Re: [PATCH] mmc: vub300: fix sleeping function call from invalid context in vub300_inactivity_timer_expired

[Johan Hovold <johan@kernel.org>]

[ +CC: Geert ]

On Sun, Aug 16, 2026 at 05:38:09PM +0200, Jakov Novak wrote:
>  Currently, the function vub300_inactivity_timer_expired, which gets
>  called in a softirq context, calls a sleeping function in the following
>  call chain:
> 
>  vub300_inactivity_timer_expired -> kref_put -> vub300_delete ->
>  mmc_free_host -> cancel_delayed_work_sync -> __cancel_work_sync ->
>  might_sleep -> BUG
> 
>  Fix this by replacing kref_put(&vub300->kref, vub300_delete) with
>  vub300_queue_dead_work(vub300), which does the same thing, but in a
>  workqueue context.
> 
> Fixes: 88095e7b473a ("mmc: Add new VUB300 USB-to-SD/SDIO/MMC driver")

This isn't the commit that introduced the issue. The blocking call in
mmc_free_host() was added by commit 1036f69e2513 ("mmc: core: Cancel
delayed work before releasing host") in 2023. 

I didn't look at this in any detail, but having that call in
mmc_free_host() (e.g. rather than in mmc_remove_host()) looks wrong so
perhaps the fix really lies in MMC core.

> Reported-and-tested-by: syzbot+1ee4f3b9228e35f14677@syzkaller.appspotmail.com

Not sure if syzbot has started suggesting this tag, but this should
be two separate tags.

> Closes: https://syzkaller.appspot.com/bug?extid=1ee4f3b9228e35f14677
> Signed-off-by: Jakov Novak <jakovnovak30@gmail.com>
> ---
>  drivers/mmc/host/vub300.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/vub300.c b/drivers/mmc/host/vub300.c
> index 2dae474dcd06..df0096bc53db 100644
> --- a/drivers/mmc/host/vub300.c
> +++ b/drivers/mmc/host/vub300.c
> @@ -744,7 +744,7 @@ static void vub300_inactivity_timer_expired(struct timer_list *t)
>  	struct vub300_mmc_host *vub300 = timer_container_of(vub300, t,
>  							    inactivity_timer);
>  	if (!vub300->interface) {
> -		kref_put(&vub300->kref, vub300_delete);
> +		vub300_queue_dead_work(vub300);
>  	} else if (vub300->cmd) {
>  		mod_timer(&vub300->inactivity_timer, jiffies + HZ);
>  	} else {

Johan