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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Fabio Aiuto <fabioaiuto83@gmail.com>
Cc:     outreachy-kernel@googlegroups.com,
        David Kershner <david.kershner@unisys.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org,
        Daniel Vetter <daniel@ffwll.ch>,
        Matthew Wilcox <willy@infradead.org>
Subject: Re: [Outreachy kernel] [PATCH v4] staging: unisys: visorhba: Convert module from IDR to XArray
Date:   Tue, 27 Apr 2021 16:27:16 +0200
Message-ID: <47635779.DuUUcalshs@linux.local>
In-Reply-To: <20210427140755.GC1399@agape.jhs>
References: <20210427132522.14547-1-fmdefrancesco@gmail.com> <20210427140755.GC1399@agape.jhs>
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On Tuesday, April 27, 2021 4:07:56 PM CEST Fabio Aiuto wrote:
> 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@gmail.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?
>
No reason at all. I unwittingly removed them while deleting idr_remove() 
calls.  I'll restore them.
> 
> >  /*
> > 
> > @@ -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?
>
Yes, I forgot to restore the previous format. Julia also pointed it out a few 
days ago.

Thanks,

Fabio
> 
> > @@ -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);
> 
> thank you,
> 
> fabio