Re: [PATCH libata/for-3.16-fixes] libata: introduce ata_host->n_tags to avoid oops on SAS controllers

[Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>]

Hi,

On Wednesday, July 23, 2014 10:46:31 AM Tejun Heo wrote:
> Hello, guys.
> 
> Sorry about the trouble.  Will soon push the below patch to Linus.
> 
> Thanks.
> 
> ------ 8< ------
> From 1a112d10f03e83fb3a2fdc4c9165865dec8a3ca6 Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@kernel.org>
> Date: Wed, 23 Jul 2014 09:05:27 -0400
> 
> 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

Hmmm, wasn't ATA_MAX_QUEUE used before not ATA_MAX_QUEUE - 1?

It seems that after your patch the loop in the ata_qc_new() will use
only 30 tags and not 31 ones?

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

> scsi_host->can_queue directly for SAS hosts anyway as they can go
> higher than the libata maximum.
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reported-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
> Reported-by: Jesse Brandeburg <jesse.brandeburg@gmail.com>
> Reported-by: Peter Hurley <peter@hurleysoftware.com>
> Reported-by: Peter Zijlstra <peterz@infradead.org>
> Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> Fixes: 1871ee134b73 ("libata: support the ata host which implements a queue depth less than 32")
> Cc: Kevin Hao <haokexin@gmail.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: stable@vger.kernel.org
> ---
>  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 d19c37a7..677c0c1 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))
> @@ -6094,6 +6093,7 @@ 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;
>  }
> @@ -6175,15 +6175,7 @@ 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 5ab4e3a..92abb49 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;