Re: [PATCH] mmc: vub300: never tear the host down from the inactivity timer

[Johan Hovold <johan@kernel.org>]

On Tue, Sep 08, 2026 at 10:20:50PM +0530, Yogesh Gaur wrote:
> vub300_probe() takes a second kref reference on behalf of the inactivity
> timer and arms it:
> 
> 	kref_init(&vub300->kref);
> 	...
> 	kref_get(&vub300->kref);
> 	timer_setup(&vub300->inactivity_timer,
> 		    vub300_inactivity_timer_expired, 0);
> 	vub300->inactivity_timer.expires = jiffies + HZ;
> 	add_timer(&vub300->inactivity_timer);
> 
> and expects the timer to release that reference from its own expiry
> function, once it observes that vub300->interface has been cleared:
> 
> 	if (!vub300->interface) {
> 		kref_put(&vub300->kref, vub300_delete);
> 	} else if (vub300->cmd) {
> 
> That is wrong in both directions, because the expiry function runs in
> softirq context.
> 
> If the timer happens to hold the last reference, the kref_put() runs
> vub300_delete() -> mmc_free_host() -> cancel_delayed_work_sync(), which
> sleeps. The ->probe() error path arranges exactly that: it clears
> ->interface and drops only its own reference, leaving the timer armed
> and owning the last one.
> 
> 	BUG: sleeping function called from invalid context at kernel/workqueue.c:4487
> 	in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 191, name: kworker/0:2
> 	Call Trace:
> 	 <IRQ>
> 	 __might_resched.cold+0x1ec/0x232 kernel/sched/core.c:9197
> 	 __cancel_work_sync kernel/workqueue.c:4487 [inline]
> 	 cancel_delayed_work_sync+0xb8/0xf0 kernel/workqueue.c:4568
> 	 mmc_free_host+0x19/0x30 drivers/mmc/core/host.c:700
> 	 vub300_delete drivers/mmc/host/vub300.c:379 [inline]
> 	 kref_put include/linux/kref.h:65 [inline]
> 	 vub300_inactivity_timer_expired drivers/mmc/host/vub300.c:747
> 	 call_timer_fn+0x11f/0x610 kernel/time/timer.c:1745
> 	 </IRQ>

> Fixes: 88095e7b473a ("mmc: Add new VUB300 USB-to-SD/SDIO/MMC driver")
> Reported-by: syzbot+f4a0159ce6802a0a4774@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=f4a0159ce6802a0a4774
> Reported-by: syzbot+1ee4f3b9228e35f14677@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=1ee4f3b9228e35f14677
> Signed-off-by: Yogesh Gaur <yogeshgaur.83@gmail.com>

You forgot to add an Assisted-by tag.

Several people have already proposed (LLM generated) fixes for this.
Please search the lists.

Johan