4.20-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dennis Krein <Dennis.Krein@xxxxxxxxxx> commit eb4c2382272ae7ae5d81fdfa5b7a6c86146eaaa4 upstream. 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@xxxxxxx> Reported-by: Christoph Hellwig <hch@xxxxxxxxxxxxx> Reported-by: Sebastian Kuzminsky <seb.kuzminsky@xxxxxxxxx> Signed-off-by: Dennis Krein <Dennis.Krein@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx> Tested-by: Dennis Krein <Dennis.Krein@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 4.16.x Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/rcu/srcutree.c | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -451,10 +451,12 @@ static void srcu_gp_start(struct srcu_st 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));
