[PATCH] libata:fix kernel panic when hotplug

[DingXiang]

In normal condition,if we use sas protocol and hotplug a sata disk on a port,
the sas driver will send event "PORTE_BYTES_DMAED" and call function "sas_porte_bytes_dmaed".
But if a sata disk is run io and unplug it,then plug a new sata disk,this operation may cause
a kernel panic like this:
[ 2366.923208] Unable to handle kernel NULL pointer dereference at virtual address 000007b8
[ 2366.949253] pgd = ffffffc00121d000
[ 2366.971164] [000007b8] *pgd=00000027df893003, *pud=00000027df893003, *pmd=00000027df894003, *pte=006000006d000707
[ 2367.022822] Internal error: Oops: 96000005 [#1] SMP
[ 2367.048490] Modules linked in: dm_mirror(E) dm_region_hash(E) dm_log(E) dm_mod(E) crc32_arm64(E) aes_ce_blk(E) ablk_helper(E) cryptd(E) aes_ce_cipher(E) ghash_ce(E) sha2_ce(E) sha1_ce(E) ses(E) enclosure(E) shpchp(E) marvell(E)
[ 2367.144808] CPU: 16 PID: 710 Comm: kworker/16:1 Tainted: G            E   4.1.23-next.aarch64 #1
[ 2367.180161] Hardware name: Huawei Taishan 2280 /BC11SPCC, BIOS 1.28 05/14/2016
[ 2367.213305] Workqueue: events ata_scsi_hotplug
[ 2367.244296] task: ffffffe7db9b5e00 ti: ffffffe7db1a0000 task.ti: ffffffe7db1a0000
[ 2367.279949] PC is at sas_find_dev_by_rphy+0x48/0x118
[ 2367.312045] LR is at sas_find_dev_by_rphy+0x40/0x118
[ 2367.341970] pc : [<ffffffc00065c3b0>] lr : [<ffffffc00065c3a8>] pstate: 00000145
...
[ 2368.766334] Call trace:
[ 2368.781712] [<ffffffc00065c3b0>] sas_find_dev_by_rphy+0x48/0x118
[ 2368.800394] [<ffffffc00065c4a8>] sas_target_alloc+0x28/0x98
[ 2368.817975] [<ffffffc00063e920>] scsi_alloc_target+0x248/0x308
[ 2368.835570] [<ffffffc000640080>] __scsi_add_device+0xb8/0x160
[ 2368.853034] [<ffffffc0006e52d8>] ata_scsi_scan_host+0x190/0x230
[ 2368.871614] [<ffffffc0006e54b0>] ata_scsi_hotplug+0xc8/0xe8
[ 2368.889152] [<ffffffc0000da75c>] process_one_work+0x164/0x438
[ 2368.908003] [<ffffffc0000dab74>] worker_thread+0x144/0x4b0
[ 2368.924613] [<ffffffc0000e0ffc>] kthread+0xfc/0x110
[ 2368.940923] Code: aa1303e0 97ff5deb 34ffff80 d1082273 (f943de76)

This because "dev_to_shost" in "sas_find_dev_by_rphy" return a NULL point,and SHOST_TO_SAS_HA used it,so kernel panic happed.

why dev_to_shost return a NULL point?
  Because in "__scsi_add_device" ,struct device *parent = &shost->shost_gendev,and in "scsi_alloc_target", "*parent" is
assigned to "starget->dev.parent",then "sas_target_alloc" will get "struct sas_rphy" according "starget->dev.parent",
and  in "sas_find_dev_by_rphy" , we will get "struct Scsi_Host *shost" acording "rphy->dev.parent",we will find that 
rphy->dev.parent = shost->shost_gendev.parent, and shost_gendev.parent is "ap->tdev",there is no parent any more,so "dev_to_shost"
return a NULL point.

when the panic will happen?
  When libata is handling error,and add hotplug_task to workqueue,
if a new sata disk pluged at the same time,the libata hotplug task will run and panic will happen.

In fact,we don't need libata to deal with hotplug in sas enviroment.So we can't run ata hotplug task when ata port is sas host.

Signed-off-by:Dingxiang <dingxiang@xxxxxxxxxx>
Signed-off-by:Chenqilin <chenqilin2@xxxxxxxxxx>
---
 drivers/ata/libata-eh.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 961acc7..74c5ecf 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -816,8 +816,11 @@ void ata_scsi_port_error_handler(struct Scsi_Host *host, struct ata_port *ap)
 
 	if (ap->pflags & ATA_PFLAG_LOADING)
 		ap->pflags &= ~ATA_PFLAG_LOADING;
-	else if (ap->pflags & ATA_PFLAG_SCSI_HOTPLUG)
-		schedule_delayed_work(&ap->hotplug_task, 0);
+	else if (ap->pflags & ATA_PFLAG_SCSI_HOTPLUG){
+		if(ap->flags & ATA_FLAG_SAS_HOST)
+			ap->pflags &= ~ATA_PFLAG_SCSI_HOTPLUG;
+		else
+			schedule_delayed_work(&ap->hotplug_task, 0);
 
 	if (ap->pflags & ATA_PFLAG_RECOVERED)
 		ata_port_info(ap, "EH complete\n");
-- 
1.7.1