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Message-ID: <CANiDSCtk=_Qb4aC15otZiUrdysV2h82ihbA2eP2kWyQSovq=MQ@mail.gmail.com>
Date: Fri, 16 Aug 2024 10:20:47 +0200
From: Ricardo Ribalda <ribalda@...omium.org>
To: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org,
linux-kernel@...r.kernel.org, Hans Verkuil <hverkuil-cisco@...all.nl>
Subject: Re: [PATCH v2 2/2] media: drivers/media/dvb-core: Refactor
dvb_frontend_open locking
Hi Mauro
On Fri, 16 Aug 2024 at 10:17, Mauro Carvalho Chehab
<mchehab+huawei@...nel.org> wrote:
>
> Em Wed, 14 Aug 2024 14:10:23 +0000
> Ricardo Ribalda <ribalda@...omium.org> escreveu:
>
> > Split out the wait function, and introduce some new toys: guard and
> > lockdep.
> >
> > This fixes the following cocci warnings:
> > drivers/media/dvb-core/dvb_frontend.c:2897:1-7: preceding lock on line 2776
> > drivers/media/dvb-core/dvb_frontend.c:2897:1-7: preceding lock on line 2786
> > drivers/media/dvb-core/dvb_frontend.c:2897:1-7: preceding lock on line 2809
>
> Hi Ricardo,
Hi Mauro
>
> Every time someone tries to fix this lock, we end having regression reports,
> because of the diversity of devices, and the way they registers there.
>
> That's specially true for devices with multiple frontends and custom
> zigzag methods.
>
> On what devices have you tested this patch?
I do not have access to any device, it is just "compiled tested".
I think that the patch is mainly a refactor, it does not really change
how the lock is handled.
Regards!
>
> Regards,
> Mauro
>
> >
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> > drivers/media/dvb-core/dvb_frontend.c | 58 ++++++++++++++++++++++-------------
> > 1 file changed, 37 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
> > index e81b9996530e..7f5d0c297464 100644
> > --- a/drivers/media/dvb-core/dvb_frontend.c
> > +++ b/drivers/media/dvb-core/dvb_frontend.c
> > @@ -30,6 +30,7 @@
> > #include <linux/kthread.h>
> > #include <linux/ktime.h>
> > #include <linux/compat.h>
> > +#include <linux/lockdep.h>
> > #include <asm/processor.h>
> >
> > #include <media/dvb_frontend.h>
> > @@ -2826,6 +2827,34 @@ static int __dvb_frontend_open(struct inode *inode, struct file *file)
> > return ret;
> > }
> >
> > +static int wait_dvb_frontend(struct dvb_adapter *adapter,
> > + struct dvb_device *mfedev)
> > +{
> > + struct dvb_frontend *mfe = mfedev->priv;
> > + struct dvb_frontend_private *mfepriv = mfe->frontend_priv;
> > + int mferetry = (dvb_mfe_wait_time << 1);
> > + int ret = 0;
> > +
> > + lockdep_assert_held(&adapter->mfe_lock);
> > +
> > + if (mfedev->users == -1 && !mfepriv->thread)
> > + return 0;
> > +
> > + mutex_unlock(&adapter->mfe_lock);
> > +
> > + while (mferetry-- && (mfedev->users != -1 || mfepriv->thread)) {
> > + if (msleep_interruptible(500))
> > + if (signal_pending(current)) {
> > + ret = -EINTR;
> > + break;
> > + }
> > + }
> > +
> > + mutex_lock(&adapter->mfe_lock);
> > +
> > + return ret;
> > +}
> > +
> > static int dvb_frontend_open(struct inode *inode, struct file *file)
> > {
> > struct dvb_device *dvbdev = file->private_data;
> > @@ -2840,19 +2869,16 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
> > if (!adapter->mfe_shared)
> > return __dvb_frontend_open(inode, file);
> >
> > + guard(mutex)(&adapter->mfe_lock);
> > +
> > if (adapter->mfe_shared == 2) {
> > - mutex_lock(&adapter->mfe_lock);
> > if ((file->f_flags & O_ACCMODE) != O_RDONLY) {
> > if (adapter->mfe_dvbdev &&
> > - !adapter->mfe_dvbdev->writers) {
> > - mutex_unlock(&adapter->mfe_lock);
> > + !adapter->mfe_dvbdev->writers)
> > return -EBUSY;
> > - }
> > adapter->mfe_dvbdev = dvbdev;
> > }
> > } else {
> > - mutex_lock(&adapter->mfe_lock);
> > -
> > if (!adapter->mfe_dvbdev) {
> > adapter->mfe_dvbdev = dvbdev;
> > } else if (adapter->mfe_dvbdev != dvbdev) {
> > @@ -2862,34 +2888,24 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
> > *mfe = mfedev->priv;
> > struct dvb_frontend_private
> > *mfepriv = mfe->frontend_priv;
> > - int mferetry = (dvb_mfe_wait_time << 1);
> > -
> > - mutex_unlock(&adapter->mfe_lock);
> > - while (mferetry-- && (mfedev->users != -1 ||
> > - mfepriv->thread)) {
> > - if (msleep_interruptible(500)) {
> > - if (signal_pending(current))
> > - return -EINTR;
> > - }
> > - }
> >
> > - mutex_lock(&adapter->mfe_lock);
> > + ret = wait_dvb_frontend(adapter, mfedev);
> > + if (ret)
> > + return ret;
> > +
> > if (adapter->mfe_dvbdev != dvbdev) {
> > mfedev = adapter->mfe_dvbdev;
> > mfe = mfedev->priv;
> > mfepriv = mfe->frontend_priv;
> > if (mfedev->users != -1 ||
> > - mfepriv->thread) {
> > - mutex_unlock(&adapter->mfe_lock);
> > + mfepriv->thread)
> > return -EBUSY;
> > - }
> > adapter->mfe_dvbdev = dvbdev;
> > }
> > }
> > }
> >
> > ret = __dvb_frontend_open(inode, file);
> > - mutex_unlock(&adapter->mfe_lock);
> >
> > return ret;
> > }
> >
>
>
>
> Thanks,
> Mauro
--
Ricardo Ribalda
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