scsi: bnx2fc: fix race condition in bnx2fc_get_host_stats()

If multiple tasks attempt to read the stats, it may happen that the
start_req_done completion is re-initialized while still being used by
another task, causing a list corruption.

This patch fixes the bug by adding a mutex to serialize the calls to
bnx2fc_get_host_stats().

WARNING: at lib/list_debug.c:48 list_del+0x6e/0xa0() (Not tainted)
Hardware name: PowerEdge R820
list_del corruption. prev->next should be ffff882035627d90, but was ffff884069541588

Pid: 40267, comm: perl Not tainted 2.6.32-642.3.1.el6.x86_64 #1
Call Trace:
 [<ffffffff8107c691>] ? warn_slowpath_common+0x91/0xe0
 [<ffffffff8107c796>] ? warn_slowpath_fmt+0x46/0x60
 [<ffffffff812ad16e>] ? list_del+0x6e/0xa0
 [<ffffffff81547eed>] ? wait_for_common+0x14d/0x180
 [<ffffffff8106c4a0>] ? default_wake_function+0x0/0x20
 [<ffffffff81547fd3>] ? wait_for_completion_timeout+0x13/0x20
 [<ffffffffa05410b1>] ? bnx2fc_get_host_stats+0xa1/0x280 [bnx2fc]
 [<ffffffffa04cf630>] ? fc_stat_show+0x90/0xc0 [scsi_transport_fc]
 [<ffffffffa04cf8b6>] ? show_fcstat_tx_frames+0x16/0x20 [scsi_transport_fc]
 [<ffffffff8137c647>] ? dev_attr_show+0x27/0x50
 [<ffffffff8113b9be>] ? __get_free_pages+0xe/0x50
 [<ffffffff812170e1>] ? sysfs_read_file+0x111/0x200
 [<ffffffff8119a305>] ? vfs_read+0xb5/0x1a0
 [<ffffffff8119b0b6>] ? fget_light_pos+0x16/0x50
 [<ffffffff8119a651>] ? sys_read+0x51/0xb0
 [<ffffffff810ee1fe>] ? __audit_syscall_exit+0x25e/0x290
 [<ffffffff8100b0d2>] ? system_call_fastpath+0x16/0x1b
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Acked-by: Chad Dupuis <chad.dupuis@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/bnx2fc/bnx2fc.h

@@ -191,6 +191,7 @@ struct bnx2fc_hba {
 	struct bnx2fc_cmd_mgr *cmd_mgr;
 	spinlock_t hba_lock;
 	struct mutex hba_mutex;
+	struct mutex hba_stats_mutex;
 	unsigned long adapter_state;
 		#define ADAPTER_STATE_UP		0
 		#define ADAPTER_STATE_GOING_DOWN	1

drivers/scsi/bnx2fc/bnx2fc_fcoe.c

@@ -663,15 +663,17 @@ static struct fc_host_statistics *bnx2fc_get_host_stats(struct Scsi_Host *shost)
 	if (!fw_stats)
 		return NULL;
 
+	mutex_lock(&hba->hba_stats_mutex);
+
 	bnx2fc_stats = fc_get_host_stats(shost);
 
 	init_completion(&hba->stat_req_done);
 	if (bnx2fc_send_stat_req(hba))
-		return bnx2fc_stats;
+		goto unlock_stats_mutex;
 	rc = wait_for_completion_timeout(&hba->stat_req_done, (2 * HZ));
 	if (!rc) {
 		BNX2FC_HBA_DBG(lport, "FW stat req timed out\n");
-		return bnx2fc_stats;
+		goto unlock_stats_mutex;
 	}
 	BNX2FC_STATS(hba, rx_stat2, fc_crc_cnt);
 	bnx2fc_stats->invalid_crc_count += hba->bfw_stats.fc_crc_cnt;
@@ -693,6 +695,9 @@ static struct fc_host_statistics *bnx2fc_get_host_stats(struct Scsi_Host *shost)
 
 	memcpy(&hba->prev_stats, hba->stats_buffer,
 	       sizeof(struct fcoe_statistics_params));
+
+unlock_stats_mutex:
+	mutex_unlock(&hba->hba_stats_mutex);
 	return bnx2fc_stats;
 }
 
@@ -1340,6 +1345,7 @@ static struct bnx2fc_hba *bnx2fc_hba_create(struct cnic_dev *cnic)
 	}
 	spin_lock_init(&hba->hba_lock);
 	mutex_init(&hba->hba_mutex);
+	mutex_init(&hba->hba_stats_mutex);
 
 	hba->cnic = cnic;