From: Dennis Krein Dennis.Krein@netapp.com

The srcu_gp_start() function is called with the srcu_struct structure's ->lock held, but not with the srcu_data structure's ->lock. This is problematic because this function accesses and updates the srcu_data structure's ->srcu_cblist, which is protected by that lock. Failing to hold this lock can result in corruption of the SRCU callback lists, which in turn can result in arbitrarily bad results.

This commit therefore makes srcu_gp_start() acquire the srcu_data structure's ->lock across the calls to rcu_segcblist_advance() and rcu_segcblist_accelerate(), thus preventing this corruption.

Reported-by: Bart Van Assche bvanassche@acm.org Reported-by: Christoph Hellwig hch@infradead.org Reported-by: Sebastian Kuzminsky seb.kuzminsky@gmail.com Signed-off-by: Dennis Krein Dennis.Krein@netapp.com Signed-off-by: Paul E. McKenney paulmck@linux.ibm.com Tested-by: Dennis Krein Dennis.Krein@netapp.com Cc: stable@vger.kernel.org # 4.12.x --- kernel/rcu/srcutree.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 60f3236beaf7..697a2d7e8e8a 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -451,10 +451,12 @@ static void srcu_gp_start(struct srcu_struct *sp)

lockdep_assert_held(&ACCESS_PRIVATE(sp, lock)); WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)); + spin_lock_rcu_node(sdp); /* Interrupts already disabled. */ rcu_segcblist_advance(&sdp->srcu_cblist, rcu_seq_current(&sp->srcu_gp_seq)); (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, rcu_seq_snap(&sp->srcu_gp_seq)); + spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */ smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */ rcu_seq_start(&sp->srcu_gp_seq); state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq));