Re: [PATCH] NFC: nxp-nci: fix deadlock during firmware update

[Michael Walle]

Am 2022-07-13 08:57, schrieb Krzysztof Kozlowski:
> On 12/07/2022 17:25, Michael Walle wrote:
> > During firmware update, both nxp_nci_i2c_irq_thread_fn() and
> > nxp_nci_fw_work() will hold the info_lock mutex and one will wait
> > for the other via a completion:
> >
> > nxp_nci_fw_work()
> >   mutex_lock(info_lock)
> >   nxp_nci_fw_send()
> >     wait_for_completion(cmd_completion)
> >   mutex_unlock(info_lock)
> >
> > nxp_nci_i2c_irq_thread_fn()
> >   mutex_lock(info_lock)
> >     nxp_nci_fw_recv_frame()
> >       complete(cmd_completion)
> >   mutex_unlock(info_lock)
> >
> > This will result in a -ETIMEDOUT error during firmware update (note
> > that the wait_for_completion() above is a variant with a timeout).
> >
> > Drop the lock in nxp_nci_fw_work() and instead take it after the
> > work is done in nxp_nci_fw_work_complete() when the NFC controller 
> > mode
> > is switched and the info structure is updated.
> >
> > Fixes: dece45855a8b ("NFC: nxp-nci: Add support for NXP NCI chips")
> > Signed-off-by: Michael Walle <michael@xxxxxxxx>
> > ---
> >  drivers/nfc/nxp-nci/firmware.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/nfc/nxp-nci/firmware.c 
> > b/drivers/nfc/nxp-nci/firmware.c
> > index 119bf305c642..6a4d4aa7239f 100644
> > --- a/drivers/nfc/nxp-nci/firmware.c
> > +++ b/drivers/nfc/nxp-nci/firmware.c
> > @@ -54,6 +54,7 @@ void nxp_nci_fw_work_complete(struct nxp_nci_info 
> > *info, int result)
> >  	struct nxp_nci_fw_info *fw_info = &info->fw_info;
> >  	int r;
> >
> > +	mutex_lock(&info->info_lock);
> >  	if (info->phy_ops->set_mode) {
> >  		r = info->phy_ops->set_mode(info->phy_id, NXP_NCI_MODE_COLD);
> >  		if (r < 0 && result == 0)
> > @@ -66,6 +67,7 @@ void nxp_nci_fw_work_complete(struct nxp_nci_info 
> > *info, int result)
> >  		release_firmware(fw_info->fw);
> >  		fw_info->fw = NULL;
> >  	}
> > +	mutex_unlock(&info->info_lock);
> >
> >  	nfc_fw_download_done(info->ndev->nfc_dev, fw_info->name, (u32) 
> > -result);
> >  }
> > @@ -172,8 +174,6 @@ void nxp_nci_fw_work(struct work_struct *work)
> >  	fw_info = container_of(work, struct nxp_nci_fw_info, work);
> >  	info = container_of(fw_info, struct nxp_nci_info, fw_info);
> >
> > -	mutex_lock(&info->info_lock);
> > -
>
> I am not sure this is correct. info_lock should protect members of info
> thus also info->fw_info. By removing the mutex the protection is gone.
>
> Unless you are sure that fw_info cannot be modified concurrently?

Mh, you are right. fw_info could be modified by the irq thread and
in the worker thread (and the nfc core doesn't protect against
multiple fw_download() calls)

-michael