From: "J. Bruce Fields" <bfields@xxxxxxxxxx> We add the new state to the nfsi->open_states list, making it potentially visible to other threads, before we've finished initializing it. That wasn't a problem when all the readers were also taking the i_lock (as we do here), but since we switched to RCU, there's now a possibility that a reader could see the partially initialized state. Symptoms observed were a crash when another thread called nfs4_get_valid_delegation() on a NULL inode, resulting in an oops like: BUG: unable to handle page fault for address: ffffffffffffffb0 ... RIP: 0010:nfs4_get_valid_delegation+0x6/0x30 [nfsv4] ... Call Trace: nfs4_open_prepare+0x80/0x1c0 [nfsv4] __rpc_execute+0x75/0x390 [sunrpc] ? finish_task_switch+0x75/0x260 rpc_async_schedule+0x29/0x40 [sunrpc] process_one_work+0x1ad/0x370 worker_thread+0x30/0x390 ? create_worker+0x1a0/0x1a0 kthread+0x10c/0x130 ? kthread_park+0x80/0x80 ret_from_fork+0x22/0x30 Fixes: 9ae075fdd190 "NFSv4: Convert open state lookup to use RCU" Reviewed-by: Seiichi Ikarashi <s.ikarashi@xxxxxxxxxxx> Tested-by: Daisuke Matsuda <matsuda-daisuke@xxxxxxxxxxx> Tested-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx> --- fs/nfs/nfs4state.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) > I do have a patch including the tags and oops provided by Masayoshi > Mizuma, if you'd like to take that instead. See followup.--b. Here you go. diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c index f7723d221945..459c7fb5d103 100644 --- a/fs/nfs/nfs4state.c +++ b/fs/nfs/nfs4state.c @@ -734,9 +734,9 @@ nfs4_get_open_state(struct inode *inode, struct nfs4_state_owner *owner) state = new; state->owner = owner; atomic_inc(&owner->so_count); - list_add_rcu(&state->inode_states, &nfsi->open_states); ihold(inode); state->inode = inode; + list_add_rcu(&state->inode_states, &nfsi->open_states); spin_unlock(&inode->i_lock); /* Note: The reclaim code dictates that we add stateless * and read-only stateids to the end of the list */ -- 2.26.2
