Re: [PATCH] mmc: vub300: fix sleeping function called from invalid context

[Johan Hovold]

On Sun, Aug 09, 2026 at 02:09:50AM +0300, Ömer Mete Kaya wrote:
> syzbot reports:
> 
>   BUG: sleeping function called from invalid context at kernel/workqueue.c:4487
>   in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/1
>   ...
>    <IRQ>
>    __might_resched
>    __cancel_work_sync
>    mmc_free_host+0x19/0x30 [drivers/mmc/core/host.c:700]
>    call_timer_fn+0x192/0x5e0 [kernel/time/timer.c:1748]
>    run_timer_softirq
>    ...
> 
> vub300_inactivity_timer_expired() runs in softirq (timer) context.
> When the USB interface had already gone away (->interface == NULL,
> cleared by vub300_disconnect() or the probe() error path), the timer
> handler dropped the object's last kref via
> kref_put(&vub300->kref, vub300_delete). If that was the last
> reference, vub300_delete() ran from softirq context and called
> mmc_free_host(), which calls cancel_delayed_work_sync() - a sleeping
> function, illegal from softirq/timer context.
> 
> Root cause: inactivity_timer is armed in probe() and continuously
> re-armed via mod_timer(), but - unlike sg_transfer_timer, which is
> explicitly deleted after each use - it is never stopped when the
> device is torn down, so it can still fire after ->interface has
> been cleared.
> 
> Fix this by decoupling inactivity_timer from the object's kref
> entirely: drop the kref_get() taken on its behalf in probe(); make
> vub300_inactivity_timer_expired() a no-op when ->interface is NULL
> instead of dropping a reference; and in both vub300_disconnect() and
> the probe() err_stop_io path, call
> timer_delete_sync(&vub300->inactivity_timer) right after clearing
> ->interface and before the final kref_put(). Since ->interface is
> already NULL at that point, any concurrently running timer instance
> takes the no-op branch, so timer_delete_sync() is guaranteed to
> return with the timer stopped for good - removing any race with the
> final kref_put()/vub300_delete()/mmc_free_host(). Before this
> patch, a successful probe() left two references on the kref (one
> from kref_init(), one from the timer's kref_get()); after it, only
> the initial kref_init() reference remains, matching the single
> kref_put() in vub300_disconnect() and err_stop_io.
> 
> While auditing the driver for the same class of bug, also switch
> sg_transfer_timer's two timer_delete() call sites (in
> __command_read_data() and __command_write_data()) to
> timer_delete_sync(), since usb_sg_wait() returning does not
> guarantee a concurrently running vub300_sg_timed_out() has finished.
> __command_write_data() additionally only deleted the timer on the
> success path, leaking an armed timer on the cmd->error path; the
> (now synchronous) delete is moved before that check so it always
> runs.
> 
> Reported-by: syzbot+0e06aa1bdc6495bac24b@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=0e06aa1bdc6495bac24b
> Fixes: 88095e7b473a ("mmc: Add new VUB300 USB-to-SD/SDIO/MMC driver")
> Signed-off-by: Ömer Mete Kaya <omermetekaya0@xxxxxxxxx>

This is clearly LLM generated, so why didn't you add an Assisted-by tag
as required?

Johan