On Thu, 2011-03-17 at 18:43 +0300, Stanislav Kinsbursky wrote:
> 17.03.2011 16:01, Trond Myklebust ÐÐÑÐÑ:
> > 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.
> >
>
> Yes, I agree with testing RPC_IS_QUEUED(rovr) since such approach looks
> clearer and in 2.6.38 tk_waitqueue is initialized prior to set
> RPC_TASK_QUEUED bit.
> But I found this problem in 2.6.32 rhel kernel where this set sequence is inversed.
> Will send fixed version soon.
Are you sure? Why would the 2.6.32 rhel kernel differ from the mainline
2.6.32 kernel in this respect?
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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