xxxxxx wrote: > On Mon, 16 Mar 2015 10:06:37 +0800, Lee said: > >> I am studying the dcache in VFS recently . I found that hlist of dcache >> is already protected by RCU in >> __d_lookup.Is it necessary for the function -- d_lookup using >> sequence lock to protect the hlist again? > > RCU is useful when you can tolerate a bit of latency in other users > finding out about updated values and/or slightly stale values. That's > not an option for d_lookup(), which has to check the most recent value > in order to avoid race conditions. > In __d_lookup(), one hlist is protected well with RCU. But this is not enough for the dentry_hashtable, so d_lookup() uses some mechanism to protect the dentry_hashtable, in this condition, the mechanism is sequence lock :-) _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
