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    SubjectRe: [PATCH v3 2/4] SUNRPC: fix races on PipeFS UMOUNT notifications
    25.06.2013 20:13, Myklebust, Trond пишет:
    > On Mon, 2013-06-24 at 11:52 +0400, Stanislav Kinsbursky wrote:
    >> CPU#0 CPU#1
    >> ----------------------------- -----------------------------
    >> rpc_kill_sb
    >> sn->pipefs_sb = NULL rpc_release_client
    >> (UMOUNT_EVENT) rpc_free_auth
    >> rpc_pipefs_event
    >> rpc_get_client_for_event
    >> !atomic_inc_not_zero(cl_count)
    >> <skip the client>
    >> atomic_inc(cl_count)
    >> rpc_free_client
    >> rpc_clnt_remove_pipedir
    >> <skip client dir removing>
    >>
    >> To fix this, this patch does the following:
    >>
    >> 1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
    >> 2) Removes SUNRPC client from the list AFTER pipes destroying.
    >> 3) Doesn't hold RPC client on notification: if client in the list, then it
    >> can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.
    >>
    >> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
    >> Cc: stable@vger.kernel.org
    >> ---
    >> net/sunrpc/clnt.c | 5 +----
    >> net/sunrpc/rpc_pipe.c | 2 +-
    >> 2 files changed, 2 insertions(+), 5 deletions(-)
    >
    > <snip>
    >
    >> diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
    >> index c512448..efca2f7 100644
    >> --- a/net/sunrpc/rpc_pipe.c
    >> +++ b/net/sunrpc/rpc_pipe.c
    >> @@ -1165,7 +1165,6 @@ static void rpc_kill_sb(struct super_block *sb)
    >> goto out;
    >> }
    >> sn->pipefs_sb = NULL;
    >> - mutex_unlock(&sn->pipefs_sb_lock);
    >> dprintk("RPC: sending pipefs UMOUNT notification for net %p%s\n",
    >> net, NET_NAME(net));
    >> blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
    >> @@ -1173,6 +1172,7 @@ static void rpc_kill_sb(struct super_block *sb)
    >> sb);
    >> put_net(net);
    >> out:
    >> + mutex_unlock(&sn->pipefs_sb_lock);
    >
    > Is this safe to do after the put_net()?
    >

    Sure it's not. Sorry.
    Will send the patch once more.

    >> kill_litter_super(sb);
    >> }
    >>
    >>
    >
    >


    --
    Best regards,
    Stanislav Kinsbursky
    --
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