Commit 25718fdc authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Jakub Kicinski
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net: gro_cells: Use nested-BH locking for gro_cell 



The gro_cell data structure is per-CPU variable and relies on disabled
BH for its locking. Without per-CPU locking in local_bh_disable() on
PREEMPT_RT this data structure requires explicit locking.

Add a local_lock_t to the data structure and use
local_lock_nested_bh() for locking. This change adds only lockdep
coverage and does not alter the functional behaviour for !PREEMPT_RT.

Reported-by: default avatar <syzbot+8715dd783e9b0bef43b1@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/68c6c3b1.050a0220.2ff435.0382.GAE@google.com/


Fixes: 3253cb49 ("softirq: Allow to drop the softirq-BKL lock on PREEMPT_RT")
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20251009094338.j1jyKfjR@linutronix.de


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent fcb8b32a

net/core/gro_cells.c

+10 −0
Original line number Diff line number Diff line
@@ -8,11 +8,13 @@ 
struct gro_cell {

	struct sk_buff_head	napi_skbs;

	struct napi_struct	napi;

	local_lock_t		bh_lock;

};



int gro_cells_receive(struct gro_cells *gcells, struct sk_buff *skb)

{

	struct net_device *dev = skb->dev;

	bool have_bh_lock = false;

	struct gro_cell *cell;

	int res;
@@ -25,6 +27,8 @@ int gro_cells_receive(struct gro_cells *gcells, struct sk_buff *skb) 
		goto unlock;

	}



	local_lock_nested_bh(&gcells->cells->bh_lock);

	have_bh_lock = true;

	cell = this_cpu_ptr(gcells->cells);



	if (skb_queue_len(&cell->napi_skbs) > READ_ONCE(net_hotdata.max_backlog)) {
@@ -39,6 +43,9 @@ int gro_cells_receive(struct gro_cells *gcells, struct sk_buff *skb) 
	if (skb_queue_len(&cell->napi_skbs) == 1)

		napi_schedule(&cell->napi);



	if (have_bh_lock)

		local_unlock_nested_bh(&gcells->cells->bh_lock);



	res = NET_RX_SUCCESS;



unlock:
@@ -54,6 +61,7 @@ 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) {

		skb = __skb_dequeue(&cell->napi_skbs);

		if (!skb)
@@ -64,6 +72,7 @@ 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;

}
@@ -79,6 +88,7 @@ int gro_cells_init(struct gro_cells *gcells, struct net_device *dev) 
		struct gro_cell *cell = per_cpu_ptr(gcells->cells, i);



		__skb_queue_head_init(&cell->napi_skbs);

		local_lock_init(&cell->bh_lock);



		set_bit(NAPI_STATE_NO_BUSY_POLL, &cell->napi.state);