Commit d917c217 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Jakub Kicinski
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net: gro_cells: Reduce lock scope in gro_cell_poll 



One GRO-cell device's NAPI callback can nest into the GRO-cell of
another device if the underlying device is also using GRO-cell.
This is the case for IPsec over vxlan.
These two GRO-cells are separate devices. From lockdep's point of view
it is the same because each device is sharing the same lock class and so
it reports a possible deadlock assuming one device is nesting into
itself.

Hold the bh_lock only while accessing gro_cell::napi_skbs in
gro_cell_poll(). This reduces the locking scope and avoids acquiring the
same lock class multiple times.

Fixes: 25718fdc ("net: gro_cells: Use nested-BH locking for gro_cell")
Reported-by: default avatarGal Pressman <gal@nvidia.com>
Closes: https://lore.kernel.org/all/66664116-edb8-48dc-ad72-d5223696dd19@nvidia.com/


Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20251104153435.ty88xDQt@linutronix.de


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent b1d16f7c

net/core/gro_cells.c

+2 −2
Original line number Diff line number Diff line
@@ -60,9 +60,10 @@ static int gro_cell_poll(struct napi_struct *napi, int budget) 
	struct sk_buff *skb;

	int work_done = 0;



	__local_lock_nested_bh(&cell->bh_lock);

	while (work_done < budget) {

		__local_lock_nested_bh(&cell->bh_lock);

		skb = __skb_dequeue(&cell->napi_skbs);

		__local_unlock_nested_bh(&cell->bh_lock);

		if (!skb)

			break;

		napi_gro_receive(napi, skb);
@@ -71,7 +72,6 @@ static int gro_cell_poll(struct napi_struct *napi, int budget) 


	if (work_done < budget)

		napi_complete_done(napi, work_done);

	__local_unlock_nested_bh(&cell->bh_lock);

	return work_done;

}