Reproducible mmc_mq_queue_rq warning on linux-rpi 6.18.38 on Raspberry Pi 3 SD boot

[martham9]

Describe the bug

I’m seeing a reproducible mmc_mq_queue_rq warning on Arch Linux ARM linux-rpi 6.18.38-1 and 6.18.38-2 on a Raspberry Pi 3 Model B Rev 1.2 booting from SD card.

It does not prevent the root filesystem from mounting, but the warning disappears when I revert to 6.18.37-2 and reappears after upgrading again, so it looks like a regression.

I’m not certain whether the recent change in drivers/mmc/core/queue.c is the cause, but it seems like a possible candidate. Since this affects the SD boot path repeatedly, I wanted to report it in case it indicates a real issue.

Arch Linux ARM maintainer suggested opening an issue against the Raspberry Pi linux fork.

Package / commit info:
linux-rpi 6.18.37-2: Raspberry Pi linux commit 7136f2b7245f380ac9ae2b29fd556ca9567c6e1b
linux-rpi 6.18.38-1: Raspberry Pi linux commit d485ddf2eea99380b2724f6dc638d3d72e5294b3

There was a change in the MMC driver between those commits:
66d46640d0a54ea21c4fffd0575e2b071333348a
mmc: don't reference requests after issuing them
Fixes: e6c1e86 ("mmc: restrict posted write counts for SD cards in CQ mode")

Relevant dmesg excerpt from linux-rpi 6.18.38-1:

WARNING: CPU: 1 PID: 141 at drivers/mmc/core/queue.c:350 mmc_mq_queue_rq+0x2c0/0x300
CPU: 1 UID: 0 PID: 141 Comm: mount Not tainted 6.18.38-1-rpi #1 PREEMPT
Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
...
Call trace:
 mmc_mq_queue_rq+0x2c0/0x300
 blk_mq_dispatch_rq_list+0x160/0x6e0
 __blk_mq_sched_dispatch_requests+0x46c/0x598
 blk_mq_sched_dispatch_requests+0x34/0x88
 blk_mq_run_hw_queue+0xd0/0x2d8
 blk_mq_flush_plug_list+0x64/0x1a0
 __blk_flush_plug+0x100/0x168
 __submit_bio+0x1a0/0x230
 submit_bio_noacct_nocheck+0x24c/0x320
 submit_bio_noacct+0xd4/0x5b8
 submit_bio+0xa0/0x2b8
 submit_bh_wbc+0x12c/0x1b0
 submit_bh+0x20/0x40
 __ext4_read_bh+0x44/0xd0
 ext4_read_bh+0x58/0xd0
 __ext4_sb_bread_gfp.isra.0+0xac/0x150
 ext4_fill_super+0x194/0x2dc0
...
EXT4-fs (mmcblk0p2): mounted filesystem ... r/w with ordered data mode

Steps to reproduce the behaviour

Boot a Raspberry Pi 3 Model B from SD card with linux-rpi 6.18.38-1 or 6.18.38-2.
Observe the mmc_mq_queue_rq warning in dmesg during boot/mount.

Device (s)

Raspberry Pi 3 Mod. B

System

Kernel:
Linux ... 6.18.38-1-rpi #1 SMP PREEMPT Tue Jul 14 21:57:34 UTC 2026 aarch64 GNU/Linux
/etc/rpi-issue and vcgencmd not available on Arch Linux ARM

Logs

full dmesg output on linux-rpi 6.18.38-1-rpi

full dmesg output on linux-rpi 6.18.38-2-rpi

Additional context

No response

[pelwell]

I think this is the same issue reported by @mairacanal here: #7508

You will be able to install a trial fix in about 25 minutes by running sudo rpi-update pulls/7508. Be sure to read the caveats first.

[tomty89]

Also seeing this after updating linux-rpi to 6.18.38-2 on a Pi 4 running Arch Linux ARM.

[lhoward]

Also seeing since upgrading to 6.18.38 (we have a fork but it doesn't have any MMC related changes). Claude tells me eacf886 fixes this.

[martham9]

Seems fixed in Arch Linux ARM linux-rpi 6.18.38-3, which includes Raspberry Pi Linux commit eacf886641f744bb0ba4afdb26bccb2de86fb7e7.