[PATCH] powerpc/qspinlock: Fix deadlock in MCS queue

[Michael Ellerman]

"Nysal Jan K.A." <nysal at linux.ibm.com> writes:
> If an interrupt occurs in queued_spin_lock_slowpath() after we increment
> qnodesp->count and before node->lock is initialized, another CPU might
> see stale lock values in get_tail_qnode(). If the stale lock value happens
> to match the lock on that CPU, then we write to the "next" pointer of
> the wrong qnode. This causes a deadlock as the former CPU, once it becomes
> the head of the MCS queue, will spin indefinitely until it's "next" pointer
> is set by its successor in the queue. This results in lockups similar to
> the following.
...
>
> Thanks to Saket Kumar Bhaskar for help with recreating the issue
>
> Fixes: 84990b169557 ("powerpc/qspinlock: add mcs queueing for contended waiters")
> Cc: stable at vger.kernel.org # v6.2+
> Reported-by: Geetika Moolchandani <geetika at linux.ibm.com>
> Reported-by: Vaishnavi Bhat <vaish123 at in.ibm.com>
> Reported-by: Jijo Varghese <vargjijo at in.ibm.com>
 
Do we have links for any of these reports?

cheers