Date:   Tue, 27 Apr 2021 16:07:56 +0200
From:   Fabio Aiuto <fabioaiuto83@...il.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     outreachy-kernel@...glegroups.com,
        David Kershner <david.kershner@...sys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel@...ll.ch>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [Outreachy kernel] [PATCH v4] staging: unisys: visorhba: Convert
 module from IDR to XArray

Hi Fabio,

On Tue, Apr 27, 2021 at 03:25:22PM +0200, Fabio M. De Francesco wrote:
> Converted visorhba from IDR to XArray. The abstract data type XArray is
> more memory-efficient, parallelisable and cache friendly. It takes
> advantage of RCU to perform lookups without locking.
> 
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
> 
> Changes from v3: Matthew Wilcox found that the XArray was not
> initialized: now it is. Changed types handles from u64 to u32 because
> they can't work as arguments of xa_alloc_irq() and u32 is enough large
> for storing XArray indexes.
> Changes from v2: Some residual errors from v1 were not fixed in v2. Now
> they have been removed.
> Changes from v1: After a first review by Matthew Wilcox, who found a
> series of errors and gave suggestions on how to fix them, I rewrote a
> larger part of the patch.
> 
>  drivers/staging/unisys/include/iochannel.h    |  4 +-
>  .../staging/unisys/visorhba/visorhba_main.c   | 89 ++++++-------------
>  2 files changed, 28 insertions(+), 65 deletions(-)
> 
> diff --git a/drivers/staging/unisys/include/iochannel.h b/drivers/staging/unisys/include/iochannel.h
> index 9ef812c0bc42..fac89eac148b 100644
> --- a/drivers/staging/unisys/include/iochannel.h
> +++ b/drivers/staging/unisys/include/iochannel.h
> @@ -474,8 +474,8 @@ struct uiscmdrsp_scsitaskmgmt {
>  	enum task_mgmt_types tasktype;
>  	struct uisscsi_dest vdest;
>  	u64 handle;
> -	u64 notify_handle;
> -	u64 notifyresult_handle;
> +	u32 notify_handle;
> +	u32 notifyresult_handle;
>  	char result;
>  
>  #define TASK_MGMT_FAILED 0
> diff --git a/drivers/staging/unisys/visorhba/visorhba_main.c b/drivers/staging/unisys/visorhba/visorhba_main.c
> index 4455d26f7c96..2b6cde254f17 100644
> --- a/drivers/staging/unisys/visorhba/visorhba_main.c
> +++ b/drivers/staging/unisys/visorhba/visorhba_main.c
> @@ -6,10 +6,10 @@
>  
>  #include <linux/debugfs.h>
>  #include <linux/kthread.h>
> -#include <linux/idr.h>
>  #include <linux/module.h>
>  #include <linux/seq_file.h>
>  #include <linux/visorbus.h>
> +#include <linux/xarray.h>
>  #include <scsi/scsi.h>
>  #include <scsi/scsi_host.h>
>  #include <scsi/scsi_cmnd.h>
> @@ -82,7 +82,7 @@ struct visorhba_devdata {
>  	 * allows us to pass int handles back-and-forth between us and
>  	 * iovm, instead of raw pointers
>  	 */
> -	struct idr idr;
> +	struct xarray xa;
>  
>  	struct dentry *debugfs_dir;
>  	struct dentry *debugfs_info;
> @@ -182,71 +182,40 @@ static struct uiscmdrsp *get_scsipending_cmdrsp(struct visorhba_devdata *ddata,
>  	return NULL;
>  }
>  
> -/*
> - * simple_idr_get - Associate a provided pointer with an int value
> - *		    1 <= value <= INT_MAX, and return this int value;
> - *		    the pointer value can be obtained later by passing
> - *		    this int value to idr_find()
> - * @idrtable: The data object maintaining the pointer<-->int mappings
> - * @p:	      The pointer value to be remembered
> - * @lock:     A spinlock used when exclusive access to idrtable is needed
> - *
> - * Return: The id number mapped to pointer 'p', 0 on failure
> - */
> -static unsigned int simple_idr_get(struct idr *idrtable, void *p,
> -				   spinlock_t *lock)
> -{
> -	int id;
> -	unsigned long flags;
> -
> -	idr_preload(GFP_KERNEL);
> -	spin_lock_irqsave(lock, flags);
> -	id = idr_alloc(idrtable, p, 1, INT_MAX, GFP_NOWAIT);
> -	spin_unlock_irqrestore(lock, flags);
> -	idr_preload_end();
> -	/* failure */
> -	if (id < 0)
> -		return 0;
> -	/* idr_alloc() guarantees > 0 */
> -	return (unsigned int)(id);
> -}
> -
>  /*
>   * setup_scsitaskmgmt_handles - Stash the necessary handles so that the
>   *				completion processing logic for a taskmgmt
>   *				cmd will be able to find who to wake up
>   *				and where to stash the result
> - * @idrtable: The data object maintaining the pointer<-->int mappings
> - * @lock:     A spinlock used when exclusive access to idrtable is needed
> + * @xa:       The data object maintaining the pointer<-->int mappings
>   * @cmdrsp:   Response from the IOVM
>   * @event:    The event handle to associate with an id
>   * @result:   The location to place the result of the event handle into
>   */
> -static void setup_scsitaskmgmt_handles(struct idr *idrtable, spinlock_t *lock,
> -				       struct uiscmdrsp *cmdrsp,
> +static void setup_scsitaskmgmt_handles(struct xarray *xa, struct uiscmdrsp *cmdrsp,
>  				       wait_queue_head_t *event, int *result)
>  {
> -	/* specify the event that has to be triggered when this */
> -	/* cmd is complete */
> -	cmdrsp->scsitaskmgmt.notify_handle =
> -		simple_idr_get(idrtable, event, lock);
> -	cmdrsp->scsitaskmgmt.notifyresult_handle =
> -		simple_idr_get(idrtable, result, lock);
> +	int ret;
> +	u32 *id;
> +
> +	/* specify the event that has to be triggered when this cmd is complete */
> +	id = &cmdrsp->scsitaskmgmt.notify_handle;
> +	ret = xa_alloc_irq(xa, id, event, XA_LIMIT(1, INT_MAX), GFP_KERNEL);
> +	id = &cmdrsp->scsitaskmgmt.notifyresult_handle;
> +	ret = xa_alloc_irq(xa, id, result, XA_LIMIT(1, INT_MAX), GFP_KERNEL);
>  }
>  
>  /*
>   * cleanup_scsitaskmgmt_handles - Forget handles created by
>   *				  setup_scsitaskmgmt_handles()
> - * @idrtable: The data object maintaining the pointer<-->int mappings
> + * @xa: The data object maintaining the pointer<-->int mappings
>   * @cmdrsp:   Response from the IOVM
>   */
> -static void cleanup_scsitaskmgmt_handles(struct idr *idrtable,
> +static void cleanup_scsitaskmgmt_handles(struct xarray *xa,
>  					 struct uiscmdrsp *cmdrsp)
>  {
> -	if (cmdrsp->scsitaskmgmt.notify_handle)
> -		idr_remove(idrtable, cmdrsp->scsitaskmgmt.notify_handle);
> -	if (cmdrsp->scsitaskmgmt.notifyresult_handle)
> -		idr_remove(idrtable, cmdrsp->scsitaskmgmt.notifyresult_handle);
> +	xa_erase(xa, cmdrsp->scsitaskmgmt.notify_handle);
> +	xa_erase(xa, cmdrsp->scsitaskmgmt.notifyresult_handle);
>  }

why were the conditions removed before each entry deletion?

>  
>  /*
> @@ -273,8 +242,7 @@ static int forward_taskmgmt_command(enum task_mgmt_types tasktype,
>  	if (devdata->serverdown || devdata->serverchangingstate)
>  		return FAILED;
>  
> -	scsicmd_id = add_scsipending_entry(devdata, CMD_SCSITASKMGMT_TYPE,
> -					   NULL);
> +	scsicmd_id = add_scsipending_entry(devdata, CMD_SCSITASKMGMT_TYPE, NULL);
>  	if (scsicmd_id < 0)
>  		return FAILED;
>  

this is a code format change, maybe this go in a separate patch?

> @@ -284,8 +252,7 @@ static int forward_taskmgmt_command(enum task_mgmt_types tasktype,
>  
>  	/* issue TASK_MGMT_ABORT_TASK */
>  	cmdrsp->cmdtype = CMD_SCSITASKMGMT_TYPE;
> -	setup_scsitaskmgmt_handles(&devdata->idr, &devdata->privlock, cmdrsp,
> -				   &notifyevent, &notifyresult);
> +	setup_scsitaskmgmt_handles(&devdata->xa, cmdrsp, &notifyevent, &notifyresult);
>  
>  	/* save destination */
>  	cmdrsp->scsitaskmgmt.tasktype = tasktype;
> @@ -311,14 +278,14 @@ static int forward_taskmgmt_command(enum task_mgmt_types tasktype,
>  	dev_dbg(&scsidev->sdev_gendev,
>  		"visorhba: taskmgmt type=%d success; result=0x%x\n",
>  		 tasktype, notifyresult);
> -	cleanup_scsitaskmgmt_handles(&devdata->idr, cmdrsp);
> +	cleanup_scsitaskmgmt_handles(&devdata->xa, cmdrsp);
>  	return SUCCESS;
>  
>  err_del_scsipending_ent:
>  	dev_dbg(&scsidev->sdev_gendev,
>  		"visorhba: taskmgmt type=%d not executed\n", tasktype);
>  	del_scsipending_ent(devdata, scsicmd_id);
> -	cleanup_scsitaskmgmt_handles(&devdata->idr, cmdrsp);
> +	cleanup_scsitaskmgmt_handles(&devdata->xa, cmdrsp);
>  	return FAILED;
>  }
>  
> @@ -654,13 +621,12 @@ DEFINE_SHOW_ATTRIBUTE(info_debugfs);
>   * Service Partition returned the result of the task management
>   * command. Wake up anyone waiting for it.
>   */
> -static void complete_taskmgmt_command(struct idr *idrtable,
> -				      struct uiscmdrsp *cmdrsp, int result)
> +static void complete_taskmgmt_command(struct xarray *xa, struct uiscmdrsp *cmdrsp, int result)
>  {
>  	wait_queue_head_t *wq =
> -		idr_find(idrtable, cmdrsp->scsitaskmgmt.notify_handle);
> +		xa_load(xa, cmdrsp->scsitaskmgmt.notify_handle);
>  	int *scsi_result_ptr =
> -		idr_find(idrtable, cmdrsp->scsitaskmgmt.notifyresult_handle);
> +		xa_load(xa, cmdrsp->scsitaskmgmt.notifyresult_handle);
>  	if (unlikely(!(wq && scsi_result_ptr))) {
>  		pr_err("visorhba: no completion context; cmd will time out\n");
>  		return;
> @@ -708,8 +674,7 @@ static void visorhba_serverdown_complete(struct visorhba_devdata *devdata)
>  			break;
>  		case CMD_SCSITASKMGMT_TYPE:
>  			cmdrsp = pendingdel->sent;
> -			complete_taskmgmt_command(&devdata->idr, cmdrsp,
> -						  TASK_MGMT_FAILED);
> +			complete_taskmgmt_command(&devdata->xa, cmdrsp, TASK_MGMT_FAILED);
>  			break;
>  		default:
>  			break;
> @@ -905,7 +870,7 @@ static void drain_queue(struct uiscmdrsp *cmdrsp,
>  			if (!del_scsipending_ent(devdata,
>  						 cmdrsp->scsitaskmgmt.handle))
>  				break;
> -			complete_taskmgmt_command(&devdata->idr, cmdrsp,
> +			complete_taskmgmt_command(&devdata->xa, cmdrsp,
>  						  cmdrsp->scsitaskmgmt.result);
>  		} else if (cmdrsp->cmdtype == CMD_NOTIFYGUEST_TYPE)
>  			dev_err_once(&devdata->dev->device,
> @@ -1053,7 +1018,7 @@ static int visorhba_probe(struct visor_device *dev)
>  	if (err)
>  		goto err_debugfs_info;
>  
> -	idr_init(&devdata->idr);
> +	xa_init(&devdata->xa);
>  
>  	devdata->cmdrsp = kmalloc(sizeof(*devdata->cmdrsp), GFP_ATOMIC);
>  	visorbus_enable_channel_interrupts(dev);
> @@ -1096,8 +1061,6 @@ static void visorhba_remove(struct visor_device *dev)
>  	scsi_remove_host(scsihost);
>  	scsi_host_put(scsihost);
>  
> -	idr_destroy(&devdata->idr);
> -
>  	dev_set_drvdata(&dev->device, NULL);
>  	debugfs_remove(devdata->debugfs_info);
>  	debugfs_remove_recursive(devdata->debugfs_dir);
> -- 
> 2.31.1
> 
> 

thank you,

fabio

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