Re: [1/1] libceph: use RCU to protect monmap in ceph_compare_options()

Hi Ren,

NACK for now. Thanks for the patch, but I have some concerns
that need a v2:

  1. [major] net/ceph/mon_client.c:1032: Raw __rcu dereference in do_mon_command()
     `h->fsid = monc->monmap->fsid;` is a raw dereference of the
     now-`__rcu` pointer. The identical pattern in `ceph_monc_do_statfs`
     was converted but this one was missed. Safe (under `monc->mutex`),
     but sparse will warn and the conversion is inconsistent.
     Suggested fix: Use `rcu_dereference_protected(monc->monmap,
     lockdep_is_held(&monc->mutex))`, same as the other mutex-protected
     sites.
  2. [major] net/ceph/ceph_common.c:806: Raw __rcu dereference in wait_for_setup path
     `have_monmap = client->monc.monmap && client->monc.monmap->epoch;`
     — two raw accesses to the `__rcu` pointer. Under `monc->mutex`, so
     safe, but sparse will flag it.
     Suggested fix: Same `rcu_dereference_protected()` pattern.
  3. [minor] net/ceph/mon_client.c:1175: Init-path assignment to __rcu pointer without RCU_INIT_POINTER
  4. [nit] commit message: Non-standard Assisted-by trailer tag

RCU approach is correct but __rcu annotation conversion is incomplete — at least two mutex-protected sites still dereference raw, which will produce sparse warnings.


-- 
Alex Markuze