Use helper function to access current->state.
Direct assignments are prone to races and therefore buggy.
Thanks to Peter Zijlstra for the exact definition of the problem.
Signed-off-by: Fabian Frederick <[email protected]>
---
drivers/block/swim.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/block/swim.c b/drivers/block/swim.c
index b5afd49..e9bb759 100644
--- a/drivers/block/swim.c
+++ b/drivers/block/swim.c
@@ -331,7 +331,7 @@ static inline void swim_motor(struct swim __iomem *base,
swim_select(base, RELAX);
if (swim_readbit(base, MOTOR_ON))
break;
- current->state = TASK_INTERRUPTIBLE;
+ set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(1);
}
} else if (action == OFF) {
@@ -350,7 +350,7 @@ static inline void swim_eject(struct swim __iomem *base)
swim_select(base, RELAX);
if (!swim_readbit(base, DISK_IN))
break;
- current->state = TASK_INTERRUPTIBLE;
+ set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(1);
}
swim_select(base, RELAX);
@@ -374,7 +374,7 @@ static inline int swim_step(struct swim __iomem *base)
for (wait = 0; wait < HZ; wait++) {
- current->state = TASK_INTERRUPTIBLE;
+ set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(1);
swim_select(base, RELAX);
--
2.1.0
Use helper function to access current->state.
Direct assignments are prone to races and therefore buggy.
Thanks to Peter Zijlstra for the exact definition of the problem.
Signed-off-by: Fabian Frederick <[email protected]>
---
drivers/isdn/hardware/mISDN/hfcpci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/isdn/hardware/mISDN/hfcpci.c b/drivers/isdn/hardware/mISDN/hfcpci.c
index 3c92780..ff48da6 100644
--- a/drivers/isdn/hardware/mISDN/hfcpci.c
+++ b/drivers/isdn/hardware/mISDN/hfcpci.c
@@ -1755,7 +1755,7 @@ init_card(struct hfc_pci *hc)
enable_hwirq(hc);
spin_unlock_irqrestore(&hc->lock, flags);
/* Timeout 80ms */
- current->state = TASK_UNINTERRUPTIBLE;
+ set_current_state(TASK_UNINTERRUPTIBLE);
schedule_timeout((80 * HZ) / 1000);
printk(KERN_INFO "HFC PCI: IRQ %d count %d\n",
hc->irq, hc->irqcnt);
--
2.1.0
Use helper functions to access current->state.
Direct assignments are prone to races and therefore buggy.
current->state = TASK_RUNNING can be replaced by __set_current_state()
Thanks to Peter Zijlstra for the exact definition of the problem.
Suggested-By: Peter Zijlstra <[email protected]>
Signed-off-by: Fabian Frederick <[email protected]>
---
drivers/macintosh/via-pmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/macintosh/via-pmu.c b/drivers/macintosh/via-pmu.c
index dee88e5..3c608d4 100644
--- a/drivers/macintosh/via-pmu.c
+++ b/drivers/macintosh/via-pmu.c
@@ -2109,7 +2109,7 @@ pmu_read(struct file *file, char __user *buf,
spin_lock_irqsave(&pp->lock, flags);
add_wait_queue(&pp->wait, &wait);
- current->state = TASK_INTERRUPTIBLE;
+ set_current_state(TASK_INTERRUPTIBLE);
for (;;) {
ret = -EAGAIN;
@@ -2138,7 +2138,7 @@ pmu_read(struct file *file, char __user *buf,
schedule();
spin_lock_irqsave(&pp->lock, flags);
}
- current->state = TASK_RUNNING;
+ __set_current_state(TASK_RUNNING);
remove_wait_queue(&pp->wait, &wait);
spin_unlock_irqrestore(&pp->lock, flags);
--
2.1.0
Use helper functions to access current->state.
Direct assignments are prone to races and therefore buggy.
current->state = TASK_RUNNING can be replaced by __set_current_state()
Thanks to Peter Zijlstra for the exact definition of the problem.
Suggested-By: Peter Zijlstra <[email protected]>
Signed-off-by: Fabian Frederick <[email protected]>
---
drivers/media/common/saa7146/saa7146_vbi.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/media/common/saa7146/saa7146_vbi.c b/drivers/media/common/saa7146/saa7146_vbi.c
index 1e71e37..2da9957 100644
--- a/drivers/media/common/saa7146/saa7146_vbi.c
+++ b/drivers/media/common/saa7146/saa7146_vbi.c
@@ -95,7 +95,7 @@ static int vbi_workaround(struct saa7146_dev *dev)
/* prepare to wait to be woken up by the irq-handler */
add_wait_queue(&vv->vbi_wq, &wait);
- current->state = TASK_INTERRUPTIBLE;
+ set_current_state(TASK_INTERRUPTIBLE);
/* start rps1 to enable workaround */
saa7146_write(dev, RPS_ADDR1, dev->d_rps1.dma_handle);
@@ -106,7 +106,7 @@ static int vbi_workaround(struct saa7146_dev *dev)
DEB_VBI("brs bug workaround %d/1\n", i);
remove_wait_queue(&vv->vbi_wq, &wait);
- current->state = TASK_RUNNING;
+ __set_current_state(TASK_RUNNING);
/* disable rps1 irqs */
SAA7146_IER_DISABLE(dev,MASK_28);
--
2.1.0
Use helper functions to access current->state.
Direct assignments are prone to races and therefore buggy.
Thanks to Peter Zijlstra for the exact definition of the problem.
Suggested-By: Peter Zijlstra <[email protected]>
Signed-off-by: Fabian Frederick <[email protected]>
---
drivers/net/usb/hso.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
index 9cdfb3f..778e915 100644
--- a/drivers/net/usb/hso.c
+++ b/drivers/net/usb/hso.c
@@ -1594,7 +1594,7 @@ hso_wait_modem_status(struct hso_serial *serial, unsigned long arg)
}
cprev = cnow;
}
- current->state = TASK_RUNNING;
+ __set_current_state(TASK_RUNNING);
remove_wait_queue(&tiocmget->waitq, &wait);
return ret;
--
2.1.0
Use helper functions to access current->state.
Direct assignments are prone to races and therefore buggy.
current->state = TASK_RUNNING is replaced by __set_current_state()
Thanks to Peter Zijlstra for the exact definition of the problem.
Suggested-By: Peter Zijlstra <[email protected]>
Signed-off-by: Fabian Frederick <[email protected]>
---
drivers/net/wan/cosa.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/drivers/net/wan/cosa.c b/drivers/net/wan/cosa.c
index 83c39e2..88d121d 100644
--- a/drivers/net/wan/cosa.c
+++ b/drivers/net/wan/cosa.c
@@ -806,21 +806,21 @@ static ssize_t cosa_read(struct file *file,
spin_lock_irqsave(&cosa->lock, flags);
add_wait_queue(&chan->rxwaitq, &wait);
while (!chan->rx_status) {
- current->state = TASK_INTERRUPTIBLE;
+ set_current_state(TASK_INTERRUPTIBLE);
spin_unlock_irqrestore(&cosa->lock, flags);
schedule();
spin_lock_irqsave(&cosa->lock, flags);
if (signal_pending(current) && chan->rx_status == 0) {
chan->rx_status = 1;
remove_wait_queue(&chan->rxwaitq, &wait);
- current->state = TASK_RUNNING;
+ __set_current_state(TASK_RUNNING);
spin_unlock_irqrestore(&cosa->lock, flags);
mutex_unlock(&chan->rlock);
return -ERESTARTSYS;
}
}
remove_wait_queue(&chan->rxwaitq, &wait);
- current->state = TASK_RUNNING;
+ __set_current_state(TASK_RUNNING);
kbuf = chan->rxdata;
count = chan->rxsize;
spin_unlock_irqrestore(&cosa->lock, flags);
@@ -890,14 +890,14 @@ static ssize_t cosa_write(struct file *file,
spin_lock_irqsave(&cosa->lock, flags);
add_wait_queue(&chan->txwaitq, &wait);
while (!chan->tx_status) {
- current->state = TASK_INTERRUPTIBLE;
+ set_current_state(TASK_INTERRUPTIBLE);
spin_unlock_irqrestore(&cosa->lock, flags);
schedule();
spin_lock_irqsave(&cosa->lock, flags);
if (signal_pending(current) && chan->tx_status == 0) {
chan->tx_status = 1;
remove_wait_queue(&chan->txwaitq, &wait);
- current->state = TASK_RUNNING;
+ __set_current_state(TASK_RUNNING);
chan->tx_status = 1;
spin_unlock_irqrestore(&cosa->lock, flags);
up(&chan->wsem);
@@ -905,7 +905,7 @@ static ssize_t cosa_write(struct file *file,
}
}
remove_wait_queue(&chan->txwaitq, &wait);
- current->state = TASK_RUNNING;
+ __set_current_state(TASK_RUNNING);
up(&chan->wsem);
spin_unlock_irqrestore(&cosa->lock, flags);
kfree(kbuf);
--
2.1.0
Use helper functions to access current->state.
Direct assignments are prone to races and therefore buggy.
Thanks to Peter Zijlstra for the exact definition of the problem.
Suggested-By: Peter Zijlstra <[email protected]>
Signed-off-by: Fabian Frederick <[email protected]>
---
drivers/tty/serial/serial_core.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 6a1055a..63d2947 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1118,8 +1118,7 @@ uart_wait_modem_status(struct uart_state *state, unsigned long arg)
cprev = cnow;
}
-
- current->state = TASK_RUNNING;
+ __set_current_state(TASK_RUNNING);
remove_wait_queue(&port->delta_msr_wait, &wait);
return ret;
--
2.1.0
Fabian Frederick wrote:
: Use helper functions to access current->state.
: Direct assignments are prone to races and therefore buggy.
:
: current->state = TASK_RUNNING is replaced by __set_current_state()
:
: Thanks to Peter Zijlstra for the exact definition of the problem.
OK, thanks. Although I wonder whether real users of COSA (an ISA-based
WAN card) do exist.
Acked-By: Jan "Yenya" Kasprzak <[email protected]>
-Y.
:
: Suggested-By: Peter Zijlstra <[email protected]>
: Signed-off-by: Fabian Frederick <[email protected]>
: ---
: drivers/net/wan/cosa.c | 12 ++++++------
: 1 file changed, 6 insertions(+), 6 deletions(-)
:
: diff --git a/drivers/net/wan/cosa.c b/drivers/net/wan/cosa.c
: index 83c39e2..88d121d 100644
: --- a/drivers/net/wan/cosa.c
: +++ b/drivers/net/wan/cosa.c
: @@ -806,21 +806,21 @@ static ssize_t cosa_read(struct file *file,
: spin_lock_irqsave(&cosa->lock, flags);
: add_wait_queue(&chan->rxwaitq, &wait);
: while (!chan->rx_status) {
: - current->state = TASK_INTERRUPTIBLE;
: + set_current_state(TASK_INTERRUPTIBLE);
: spin_unlock_irqrestore(&cosa->lock, flags);
: schedule();
: spin_lock_irqsave(&cosa->lock, flags);
: if (signal_pending(current) && chan->rx_status == 0) {
: chan->rx_status = 1;
: remove_wait_queue(&chan->rxwaitq, &wait);
: - current->state = TASK_RUNNING;
: + __set_current_state(TASK_RUNNING);
: spin_unlock_irqrestore(&cosa->lock, flags);
: mutex_unlock(&chan->rlock);
: return -ERESTARTSYS;
: }
: }
: remove_wait_queue(&chan->rxwaitq, &wait);
: - current->state = TASK_RUNNING;
: + __set_current_state(TASK_RUNNING);
: kbuf = chan->rxdata;
: count = chan->rxsize;
: spin_unlock_irqrestore(&cosa->lock, flags);
: @@ -890,14 +890,14 @@ static ssize_t cosa_write(struct file *file,
: spin_lock_irqsave(&cosa->lock, flags);
: add_wait_queue(&chan->txwaitq, &wait);
: while (!chan->tx_status) {
: - current->state = TASK_INTERRUPTIBLE;
: + set_current_state(TASK_INTERRUPTIBLE);
: spin_unlock_irqrestore(&cosa->lock, flags);
: schedule();
: spin_lock_irqsave(&cosa->lock, flags);
: if (signal_pending(current) && chan->tx_status == 0) {
: chan->tx_status = 1;
: remove_wait_queue(&chan->txwaitq, &wait);
: - current->state = TASK_RUNNING;
: + __set_current_state(TASK_RUNNING);
: chan->tx_status = 1;
: spin_unlock_irqrestore(&cosa->lock, flags);
: up(&chan->wsem);
: @@ -905,7 +905,7 @@ static ssize_t cosa_write(struct file *file,
: }
: }
: remove_wait_queue(&chan->txwaitq, &wait);
: - current->state = TASK_RUNNING;
: + __set_current_state(TASK_RUNNING);
: up(&chan->wsem);
: spin_unlock_irqrestore(&cosa->lock, flags);
: kfree(kbuf);
: --
: 2.1.0
--
| Jan "Yenya" Kasprzak <kas at {fi.muni.cz - work | yenya.net - private}> |
| New GPG 4096R/A45477D5 -- see http://www.fi.muni.cz/~kas/pgp-rollover.txt |
| http://www.fi.muni.cz/~kas/ Journal: http://www.fi.muni.cz/~kas/blog/ |
||| "New and improved" is only really improved if it also takes backwards |||
||| compatibility into account, rather than saying "now everybody must do |||
||| things the new and improved - and different - way" --Linus Torvalds |||
Hello.
On 02/20/2015 09:12 PM, Fabian Frederick wrote:
> Use helper functions to access current->state.
> Direct assignments are prone to races and therefore buggy.
> current->state = TASK_RUNNING is replaced by __set_current_state()
You sometimes use __set_current_state() and sometimes set_current_state().
> Thanks to Peter Zijlstra for the exact definition of the problem.
> Suggested-By: Peter Zijlstra <[email protected]>
> Signed-off-by: Fabian Frederick <[email protected]>
[...]
WBR, Sergei
> On 20 February 2015 at 19:34 Sergei Shtylyov
> <[email protected]> wrote:
>
>
> Hello.
>
> On 02/20/2015 09:12 PM, Fabian Frederick wrote:
>
> > Use helper functions to access current->state.
> > Direct assignments are prone to races and therefore buggy.
>
> > current->state = TASK_RUNNING is replaced by __set_current_state()
>
> You sometimes use __set_current_state() and sometimes set_current_state().
Hello Sergei,
Peter suggested to use __set_current_state() for TASK_RUNNING :
http://marc.info/?l=linux-kernel&m=142442259719216&w=2
Regards,
Fabian
>
> > Thanks to Peter Zijlstra for the exact definition of the problem.
>
> > Suggested-By: Peter Zijlstra <[email protected]>
> > Signed-off-by: Fabian Frederick <[email protected]>
>
> [...]
>
> WBR, Sergei
>
On Fri, Feb 20, 2015 at 09:34:28PM +0300, Sergei Shtylyov wrote:
> Hello.
>
> On 02/20/2015 09:12 PM, Fabian Frederick wrote:
>
> >Use helper functions to access current->state.
> >Direct assignments are prone to races and therefore buggy.
>
> >current->state = TASK_RUNNING is replaced by __set_current_state()
>
> You sometimes use __set_current_state() and sometimes set_current_state().
It depends on which state; setting yourself TASK_RUNNING is free of
wakeup races -- you're already running after all, so it can safely use
__set_current_state().
Setting a blocking state otoh needs set_current_state() which issues a
full memory barriers with the store (critically in this case,
effectively after the store) such that it orders the state store with a
subsequent load in the condition check if it really needs to go to
sleep.
In full:
current->state = TASK_UNINTERRUPTIBLE; wait = false;
smp_mb(); smp_wmb();
if (wait) p->state = TASK_RUNNING;
schedule();
Without that smp_mb(); the following order is possible:
if (wait)
wait = false;
smp_wmb();
p->state = TASK_RUNNING;
current->state = TASK_UNINTERRUPTIBLE;
schedule();
And we'll wait forever more..
On 02/20/2015 09:51 PM, Fabian Frederick wrote:
>>> Use helper functions to access current->state.
>>> Direct assignments are prone to races and therefore buggy.
>>> current->state = TASK_RUNNING is replaced by __set_current_state()
>> You sometimes use __set_current_state() and sometimes set_current_state().
> Hello Sergei,
> Peter suggested to use __set_current_state() for TASK_RUNNING :
> http://marc.info/?l=linux-kernel&m=142442259719216&w=2
I didn't even question your decisions, I (like Peter) just wanted a more
coherent change-log. Thanks to Peter for the explanations though. :-)
> Regards,
> Fabian
>>> Thanks to Peter Zijlstra for the exact definition of the problem.
>>> Suggested-By: Peter Zijlstra <[email protected]>
>>> Signed-off-by: Fabian Frederick <[email protected]>
>> [...]
WBR, Sergei
On Fri, 2015-02-20 at 19:58 +0100, Peter Zijlstra wrote:
> On Fri, Feb 20, 2015 at 09:34:28PM +0300, Sergei Shtylyov wrote:
> > Hello.
> >
> > On 02/20/2015 09:12 PM, Fabian Frederick wrote:
> >
> > >Use helper functions to access current->state.
> > >Direct assignments are prone to races and therefore buggy.
> >
> > >current->state = TASK_RUNNING is replaced by __set_current_state()
> >
> > You sometimes use __set_current_state() and sometimes set_current_state().
>
> It depends on which state; setting yourself TASK_RUNNING is free of
> wakeup races -- you're already running after all, so it can safely use
> __set_current_state().
Maybe this might be self documented in set_current_state(),
as we have about 120 calls to __set_current_state(TASK_RUNNING)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 41c60e5302d7..26133da6445e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -275,7 +275,11 @@ extern char ___assert_task_state[1 - 2*!!(
#define set_current_state(state_value) \
do { \
current->task_state_change = _THIS_IP_; \
- set_mb(current->state, (state_value)); \
+ if (__builtin_constant_p(state_value) && \
+ (state_value) == TASK_RUNNING) \
+ current->state = (state_value); \
+ else \
+ set_mb(current->state, (state_value)); \
} while (0)
#else
On Fri, 2015-02-20 at 11:31 -0800, Eric Dumazet wrote:
> On Fri, 2015-02-20 at 19:58 +0100, Peter Zijlstra wrote:
> > On Fri, Feb 20, 2015 at 09:34:28PM +0300, Sergei Shtylyov wrote:
> > > Hello.
> > >
> > > On 02/20/2015 09:12 PM, Fabian Frederick wrote:
> > >
> > > >Use helper functions to access current->state.
> > > >Direct assignments are prone to races and therefore buggy.
> > >
> > > >current->state = TASK_RUNNING is replaced by __set_current_state()
> > >
> > > You sometimes use __set_current_state() and sometimes set_current_state().
> >
> > It depends on which state; setting yourself TASK_RUNNING is free of
> > wakeup races -- you're already running after all, so it can safely use
> > __set_current_state().
>
> Maybe this might be self documented in set_current_state(),
> as we have about 120 calls to __set_current_state(TASK_RUNNING)
And about 138 calls to set_current_state(TASK_RUNNING)
On Fri, Feb 20, 2015 at 11:31:53AM -0800, Eric Dumazet wrote:
> On Fri, 2015-02-20 at 19:58 +0100, Peter Zijlstra wrote:
> Maybe this might be self documented in set_current_state(),
> as we have about 120 calls to __set_current_state(TASK_RUNNING)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 41c60e5302d7..26133da6445e 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -275,7 +275,11 @@ extern char ___assert_task_state[1 - 2*!!(
> #define set_current_state(state_value) \
> do { \
> current->task_state_change = _THIS_IP_; \
> - set_mb(current->state, (state_value)); \
> + if (__builtin_constant_p(state_value) && \
> + (state_value) == TASK_RUNNING) \
> + current->state = (state_value); \
> + else \
> + set_mb(current->state, (state_value)); \
> } while (0)
lkml.kernel.org/r/[email protected]
The problem is that there _might_ be someone relying on that barrier.
Its (very) unlikely, but you don't want to risk subtle borkage just
because. And I'm too lazy to go audit all of them :/
> On 20 February 2015 at 19:58 Peter Zijlstra <[email protected]> wrote:
>
>
> On Fri, Feb 20, 2015 at 09:34:28PM +0300, Sergei Shtylyov wrote:
> > Hello.
> >
> > On 02/20/2015 09:12 PM, Fabian Frederick wrote:
> >
> > >Use helper functions to access current->state.
> > >Direct assignments are prone to races and therefore buggy.
> >
> > >current->state = TASK_RUNNING is replaced by __set_current_state()
> >
> > You sometimes use __set_current_state() and sometimes
> >set_current_state().
>
> It depends on which state; setting yourself TASK_RUNNING is free of
> wakeup races -- you're already running after all, so it can safely use
> __set_current_state().
>
> Setting a blocking state otoh needs set_current_state() which issues a
> full memory barriers with the store (critically in this case,
> effectively after the store) such that it orders the state store with a
> subsequent load in the condition check if it really needs to go to
> sleep.
>
>
> In full:
>
> current->state = TASK_UNINTERRUPTIBLE; wait = false;
> smp_mb(); smp_wmb();
> if (wait) p->state = TASK_RUNNING;
> schedule();
>
> Without that smp_mb(); the following order is possible:
>
> if (wait)
> wait = false;
> smp_wmb();
> p->state = TASK_RUNNING;
> current->state = TASK_UNINTERRUPTIBLE;
> schedule();
>
> And we'll wait forever more..
Do I have to add more comments in changelogs or is it OK for you ?
Maybe something like:
"
current->state = TASK_RUNNING can safely be converted to __set_current_state()
as we're already in that state. Other assignments are converted to
set_current_state() (which uses set_mb()).
"
Regards,
Fabian
>
From: Fabian Frederick <[email protected]>
Date: Fri, 20 Feb 2015 19:12:52 +0100
> Use helper function to access current->state.
> Direct assignments are prone to races and therefore buggy.
>
> Thanks to Peter Zijlstra for the exact definition of the problem.
>
> Signed-off-by: Fabian Frederick <[email protected]>
Applied.
From: Fabian Frederick <[email protected]>
Date: Fri, 20 Feb 2015 19:12:55 +0100
> Use helper functions to access current->state.
> Direct assignments are prone to races and therefore buggy.
>
> Thanks to Peter Zijlstra for the exact definition of the problem.
>
> Suggested-By: Peter Zijlstra <[email protected]>
> Signed-off-by: Fabian Frederick <[email protected]>
Applied.
From: Fabian Frederick <[email protected]>
Date: Fri, 20 Feb 2015 19:12:56 +0100
> Use helper functions to access current->state.
> Direct assignments are prone to races and therefore buggy.
>
> current->state = TASK_RUNNING is replaced by __set_current_state()
>
> Thanks to Peter Zijlstra for the exact definition of the problem.
>
> Suggested-By: Peter Zijlstra <[email protected]>
> Signed-off-by: Fabian Frederick <[email protected]>
Applied.