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    SubjectRe: [PATCH v2 1/4] SUNRPC: release per-net clients lock before calling PipeFS dentries creation
    Date
    On Mon, 2012-02-27 at 19:50 +0400, Stanislav Kinsbursky wrote:
    > Lockdep is sad otherwise, because inode mutex is taken on PipeFS dentry
    > creation, which can be called on mount notification, where this per-net client
    > lock is taken on clients list walk.
    >
    > Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
    >
    > ---
    > net/sunrpc/clnt.c | 10 +++++++---
    > 1 files changed, 7 insertions(+), 3 deletions(-)
    >
    > diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
    > index bb7ed2f3..ddb5741 100644
    > --- a/net/sunrpc/clnt.c
    > +++ b/net/sunrpc/clnt.c
    > @@ -84,7 +84,7 @@ static void rpc_register_client(struct rpc_clnt *clnt)
    > struct sunrpc_net *sn = net_generic(clnt->cl_xprt->xprt_net, sunrpc_net_id);
    >
    > spin_lock(&sn->rpc_client_lock);
    > - list_add(&clnt->cl_clients, &sn->all_clients);
    > + list_add_tail(&clnt->cl_clients, &sn->all_clients);
    > spin_unlock(&sn->rpc_client_lock);
    > }
    >
    > @@ -208,15 +208,19 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
    > void *ptr)
    > {
    > struct super_block *sb = ptr;
    > - struct rpc_clnt *clnt;
    > + struct rpc_clnt *clnt, *tmp;
    > int error = 0;
    > struct sunrpc_net *sn = net_generic(sb->s_fs_info, sunrpc_net_id);
    >
    > spin_lock(&sn->rpc_client_lock);
    > - list_for_each_entry(clnt, &sn->all_clients, cl_clients) {
    > + list_for_each_entry_safe(clnt, tmp, &sn->all_clients, cl_clients) {
    > + atomic_inc(&clnt->cl_count);
    > + spin_unlock(&sn->rpc_client_lock);
    > error = __rpc_pipefs_event(clnt, event, sb);
    > + rpc_release_client(clnt);
    > if (error)
    > break;
    > + spin_lock(&sn->rpc_client_lock);
    > }
    > spin_unlock(&sn->rpc_client_lock);
    > return error;
    >

    This won't be safe. Nothing guarantees that 'tmp' remains valid after
    you drop the spin_lock.

    I think you rather need to add a check for whether clnt->cl_dentry is in
    the right state (NULL if RPC_PIPEFS_UMOUNT or non-NULL if
    RPC_PIPEFS_MOUNT) before deciding whether or not to atomic_inc() and
    drop the lock, so that you can restart the loop after calling
    __rpc_pipefs_event().


    --
    Trond Myklebust
    Linux NFS client maintainer

    NetApp
    Trond.Myklebust@netapp.com
    www.netapp.com

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