Re: [PATCH 09/30] mtd_blkdevs: use blk_mq_alloc_disk

Marek Szyprowski
2021-06-15T19:54:56Z

Hi,

On 02.06.2021 08:53, Christoph Hellwig wrote:
> Use the blk_mq_alloc_disk API to simplify the gendisk and request_queue
> allocation.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

This patch landed in linux-next as commit 6966bb921def ("mtd_blkdevs:
use blk_mq_alloc_disk"). It causes the following regression on my QEMU
arm64 setup:

Using buffer write method
Concatenating MTD devices:
(0): "0.flash"
(1): "0.flash"
into device "0.flash"
Unable to handle kernel NULL pointer dereference at virtual address
0000000000000068
Mem abort info:
ESR = 0x96000004
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
Data abort info:
ISV = 0, ISS = 0x00000004
CM = 0, WnR = 0
[0000000000000068] user address but active_mm is swapper
Internal error: Oops: 96000004 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc3+ #10492
Hardware name: linux,dummy-virt (DT)
pstate: 00000005 (nzcv daif -PAN -UAO -TCO BTYPE=--)
pc : blk_finish_plug+0x5c/0x268
lr : blk_queue_write_cache+0x28/0x70
...
Call trace:
blk_finish_plug+0x5c/0x268
add_mtd_blktrans_dev+0x270/0x420
mtdblock_add_mtd+0x68/0x98
blktrans_notify_add+0x44/0x70
add_mtd_device+0x41c/0x490
mtd_device_parse_register+0xf4/0x1c8
physmap_flash_probe+0x44c/0x780
platform_probe+0x90/0xd8
really_probe+0x108/0x3c0
driver_probe_device+0x60/0xc0
device_driver_attach+0x6c/0x78
__driver_attach+0xc0/0x100
bus_for_each_dev+0x68/0xc8
driver_attach+0x20/0x28
bus_add_driver+0x168/0x1f8
driver_register+0x60/0x110
__platform_driver_register+0x24/0x30
physmap_init+0x18/0x20
do_one_initcall+0x84/0x450
kernel_init_freeable+0x2dc/0x334
kernel_init+0x10/0x110
ret_from_fork+0x10/0x18
Code: 88027c01 35ffffa2 17fff079 f9800031 (c85f7c22)
---[ end trace b774518e0766cc92 ]---
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
SMP: stopping secondary CPUs
Kernel Offset: 0x594d1fa00000 from 0xffff800010000000
PHYS_OFFSET: 0xffffea7300000000
CPU features: 0x11000671,00000846
Memory Limit: none
---[ end Kernel panic - not syncing: Attempted to kill init!
exitcode=0x0000000b ]---

> ---
> drivers/mtd/mtd_blkdevs.c | 48 ++++++++++++++++++---------------------
> 1 file changed, 22 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> index fb8e12d590a1..5dc4c966ea73 100644
> --- a/drivers/mtd/mtd_blkdevs.c
> +++ b/drivers/mtd/mtd_blkdevs.c
> @@ -30,11 +30,9 @@ static void blktrans_dev_release(struct kref *kref)
> struct mtd_blktrans_dev *dev =
> container_of(kref, struct mtd_blktrans_dev, ref);
>
> - dev->disk->private_data = NULL;
> - blk_cleanup_queue(dev->rq);
> + blk_cleanup_disk(dev->disk);
> blk_mq_free_tag_set(dev->tag_set);
> kfree(dev->tag_set);
> - put_disk(dev->disk);
> list_del(&dev->list);
> kfree(dev);
> }
> @@ -354,7 +352,7 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
> if (new->devnum > (MINORMASK >> tr->part_bits) ||
> (tr->part_bits && new->devnum >= 27 * 26)) {
> mutex_unlock(&blktrans_ref_mutex);
> - goto error1;
> + return ret;
> }
>
> list_add_tail(&new->list, &tr->devs);
> @@ -366,17 +364,28 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
> if (!tr->writesect)
> new->readonly = 1;
>
> - /* Create gendisk */
> ret = -ENOMEM;
> - gd = alloc_disk(1 << tr->part_bits);
> + new->tag_set = kzalloc(sizeof(*new->tag_set), GFP_KERNEL);
> + if (!new->tag_set)
> + goto out_list_del;
>
> - if (!gd)
> - goto error2;
> + ret = blk_mq_alloc_sq_tag_set(new->tag_set, &mtd_mq_ops, 2,
> + BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_BLOCKING);
> + if (ret)
> + goto out_kfree_tag_set;
> +
> + /* Create gendisk */
> + gd = blk_mq_alloc_disk(new->tag_set, new);
> + if (IS_ERR(gd)) {
> + ret = PTR_ERR(gd);
> + goto out_free_tag_set;
> + }
>
> new->disk = gd;
> gd->private_data = new;
> gd->major = tr->major;
> gd->first_minor = (new->devnum) << tr->part_bits;
> + gd->minors = 1 << tr->part_bits;
> gd->fops = &mtd_block_ops;
>
> if (tr->part_bits)
> @@ -398,22 +407,9 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
> spin_lock_init(&new->queue_lock);
> INIT_LIST_HEAD(&new->rq_list);
>
> - new->tag_set = kzalloc(sizeof(*new->tag_set), GFP_KERNEL);
> - if (!new->tag_set)
> - goto error3;
> -
> - new->rq = blk_mq_init_sq_queue(new->tag_set, &mtd_mq_ops, 2,
> - BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_BLOCKING);
> - if (IS_ERR(new->rq)) {
> - ret = PTR_ERR(new->rq);
> - new->rq = NULL;
> - goto error4;
> - }
> -
> if (tr->flush)
> blk_queue_write_cache(new->rq, true, false);
>
> - new->rq->queuedata = new;
> blk_queue_logical_block_size(new->rq, tr->blksize);
>
> blk_queue_flag_set(QUEUE_FLAG_NONROT, new->rq);
> @@ -437,13 +433,13 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
> WARN_ON(ret);
> }
> return 0;
> -error4:
> +
> +out_free_tag_set:
> + blk_mq_free_tag_set(new->tag_set);
> +out_kfree_tag_set:
> kfree(new->tag_set);
> -error3:
> - put_disk(new->disk);
> -error2:
> +out_list_del:
> list_del(&new->list);
> -error1:
> return ret;
> }
>

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland