On Thu, 2011-03-17 at 15:16 +0300, Stanislav Kinsbursky wrote:
> task->tk_waitqueue must be checked for NULL before trying to wake up task in
> rpc_killall_tasks() because it can be NULL.
>
> Here is an example:
>
> CPU 0 CPU 1 CPU 2
> -------------------- --------------------- --------------------------
> nfs4_run_open_task
> rpc_run_task
> rpc_execute
> rpc_set_active
> rpc_make_runnable
> (waiting)
> rpc_async_schedule
> nfs4_open_prepare
> nfs_wait_on_sequence
> nfs_umount_begin
> rpc_killall_tasks
> rpc_wake_up_task
> rpc_wake_up_queued_task
> spin_lock(tk_waitqueue == NULL)
> BUG()
> rpc_sleep_on
> spin_lock(&q->lock)
> __rpc_sleep_on
> task->tk_waitqueue = q
>
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@xxxxxxxxxx>
>
> ---
> net/sunrpc/clnt.c | 4 +++-
> 1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> index 57d344c..24039fe 100644
> --- a/net/sunrpc/clnt.c
> +++ b/net/sunrpc/clnt.c
> @@ -436,7 +436,9 @@ void rpc_killall_tasks(struct rpc_clnt *clnt)
> if (!(rovr->tk_flags & RPC_TASK_KILLED)) {
> rovr->tk_flags |= RPC_TASK_KILLED;
> rpc_exit(rovr, -EIO);
> - rpc_wake_up_queued_task(rovr->tk_waitqueue, rovr);
> + if (rovr->tk_waitqueue)
> + rpc_wake_up_queued_task(rovr->tk_waitqueue,
> + rovr);
Testing for RPC_IS_QUEUED(rovr) would be better, since that would
optimise away the call to rpc_wake_up_queued_task() altogether for those
tasks that aren't queued.
> }
> }
> spin_unlock(&clnt->cl_lock);
>
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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