sfc: extend the locking on mcdi->seqno

stable inclusion
from stable-v5.10.107
commit 2490695ffdbafbe79fb9c204df33a4597b1473b4
bugzilla: https://gitee.com/openeuler/kernel/issues/I574A2

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2490695ffdbafbe79fb9c204df33a4597b1473b4

--------------------------------

[ Upstream commit f1fb205e ]

seqno could be read as a stale value outside of the lock. The lock is
already acquired to protect the modification of seqno against a possible
race condition. Place the reading of this value also inside this locking
to protect it against a possible race condition.
Signed-off-by: NNiels Dossche <dossche.niels@gmail.com>
Acked-by: NMartin Habets <habetsm.xilinx@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/net/ethernet/sfc/mcdi.c

@@ -163,9 +163,9 @@ static void efx_mcdi_send_request(struct efx_nic *efx, unsigned cmd,
 	/* Serialise with efx_mcdi_ev_cpl() and efx_mcdi_ev_death() */
 	spin_lock_bh(&mcdi->iface_lock);
 	++mcdi->seqno;
+	seqno = mcdi->seqno & SEQ_MASK;
 	spin_unlock_bh(&mcdi->iface_lock);
 
-	seqno = mcdi->seqno & SEQ_MASK;
 	xflags = 0;
 	if (mcdi->mode == MCDI_MODE_EVENTS)
 		xflags |= MCDI_HEADER_XFLAGS_EVREQ;