Commit eb4c2382 authored Oct 26, 2018 by Dennis Krein Committed by Paul E. McKenney Nov 27, 2018

srcu: Lock srcu_data structure in srcu_gp_start()



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> # 4.16.x

parent 0607ba84

kernel/rcu/srcutree.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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));

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