[Outreachy kernel] [PATCH v5] staging: unisys: visorhba: Convert module from IDR to XArray

From: Fabio M. De Francesco
Date: Tue Apr 27 2021 - 11:07:37 EST

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 v4: Fixed some issues detected by Matthew Wilcox and Fabio
Aiuto.
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.

.../staging/unisys/visorhba/visorhba_main.c | 84 ++++++-------------
1 file changed, 27 insertions(+), 57 deletions(-)

diff --git a/drivers/staging/unisys/visorhba/visorhba_main.c b/drivers/staging/unisys/visorhba/visorhba_main.c
index 4455d26f7c96..365666cedcd9 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 +182,44 @@ 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 */
+ ret = xa_alloc_irq(xa, &id, event, XA_LIMIT(1, INT_MAX), GFP_KERNEL);
+ if (ret == 0)
+ cmdrsp->scsitaskmgmt.notify_handle = id;
+ ret = xa_alloc_irq(xa, &id, result, XA_LIMIT(1, INT_MAX), GFP_KERNEL);
+ if (ret == 0)
+ cmdrsp->scsitaskmgmt.notifyresult_handle = id;
}

/*
* 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);
+ xa_erase(xa, cmdrsp->scsitaskmgmt.notify_handle);
if (cmdrsp->scsitaskmgmt.notifyresult_handle)
- idr_remove(idrtable, cmdrsp->scsitaskmgmt.notifyresult_handle);
+ xa_erase(xa, cmdrsp->scsitaskmgmt.notifyresult_handle);
}

/*
@@ -284,8 +257,7 @@ 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 +283,14 @@ 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 +626,13 @@ 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,
+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;
@@ -708,7 +680,7 @@ static void visorhba_serverdown_complete(struct visorhba_devdata *devdata)
break;
case CMD_SCSITASKMGMT_TYPE:
cmdrsp = pendingdel->sent;
- complete_taskmgmt_command(&devdata->idr, cmdrsp,
+ complete_taskmgmt_command(&devdata->xa, cmdrsp,
TASK_MGMT_FAILED);
break;
default:
@@ -905,7 +877,7 @@ 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 +1025,7 @@ 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 +1068,6 @@ 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