On Mon, Sep 17, 2012 at 12:40:16PM -0700, Tejun Heo wrote:

On Fri, Sep 14, 2012 at 03:50:40PM -0700, Colin Cross wrote:

quoted

This patch set fixes a reproducible crash I'm seeing on a 3.4.10
kernel.  flush_kthread_worker (which is different from
flush_kthread_work) is initializing a kthread_work and a completion on
the stack, then queuing it and calling wait_for_completion.  Once the
completion is signaled, flush_kthread_worker exits and the stack
region used by the kthread_work may be immediately reused by another
object on the stack, but kthread_worker_fn continues accessing its
work pointer:
                work->func(work);         <- calls complete,
effectively frees work
                smp_wmb();      /* wmb worker-b0 paired with flush-b1 */
                work->done_seq = work->queue_seq;   <- overwrites a
new stack object
                smp_mb();       /* mb worker-b1 paired with flush-b0 */
                if (atomic_read(&work->flushing))
                        wake_up_all(&work->done);  <- or crashes here

These patches fix the problem by not accessing work after work->func
is called, and should be backported to stable.  They apply cleanly to
3.4.10.  Upstream commits are 9a2e03d8ed518a61154f18d83d6466628e519f94
and 46f3d976213452350f9d10b0c2780c2681f7075b.

Yeah, you're right.  I wonder why this didn't come up before.  Greg,
can you please pick up these two commits?

Ok, will do, thanks for letting me know.

greg k-h