scsi: bnx2fc: Make bnx2fc_recv_frame() mp safe

Running tests with a debug kernel shows that bnx2fc_recv_frame() is
modifying the per_cpu lport stats counters in a non-mpsafe way. Just boot
a debug kernel and run the bnx2fc driver with the hardware enabled.

[ 1391.699147] BUG: using smp_processor_id() in preemptible [00000000] code: bnx2fc_
[ 1391.699160] caller is bnx2fc_recv_frame+0xbf9/0x1760 [bnx2fc]
[ 1391.699174] CPU: 2 PID: 4355 Comm: bnx2fc_l2_threa Kdump: loaded Tainted: G B
[ 1391.699180] Hardware name: HP ProLiant DL120 G7, BIOS J01 07/01/2013
[ 1391.699183] Call Trace:
[ 1391.699188] dump_stack_lvl+0x57/0x7d
[ 1391.699198] check_preemption_disabled+0xc8/0xd0
[ 1391.699205] bnx2fc_recv_frame+0xbf9/0x1760 [bnx2fc]
[ 1391.699215] ? do_raw_spin_trylock+0xb5/0x180
[ 1391.699221] ? bnx2fc_npiv_create_vports.isra.0+0x4e0/0x4e0 [bnx2fc]
[ 1391.699229] ? bnx2fc_l2_rcv_thread+0xb7/0x3a0 [bnx2fc]
[ 1391.699240] bnx2fc_l2_rcv_thread+0x1af/0x3a0 [bnx2fc]
[ 1391.699250] ? bnx2fc_ulp_init+0xc0/0xc0 [bnx2fc]
[ 1391.699258] kthread+0x364/0x420
[ 1391.699263] ? _raw_spin_unlock_irq+0x24/0x50
[ 1391.699268] ? set_kthread_struct+0x100/0x100
[ 1391.699273] ret_from_fork+0x22/0x30

Restore the old get_cpu/put_cpu code with some modifications to reduce the
size of the critical section.

Link: https://lore.kernel.org/r/[e-mail]
Fixes: d576a5e80cd0 ("bnx2fc: Improve stats update mechanism")
Tested-by: Guangwu Zhang <[e-mail]>
Acked-by: Saurav Kashyap <[e-mail]>
Signed-off-by: John Meneghini <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/bnx2fc/bnx2fc_fcoe.c

···
 
 static void bnx2fc_recv_frame(struct sk_buff *skb)
 {
-	u32 fr_len;
+	u64 crc_err;
+	u32 fr_len, fr_crc;
 	struct fc_lport *lport;
 	struct fcoe_rcv_info *fr;
 	struct fc_stats *stats;
···
 	fh = (struct fc_frame_header *) skb_transport_header(skb);
 	skb_pull(skb, sizeof(struct fcoe_hdr));
 	fr_len = skb->len - sizeof(struct fcoe_crc_eof);
+
+	stats = per_cpu_ptr(lport->stats, get_cpu());
+	stats->RxFrames++;
+	stats->RxWords += fr_len / FCOE_WORD_TO_BYTE;
+	put_cpu();
 
 	fp = (struct fc_frame *)skb;
 	fc_frame_init(fp);
···
 		return;
 	}
 
-	stats = per_cpu_ptr(lport->stats, smp_processor_id());
-	stats->RxFrames++;
-	stats->RxWords += fr_len / FCOE_WORD_TO_BYTE;
+	fr_crc = le32_to_cpu(fr_crc(fp));
 
-	if (le32_to_cpu(fr_crc(fp)) !=
-			~crc32(~0, skb->data, fr_len)) {
-		if (stats->InvalidCRCCount < 5)
+	if (unlikely(fr_crc != ~crc32(~0, skb->data, fr_len))) {
+		stats = per_cpu_ptr(lport->stats, get_cpu());
+		crc_err = (stats->InvalidCRCCount++);
+		put_cpu();
+		if (crc_err < 5)
 			printk(KERN_WARNING PFX "dropping frame with "
 			       "CRC error\n");
-		stats->InvalidCRCCount++;
 		kfree_skb(skb);
 		return;
 	}