diff mbox

[1/8] block/genhd.c: Add error handling

Message ID 1446812535-10567-1-git-send-email-vishnu.ps@samsung.com (mailing list archive)
State New, archived
Headers show

Commit Message

vishnu.ps Nov. 6, 2015, 12:22 p.m. UTC 
This patch adds error handling for blk_register_region(), register_disk(),
add_disk(), disk_alloc_events() & disk_add_events().
add_disk() & register_disk() functions  error handling is very much needed
as this is used mainly by many modules like mmc, zram, mtd, scsi etc.
But there is no error handling and it may cause stability issues also.

Verfied on X86 based ubuntu machine.

Signed-off-by: Vishnu Pratap Singh <vishnu.ps@samsung.com>
---
 block/genhd.c         | 89 +++++++++++++++++++++++++++++++++++----------------
 include/linux/genhd.h |  4 +--
 2 files changed, 64 insertions(+), 29 deletions(-)

Comments

Al Viro Nov. 10, 2015, 3:33 a.m. UTC | #1 
On Fri, Nov 06, 2015 at 05:52:08PM +0530, Vishnu Pratap Singh wrote:

Have you even tried to trigger the failure exits you've added?  The
more you've successfully set up, the _less_ your cleanup code ends
up undoing; that simply can't be right.

That aside, as soon as we'd done register_disk(), the damn thing is
available for open(), so bailing out is _really_ not something for
faint-hearted - it's essentially equivalent to removal of device under
somebody who'd opened it and might've started IO, etc.  Going there
simply because some sysfs shite didn't get created doesn't look sane
as far as I'm concerned...

Especially since these failure exits are not going to be tested on
a regular basis, so the amount of bitrot will be pretty high ;-/
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Jens Axboe Nov. 10, 2015, 3:40 a.m. UTC | #2 
On 11/09/2015 08:33 PM, Al Viro wrote:
> On Fri, Nov 06, 2015 at 05:52:08PM +0530, Vishnu Pratap Singh wrote:
>
> Have you even tried to trigger the failure exits you've added?  The
> more you've successfully set up, the _less_ your cleanup code ends
> up undoing; that simply can't be right.
>
> That aside, as soon as we'd done register_disk(), the damn thing is
> available for open(), so bailing out is _really_ not something for
> faint-hearted - it's essentially equivalent to removal of device under
> somebody who'd opened it and might've started IO, etc.  Going there
> simply because some sysfs shite didn't get created doesn't look sane
> as far as I'm concerned...
>
> Especially since these failure exits are not going to be tested on
> a regular basis, so the amount of bitrot will be pretty high ;-/

I'd greatly prefer it we just leave it alone. Much better to have a disk 
that does actually work and with some sysfs spew in the logs, than bail 
out for fairly vague reasons.

The road to hell is paved with good intentions. It's a noble thought to 
want to clean this up, but I think it does more harm than good.
Jeff Moyer Nov. 10, 2015, 2:11 p.m. UTC | #3 
Jens Axboe <axboe@kernel.dk> writes:

> On 11/09/2015 08:33 PM, Al Viro wrote:
>> On Fri, Nov 06, 2015 at 05:52:08PM +0530, Vishnu Pratap Singh wrote:
>>
>> Have you even tried to trigger the failure exits you've added?  The
>> more you've successfully set up, the _less_ your cleanup code ends
>> up undoing; that simply can't be right.
>>
>> That aside, as soon as we'd done register_disk(), the damn thing is
>> available for open(), so bailing out is _really_ not something for
>> faint-hearted - it's essentially equivalent to removal of device under
>> somebody who'd opened it and might've started IO, etc.  Going there
>> simply because some sysfs shite didn't get created doesn't look sane
>> as far as I'm concerned...
>>
>> Especially since these failure exits are not going to be tested on
>> a regular basis, so the amount of bitrot will be pretty high ;-/
>
> I'd greatly prefer it we just leave it alone. Much better to have a
> disk that does actually work and with some sysfs spew in the logs,
> than bail out for fairly vague reasons.
>
> The road to hell is paved with good intentions. It's a noble thought
> to want to clean this up, but I think it does more harm than good.

That's my fault, I asked Vishnu to repost.  I had also asked whether he
had seen this in the real world, and this was the response:

  Actually while working with zram I found that during zram
  initialization it uses the add_disk function and during that time i
  have seen sometimes under low mem condition when we enable swap (zram)
  there was kzalloc fail to allocate he memory, since there is no error
  handling it took good amount of time to debug.

Cheers,
Jeff
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diff mbox

Patch

diff --git a/block/genhd.c b/block/genhd.c
index 3213b66..a63ebd6 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -39,8 +39,8 @@  static struct device_type disk_type;
 
 static void disk_check_events(struct disk_events *ev,
 			      unsigned int *clearing_ptr);
-static void disk_alloc_events(struct gendisk *disk);
-static void disk_add_events(struct gendisk *disk);
+static int disk_alloc_events(struct gendisk *disk);
+static int disk_add_events(struct gendisk *disk);
 static void disk_del_events(struct gendisk *disk);
 static void disk_release_events(struct gendisk *disk);
 
@@ -473,11 +473,11 @@  static char *bdevt_str(dev_t devt, char *buf)
  * range must be nonzero
  * The hash chain is sorted on range, so that subranges can override.
  */
-void blk_register_region(dev_t devt, unsigned long range, struct module *module,
+int blk_register_region(dev_t devt, unsigned long range, struct module *module,
 			 struct kobject *(*probe)(dev_t, int *, void *),
 			 int (*lock)(dev_t, void *), void *data)
 {
-	kobj_map(bdev_map, devt, range, module, probe, lock, data);
+	return kobj_map(bdev_map, devt, range, module, probe, lock, data);
 }
 
 EXPORT_SYMBOL(blk_register_region);
@@ -505,7 +505,7 @@  static int exact_lock(dev_t devt, void *data)
 	return 0;
 }
 
-static void register_disk(struct gendisk *disk)
+static int register_disk(struct gendisk *disk)
 {
 	struct device *ddev = disk_to_dev(disk);
 	struct block_device *bdev;
@@ -520,14 +520,15 @@  static void register_disk(struct gendisk *disk)
 	/* delay uevents, until we scanned partition table */
 	dev_set_uevent_suppress(ddev, 1);
 
-	if (device_add(ddev))
-		return;
+	err = device_add(ddev);
+	if (err)
+		return err;
 	if (!sysfs_deprecated) {
 		err = sysfs_create_link(block_depr, &ddev->kobj,
 					kobject_name(&ddev->kobj));
 		if (err) {
 			device_del(ddev);
-			return;
+			return err;
 		}
 	}
 
@@ -569,6 +570,7 @@  exit:
 	while ((part = disk_part_iter_next(&piter)))
 		kobject_uevent(&part_to_dev(part)->kobj, KOBJ_ADD);
 	disk_part_iter_exit(&piter);
+	return err;
 }
 
 /**
@@ -577,10 +579,8 @@  exit:
  *
  * This function registers the partitioning information in @disk
  * with the kernel.
- *
- * FIXME: error handling
  */
-void add_disk(struct gendisk *disk)
+int add_disk(struct gendisk *disk)
 {
 	struct backing_dev_info *bdi;
 	dev_t devt;
@@ -598,7 +598,7 @@  void add_disk(struct gendisk *disk)
 	retval = blk_alloc_devt(&disk->part0, &devt);
 	if (retval) {
 		WARN_ON(1);
-		return;
+		return retval;
 	}
 	disk_to_dev(disk)->devt = devt;
 
@@ -608,17 +608,27 @@  void add_disk(struct gendisk *disk)
 	disk->major = MAJOR(devt);
 	disk->first_minor = MINOR(devt);
 
-	disk_alloc_events(disk);
-
+	retval = disk_alloc_events(disk);
+	if (retval)
+		goto err_blk_devt;
 	/* Register BDI before referencing it from bdev */
 	bdi = &disk->queue->backing_dev_info;
-	bdi_register_dev(bdi, disk_devt(disk));
+	retval = bdi_register_dev(bdi, disk_devt(disk));
+	if (retval)
+		goto err_alloc_event;
 
-	blk_register_region(disk_devt(disk), disk->minors, NULL,
+	retval = blk_register_region(disk_devt(disk), disk->minors, NULL,
 			    exact_match, exact_lock, disk);
-	register_disk(disk);
-	blk_register_queue(disk);
+	if (retval)
+		goto err_alloc_event;
+
+	retval = register_disk(disk);
+	if (retval)
+		goto err_reg_region;
 
+	retval = blk_register_queue(disk);
+	if (retval)
+		goto err_reg_disk;
 	/*
 	 * Take an extra ref on queue which will be put on disk_release()
 	 * so that it sticks around as long as @disk is there.
@@ -627,9 +637,28 @@  void add_disk(struct gendisk *disk)
 
 	retval = sysfs_create_link(&disk_to_dev(disk)->kobj, &bdi->dev->kobj,
 				   "bdi");
-	WARN_ON(retval);
+	if (retval)
+		goto err_blk_reg_queue;
+
+	retval = disk_add_events(disk);
+	if (retval)
+		goto err_sysfs;
 
-	disk_add_events(disk);
+	return 0;
+
+err_blk_devt:
+	blk_free_devt(devt);
+err_alloc_event:
+	disk_del_events(disk);
+err_reg_region:
+	blk_unregister_region(disk_devt(disk), disk->minors);
+err_reg_disk:
+	del_gendisk(disk);
+err_blk_reg_queue:
+	blk_unregister_queue(disk);
+err_sysfs:
+	sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
+	return retval;
 }
 EXPORT_SYMBOL(add_disk);
 
@@ -1782,17 +1811,17 @@  module_param_cb(events_dfl_poll_msecs, &disk_events_dfl_poll_msecs_param_ops,
 /*
  * disk_{alloc|add|del|release}_events - initialize and destroy disk_events.
  */
-static void disk_alloc_events(struct gendisk *disk)
+static int disk_alloc_events(struct gendisk *disk)
 {
 	struct disk_events *ev;
 
 	if (!disk->fops->check_events)
-		return;
+		return 0;
 
 	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 	if (!ev) {
 		pr_warn("%s: failed to initialize events\n", disk->disk_name);
-		return;
+		return -ENOMEM;
 	}
 
 	INIT_LIST_HEAD(&ev->node);
@@ -1804,17 +1833,22 @@  static void disk_alloc_events(struct gendisk *disk)
 	INIT_DELAYED_WORK(&ev->dwork, disk_events_workfn);
 
 	disk->ev = ev;
+	return 0;
 }
 
-static void disk_add_events(struct gendisk *disk)
+static int disk_add_events(struct gendisk *disk)
 {
+	int ret = 0;
+
 	if (!disk->ev)
-		return;
+		return ret;
 
-	/* FIXME: error handling */
-	if (sysfs_create_files(&disk_to_dev(disk)->kobj, disk_events_attrs) < 0)
+	ret = sysfs_create_files(&disk_to_dev(disk)->kobj, disk_events_attrs);
+	if (ret) {
 		pr_warn("%s: failed to create sysfs files for events\n",
 			disk->disk_name);
+		return ret;
+	}
 
 	mutex_lock(&disk_events_mutex);
 	list_add_tail(&disk->ev->node, &disk_events);
@@ -1825,6 +1859,7 @@  static void disk_add_events(struct gendisk *disk)
 	 * unblock kicks it into action.
 	 */
 	__disk_unblock_events(disk, true);
+	return ret;
 }
 
 static void disk_del_events(struct gendisk *disk)
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 2adbfa6..dae3160 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -417,7 +417,7 @@  static inline void free_part_info(struct hd_struct *part)
 extern void part_round_stats(int cpu, struct hd_struct *part);
 
 /* block/genhd.c */
-extern void add_disk(struct gendisk *disk);
+extern int add_disk(struct gendisk *disk);
 extern void del_gendisk(struct gendisk *gp);
 extern struct gendisk *get_gendisk(dev_t dev, int *partno);
 extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
@@ -620,7 +620,7 @@  extern struct gendisk *alloc_disk_node(int minors, int node_id);
 extern struct gendisk *alloc_disk(int minors);
 extern struct kobject *get_disk(struct gendisk *disk);
 extern void put_disk(struct gendisk *disk);
-extern void blk_register_region(dev_t devt, unsigned long range,
+extern int blk_register_region(dev_t devt, unsigned long range,
 			struct module *module,
 			struct kobject *(*probe)(dev_t, int *, void *),
 			int (*lock)(dev_t, void *),