[PATCH 3.13 169/259] libata: introduce ata_host->n_tags to avoid oops on SAS controllers

From: Kamal Mostafa
Date: Fri Aug 08 2014 - 16:44:59 EST

3.13.11.6 -stable review patch. If anyone has any objections, please let me know.

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

From: Tejun Heo <tj@xxxxxxxxxx>

commit 1a112d10f03e83fb3a2fdc4c9165865dec8a3ca6 upstream.

1871ee134b73 ("libata: support the ata host which implements a queue
depth less than 32") directly used ata_port->scsi_host->can_queue from
ata_qc_new() to determine the number of tags supported by the host;
unfortunately, SAS controllers doing SATA don't initialize ->scsi_host
leading to the following oops.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
IP: [<ffffffff814e0618>] ata_qc_new_init+0x188/0x1b0
PGD 0
Oops: 0002 [#1] SMP
Modules linked in: isci libsas scsi_transport_sas mgag200 drm_kms_helper ttm
CPU: 1 PID: 518 Comm: udevd Not tainted 3.16.0-rc6+ #62
Hardware name: Intel Corporation S2600CO/S2600CO, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013
task: ffff880c1a00b280 ti: ffff88061a000000 task.ti: ffff88061a000000
RIP: 0010:[<ffffffff814e0618>] [<ffffffff814e0618>] ata_qc_new_init+0x188/0x1b0
RSP: 0018:ffff88061a003ae8 EFLAGS: 00010012
RAX: 0000000000000001 RBX: ffff88000241ca80 RCX: 00000000000000fa
RDX: 0000000000000020 RSI: 0000000000000020 RDI: ffff8806194aa298
RBP: ffff88061a003ae8 R08: ffff8806194a8000 R09: 0000000000000000
R10: 0000000000000000 R11: ffff88000241ca80 R12: ffff88061ad58200
R13: ffff8806194aa298 R14: ffffffff814e67a0 R15: ffff8806194a8000
FS: 00007f3ad7fe3840(0000) GS:ffff880627620000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000058 CR3: 000000061a118000 CR4: 00000000001407e0
Stack:
ffff88061a003b20 ffffffff814e96e1 ffff88000241ca80 ffff88061ad58200
ffff8800b6bf6000 ffff880c1c988000 ffff880619903850 ffff88061a003b68
ffffffffa0056ce1 ffff88061a003b48 0000000013d6e6f8 ffff88000241ca80
Call Trace:
[<ffffffff814e96e1>] ata_sas_queuecmd+0xa1/0x430
[<ffffffffa0056ce1>] sas_queuecommand+0x191/0x220 [libsas]
[<ffffffff8149afee>] scsi_dispatch_cmd+0x10e/0x300
[<ffffffff814a3bc5>] scsi_request_fn+0x2f5/0x550
[<ffffffff81317613>] __blk_run_queue+0x33/0x40
[<ffffffff8131781a>] queue_unplugged+0x2a/0x90
[<ffffffff8131ceb4>] blk_flush_plug_list+0x1b4/0x210
[<ffffffff8131d274>] blk_finish_plug+0x14/0x50
[<ffffffff8117eaa8>] __do_page_cache_readahead+0x198/0x1f0
[<ffffffff8117ee21>] force_page_cache_readahead+0x31/0x50
[<ffffffff8117ee7e>] page_cache_sync_readahead+0x3e/0x50
[<ffffffff81172ac6>] generic_file_read_iter+0x496/0x5a0
[<ffffffff81219897>] blkdev_read_iter+0x37/0x40
[<ffffffff811e307e>] new_sync_read+0x7e/0xb0
[<ffffffff811e3734>] vfs_read+0x94/0x170
[<ffffffff811e43c6>] SyS_read+0x46/0xb0
[<ffffffff811e33d1>] ? SyS_lseek+0x91/0xb0
[<ffffffff8171ee29>] system_call_fastpath+0x16/0x1b
Code: 00 00 00 88 50 29 83 7f 08 01 19 d2 83 e2 f0 83 ea 50 88 50 34 c6 81 1d 02 00 00 40 c6 81 17 02 00 00 00 5d c3 66 0f 1f 44 00 00 <89> 14 25 58 00 00 00

Fix it by introducing ata_host->n_tags which is initialized to
ATA_MAX_QUEUE - 1 in ata_host_init() for SAS controllers and set to
scsi_host_template->can_queue in ata_host_register() for !SAS ones.
As SAS hosts are never registered, this will give them the same
ATA_MAX_QUEUE - 1 as before. Note that we can't use
scsi_host->can_queue directly for SAS hosts anyway as they can go
higher than the libata maximum.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Mike Qiu <qiudayu@xxxxxxxxxxxxxxxxxx>
Reported-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
Reported-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Reported-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Tested-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
Fixes: 1871ee134b73 ("libata: support the ata host which implements a queue depth less than 32")
Cc: Kevin Hao <haokexin@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
drivers/ata/libata-core.c | 16 ++++------------
include/linux/libata.h | 1 +
2 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 0172e30..f761603 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4798,9 +4798,8 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
{
struct ata_queued_cmd *qc = NULL;
- unsigned int i, tag, max_queue;
-
- max_queue = ap->scsi_host->can_queue;
+ unsigned int max_queue = ap->host->n_tags;
+ unsigned int i, tag;

/* no command while frozen */
if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
@@ -6109,6 +6108,7 @@ void ata_host_init(struct ata_host *host, struct device *dev,
{
spin_lock_init(&host->lock);
mutex_init(&host->eh_mutex);
+ host->n_tags = ATA_MAX_QUEUE - 1;
host->dev = dev;
host->ops = ops;
}
@@ -6190,15 +6190,7 @@ int ata_host_register(struct ata_host *host, struct scsi_host_template *sht)
{
int i, rc;

- /*
- * The max queue supported by hardware must not be greater than
- * ATA_MAX_QUEUE.
- */
- if (sht->can_queue > ATA_MAX_QUEUE) {
- dev_err(host->dev, "BUG: the hardware max queue is too large\n");
- WARN_ON(1);
- return -EINVAL;
- }
+ host->n_tags = clamp(sht->can_queue, 1, ATA_MAX_QUEUE - 1);

/* host must have been started */
if (!(host->flags & ATA_HOST_STARTED)) {
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 3fee55e..e13b3ae 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -593,6 +593,7 @@ struct ata_host {
struct device *dev;
void __iomem * const *iomap;
unsigned int n_ports;
+ unsigned int n_tags; /* nr of NCQ tags */
void *private_data;
struct ata_port_operations *ops;
unsigned long flags;
--
1.9.1

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