Re: [PATCH] block: don't do revalidate zones on invalid devices

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2020/07/30 20:25, Johannes Thumshirn wrote:
> When we loose a device for whatever reason while (re)scanning zones, we
> trip over a NULL pointer in blk_revalidate_zone_cb, like in the following
> log:
> 
> sd 0:0:0:0: [sda] 3418095616 4096-byte logical blocks: (14.0 TB/12.7 TiB)
> sd 0:0:0:0: [sda] 52156 zones of 65536 logical blocks
> sd 0:0:0:0: [sda] Write Protect is off
> sd 0:0:0:0: [sda] Mode Sense: 37 00 00 08
> sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
> sd 0:0:0:0: [sda] REPORT ZONES start lba 1065287680 failed
> sd 0:0:0:0: [sda] REPORT ZONES: Result: hostbyte=0x00 driverbyte=0x08
> sd 0:0:0:0: [sda] Sense Key : 0xb [current]
> sd 0:0:0:0: [sda] ASC=0x0 ASCQ=0x6
> sda: failed to revalidate zones
> sd 0:0:0:0: [sda] 0 4096-byte logical blocks: (0 B/0 B)
> sda: detected capacity change from 14000519643136 to 0
> ==================================================================
> BUG: KASAN: null-ptr-deref in blk_revalidate_zone_cb+0x1b7/0x550
> Write of size 8 at addr 0000000000000010 by task kworker/u4:1/58
> 
> CPU: 1 PID: 58 Comm: kworker/u4:1 Not tainted 5.8.0-rc1 #692
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4-rebuilt.opensuse.org 04/01/2014
> Workqueue: events_unbound async_run_entry_fn
> Call Trace:
>  dump_stack+0x7d/0xb0
>  ? blk_revalidate_zone_cb+0x1b7/0x550
>  kasan_report.cold+0x5/0x37
>  ? blk_revalidate_zone_cb+0x1b7/0x550
>  check_memory_region+0x145/0x1a0
>  blk_revalidate_zone_cb+0x1b7/0x550
>  sd_zbc_parse_report+0x1f1/0x370
>  ? blk_req_zone_write_trylock+0x200/0x200
>  ? sectors_to_logical+0x60/0x60
>  ? blk_req_zone_write_trylock+0x200/0x200
>  ? blk_req_zone_write_trylock+0x200/0x200
>  sd_zbc_report_zones+0x3c4/0x5e0
>  ? sd_dif_config_host+0x500/0x500
>  blk_revalidate_disk_zones+0x231/0x44d
>  ? _raw_write_lock_irqsave+0xb0/0xb0
>  ? blk_queue_free_zone_bitmaps+0xd0/0xd0
>  sd_zbc_read_zones+0x8cf/0x11a0
>  sd_revalidate_disk+0x305c/0x64e0
>  ? __device_add_disk+0x776/0xf20
>  ? read_capacity_16.part.0+0x1080/0x1080
>  ? blk_alloc_devt+0x250/0x250
>  ? create_object.isra.0+0x595/0xa20
>  ? kasan_unpoison_shadow+0x33/0x40
>  sd_probe+0x8dc/0xcd2
>  really_probe+0x20e/0xaf0
>  __driver_attach_async_helper+0x249/0x2d0
>  async_run_entry_fn+0xbe/0x560
>  process_one_work+0x764/0x1290
>  ? _raw_read_unlock_irqrestore+0x30/0x30
>  worker_thread+0x598/0x12f0
>  ? __kthread_parkme+0xc6/0x1b0
>  ? schedule+0xed/0x2c0
>  ? process_one_work+0x1290/0x1290
>  kthread+0x36b/0x440
>  ? kthread_create_worker_on_cpu+0xa0/0xa0
>  ret_from_fork+0x22/0x30
> ==================================================================
> 
> When the device is already gone we end up with the following scenario:
> The device's capacity is 0 and thus the number of zones will be 0 as well. When
> allocating the bitmap for the conventional zones, we then trip over a NULL
> pointer.
> 
> So if we encounter a zoned block device with a 0 capacity, don't dare to
> revalidate the zones sizes.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> ---
> 
> Note: This is a hot-fix for 5.8, we're working on something to make a
> recoverable error recoverable.
> 
> 
>  block/blk-zoned.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
> index 23831fa8701d..480dfff69a00 100644
> --- a/block/blk-zoned.c
> +++ b/block/blk-zoned.c
> @@ -497,6 +497,9 @@ int blk_revalidate_disk_zones(struct gendisk *disk,
>  	if (WARN_ON_ONCE(!queue_is_mq(q)))
>  		return -EIO;
>  
> +	if (!get_capacity(disk))
> +		return -EIO;
> +
>  	/*
>  	 * Ensure that all memory allocations in this context are done as if
>  	 * GFP_NOIO was specified.
> 

I reworked sd_zbc_read_zones() and sd_zbc_revalidate_zones() to allow recovering
from simple temporary errors and avoid this problem. Will send the patch
tomorrow or so after some more testing.

But even with that patch applied, I think this patch makes the generic block
code more solid. So:

Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>


-- 
Damien Le Moal
Western Digital Research