MMC warning on Raspberry Pi 3 with linux-rpi 6.18.38-1

[MattM]

After running pacman -Syu today on a Raspberry Pi 3 (aarch64), the system became unstable after upgrading:
[2026-07-16T00:13:05+0200] [ALPM] upgraded raspberrypi-bootloader (20260707-1 -> 20260713-1)
[2026-07-16T00:13:51+0200] [ALPM] upgraded linux-rpi (6.18.37-2 -> 6.18.38-1)

After reboot, the new kernel showed mmc warnings during mount.
Relevant dmesg output:
[ 0.000000] Linux version 6.18.38-1-rpi (builduser@arch-nspawn-4136851) (aarch64-unknown-linux-gnu-gcc (GCC) 16.1.1 20260430, GNU ld (GNU Binutils) 2.46.0) #1 SMP PREEMPT Tue Jul 14 21:57:34 UTC 2026
...
[ 4.568525] ------------[ cut here ]------------
[ 4.568562] WARNING: CPU: 1 PID: 141 at drivers/mmc/core/queue.c:350 mmc_mq_queue_rq+0x2c0/0x300
[ 4.568595] Modules linked in: vc4 snd_soc_hdmi_codec drm_client_lib snd_soc_core snd_compress snd_pcm_dmaengine snd_pcm snd_timer snd drm_exec drm_display_helper drm_dma_helper drm_kms_helper drm drm_panel_orientation_quirks backlight cec
[ 4.568700] CPU: 1 UID: 0 PID: 141 Comm: mount Not tainted 6.18.38-1-rpi #1 PREEMPT
[ 4.568721] Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
...
[ 4.569585] ---[ end trace 0000000000000000 ]---
[ 4.848284] EXT4-fs (mmcblk0p2): mounted filesystem f8604c08-50c4-497d-a528-0c33378e4537 r/w with ordered data mode. Quota mode: none.

The root filesystem still mounted successfully, but I reverted to the previous kernel and bootloader:
sudo pacman -U /var/cache/pacman/pkg/raspberrypi-bootloader-20260707-1-any.pkg.tar.xz /var/cache/pacman/pkg/linux-rpi-6.18.37-2-aarch64.pkg.tar.xz

After reverting, the warning no longer appears.

This may be related to recent MMC changes in upstream linux-rpi:
[url]https://github.com/raspberrypi/linux/commit/e6c1e862b2b8150a419f4208e5bd7749662b16a1[/url]
mmc: restrict posted write counts for SD cards in CQ mode
...
[url]https://github.com/raspberrypi/linux/commit/66d46640d0a54ea21c4fffd0575e2b071333348a[/url]
mmc: don't reference requests after issuing them
Fixes: e6c1e86 ("mmc: restrict posted write counts for SD cards in CQ mode")
...

[graysky]

Please open an issue against the Raspberry Pi linux fork on GitHub if you suspect this is related to a change they're pushing into their code.

[sgk60]

Fix has been pushed to the raspberry pi fork.

[graysky]

I just pushed 6.18.38-3 with it