On Mon, Jun 15, 2026 at 09:20:23AM -0600, Keith Busch wrote:
> On Sun, Jun 14, 2026 at 05:57:48PM +0000, Dr. David Alan Gilbert wrote:
> > Jun 14 18:08:32 dalek kernel: device-mapper: raid1: Mirror read failed from
> > 252:24. Trying alternative device.
> > Jun 14 18:08:32 dalek kernel: ------------[ cut here ]------------
> > Jun 14 18:08:32 dalek dmeventd[1010]: Primary mirror device 252:24 read
> > failed.
> > Jun 14 18:08:32 dalek kernel: WARNING: block/bio.c:1044 at
> > bio_add_page+0x18b/0x250, CPU#15: kworker/15:1/369
> > Jun 14 18:08:32 dalek dmeventd[1010]: main-lvol0 is now in-sync.
> > Jun 14 18:08:32 dalek kernel: Modules linked in: nft_masq nft_reject_ipv4
> > act_csum cls_u32 sch_htb nf_nat_tftp nf_conntrack_tftp bridge stp llc
> > rfkill nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet
> > nf_reject_ipv4 nf_reje>
> > Jun 14 18:08:32 dalek kernel: drm_panel_backlight_quirks gpu_sched
> > drm_suballoc_helper video nvme drm_display_helper nvme_core cec
> > nvme_keyring sp5100_tco nvme_auth wmi serio_raw fuse scsi_dh_alua i2c_dev
> > scsi_dh_rdac scsi_dh_emc
> > Jun 14 18:08:32 dalek kernel: CPU: 15 UID: 0 PID: 369 Comm: kworker/15:1
> > Not tainted 7.1.0-rc7+ #786 PREEMPT(lazy)
> > Jun 14 18:08:32 dalek kernel: Hardware name: To Be Filled By O.E.M. To Be
> > Filled By O.E.M./X570 Pro4, BIOS P3.10 07/13/2020
> > Jun 14 18:08:32 dalek kernel: Workqueue: kmirrord do_mirror
> > Jun 14 18:08:32 dalek kernel: RIP: 0010:bio_add_page+0x18b/0x250
> > Jun 14 18:08:32 dalek kernel: Code: 24 10 4c 8b 04 24 84 c0 0f 85 c9 00 00
> > 00 41 0f b7 40 78 48 8b 74 24 08 8b 4c 24 14 e9 b4 fe ff ff 0f 0b 31 c0 e9
> > 55 d1 af 00 <0f> 0b eb f5 48 8b 7f 08 83 7f 60 05 0f 85 00 ff ff ff 49 8b
> > 3b 4c
> > Jun 14 18:08:32 dalek kernel: RSP: 0018:ffffd1fb8176fc10 EFLAGS: 00010246
> > Jun 14 18:08:32 dalek kernel: RAX: 0000000000000000 RBX: ffffd1fb8176fd18
> > RCX: 0000000000000000
> > Jun 14 18:08:32 dalek kernel: RDX: 0000000000000000 RSI: 0000000000000000
> > RDI: ffff8d1a8eb28b00
> > Jun 14 18:08:32 dalek kernel: RBP: 0000000000000000 R08: ffffd1fb8176fc38
> > R09: ffffd1fb8176fc40
> > Jun 14 18:08:32 dalek kernel: R10: ffffd1fb8176fc34 R11: 0000000000000000
> > R12: 0000000000000000
> > Jun 14 18:08:32 dalek kernel: R13: ffffd1fb8176fd90 R14: 0000000000000001
> > R15: ffff8d1a8eb28b00
> > Jun 14 18:08:32 dalek kernel: FS: 0000000000000000(0000)
> > GS:ffff8d29d161f000(0000) knlGS:0000000000000000
> > Jun 14 18:08:32 dalek kernel: CS: 0010 DS: 0000 ES: 0000 CR0:
> > 0000000080050033
> > Jun 14 18:08:32 dalek kernel: CR2: 00007f0ddcd7b9d0 CR3: 000000023dcbf000
> > CR4: 0000000000350ef0
> > Jun 14 18:08:32 dalek kernel: Call Trace:
> > Jun 14 18:08:32 dalek kernel: <TASK>
> > Jun 14 18:08:32 dalek kernel: do_region+0x227/0x2a0
>
> I think the problem is that do_region is tracking the "remaining" in
> sector granularity, but devices can have dma alignment such that it's
> valid to have sub-sector vectors. Rounding the length appended
> to_sectors() creates a 0 length subtraction, so the loop thinks no
> progress is made and loops forever. If we track it in bytes instead of
> sectors, then that should fix this observation.
I recreated your observation and this patch below appears to fix the
stuck behavior.
---
diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 1db565b376200..d72b9331c2fd1 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -362,19 +362,26 @@ static void do_region(const blk_opf_t opf, unsigned int
region,
bio->bi_iter.bi_size = num_sectors << SECTOR_SHIFT;
remaining -= num_sectors;
} else {
- while (remaining) {
+ unsigned long byte_remaining = to_bytes(remaining);
+
+ while (byte_remaining) {
/*
* Try and add as many pages as possible.
*/
dp->get_page(dp, &page, &len, &offset);
- len = min(len, to_bytes(remaining));
+ len = min(len, byte_remaining);
if (!bio_add_page(bio, page, len, offset))
break;
offset = 0;
- remaining -= to_sector(len);
+ byte_remaining -= len;
dp->next_page(dp);
}
+ remaining = to_sector(byte_remaining);
}
atomic_inc(&io->count);
--
