Re: [PATCH] Bluetooth: btmtksdio: fix infinite loop in btmtksdio_txrx_work()

[Takashi Iwai <tiwai@suse.de>]

On Wed, 10 Jun 2026 08:52:31 +0200,
Sean Wang wrote:
> 
> Hi,
> 
> On Tue, Jun 9, 2026 at 7:19 AM Sergey Senozhatsky
> <senozhatsky@chromium.org> wrote:
> >
> > Every once in a while we see a hung btmtksdio_flush() task:
> >
> >  INFO: task kworker/u17:0:189 blocked for more than 122 seconds.
> >  __cancel_work_timer+0x3f4/0x460
> >  cancel_work_sync+0x1c/0x2c
> >  btmtksdio_flush+0x2c/0x40
> >  hci_dev_open_sync+0x10c4/0x2190
> >  [..]
> >
> > It all boils down to incorrect time_is_before_jiffies() usage in
> > btmtksdio_txrx_work().  The btmtksdio_txrx_work() loop is expected
> > to be terminated if running for longer than 5*HZ.  However the
> > timeout check is twisted:  time_is_before_jiffies(old_jiffies + 5*HZ)
> > evaluates to true when old_jiffies + 5*HZ is in the past i.e. when a
> > timeout has occurred.  Using OR with time_is_before_jiffies(txrx_timeout)
> > means that:
> > - before the 5-second timeout: the condition is `int_status || false`,
> >   so it loops as long as there are pending interrupts.
> > - after the 5-second timeout: the condition becomes `int_status || true`,
> >   which is always true.
> >
> > When the loop becomes infinite btmtksdio_txrx_work() loop never
> > terminates and never releases the SDIO host.
> >
> > Fix loop termination condition to actually enforce a 5*HZ timeout.
> >
> > Fixes: 26270bc189ea4 ("Bluetooth: btmtksdio: move interrupt service to work")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> > ---
> >  drivers/bluetooth/btmtksdio.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/bluetooth/btmtksdio.c b/drivers/bluetooth/btmtksdio.c
> > index 5b0fab7b89b5..c6f80c419e90 100644
> > --- a/drivers/bluetooth/btmtksdio.c
> > +++ b/drivers/bluetooth/btmtksdio.c
> > @@ -620,7 +620,7 @@ static void btmtksdio_txrx_work(struct work_struct *work)
> >                         if (btmtksdio_rx_packet(bdev, rx_size) < 0)
> >                                 bdev->hdev->stat.err_rx++;
> >                 }
> > -       } while (int_status || time_is_before_jiffies(txrx_timeout));
> > +       } while (int_status && time_is_after_jiffies(txrx_timeout));
> 
> yes, loop continues only while there is interrupt work and the timeout
> deadline is still in the future

I stumbled on this while backporting to distro kernels, and I wonder
whether this change is correct.

IIUC, this essentially makes the loop exiting right after the first
cycle; the patch changed from time_is_before_jiffies() to *_after_*(),
not only the logical OR to AND, and *_after_*() returns false, so the
whole condition becomes false, too.


thanks,

Takashi