Re: [Outreachy kernel] [PATCH v4] staging: unisys: visorhba: Convert module from IDR to XArray

From: Fabio M. De Francesco
Date: Tue Apr 27 2021 - 10:27:26 EST

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@xxxxxxxxx>
> > ---
> >
> > 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