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Groups > linux.kernel > #1514671 > unrolled thread

[PATCH] Fix: disable sys_membarrier when nohz_full is enabled

Started byMathieu Desnoyers <mathieu.desnoyers@efficios.com>
First post2016-11-03 17:30 +0100
Last post2016-11-07 20:30 +0100
Articles 7 — 2 participants

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Contents

  [PATCH] Fix: disable sys_membarrier when nohz_full is enabled Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-11-03 17:30 +0100
    Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-03 18:50 +0100
      Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-11-07 18:10 +0100
        Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-11-07 19:20 +0100
          Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-08 07:40 +0100
            Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-11-08 12:20 +0100
        Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-11-07 20:30 +0100

#1514671 — [PATCH] Fix: disable sys_membarrier when nohz_full is enabled

FromMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date2016-11-03 17:30 +0100
Subject[PATCH] Fix: disable sys_membarrier when nohz_full is enabled
Message-ID<szt3P-6jb-7@gated-at.bofh.it>
Userspace applications should be allowed to expect the membarrier system
call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
nohz_full CPUs, but synchronize_sched() does not take those into
account.

Given that we do not want unrelated processes to be able to affect
real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
is invoked on a kernel with enabled nohz_full CPUs.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Lai Jiangshan <jiangshanlai@gmail.com>
CC: <stable@vger.kernel.org>	[3.10+]
---
 kernel/membarrier.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/membarrier.c b/kernel/membarrier.c
index 536c727..9f9284f 100644
--- a/kernel/membarrier.c
+++ b/kernel/membarrier.c
@@ -16,6 +16,7 @@
 
 #include <linux/syscalls.h>
 #include <linux/membarrier.h>
+#include <linux/tick.h>
 
 /*
  * Bitmask made from a "or" of all commands within enum membarrier_cmd,
@@ -51,6 +52,9 @@
  */
 SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
 {
+	/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
+	if (tick_nohz_full_enabled())
+		return -ENOSYS;
 	if (unlikely(flags))
 		return -EINVAL;
 	switch (cmd) {
-- 
2.1.4

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#1514741

From"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date2016-11-03 18:50 +0100
Message-ID<szujg-70x-23@gated-at.bofh.it>
In reply to#1514671
On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote:
> Userspace applications should be allowed to expect the membarrier system
> call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
> nohz_full CPUs, but synchronize_sched() does not take those into
> account.
> 
> Given that we do not want unrelated processes to be able to affect
> real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
> is invoked on a kernel with enabled nohz_full CPUs.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

> CC: Josh Triplett <josh@joshtriplett.org>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Lai Jiangshan <jiangshanlai@gmail.com>
> CC: <stable@vger.kernel.org>	[3.10+]
> ---
>  kernel/membarrier.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/membarrier.c b/kernel/membarrier.c
> index 536c727..9f9284f 100644
> --- a/kernel/membarrier.c
> +++ b/kernel/membarrier.c
> @@ -16,6 +16,7 @@
> 
>  #include <linux/syscalls.h>
>  #include <linux/membarrier.h>
> +#include <linux/tick.h>
> 
>  /*
>   * Bitmask made from a "or" of all commands within enum membarrier_cmd,
> @@ -51,6 +52,9 @@
>   */
>  SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
>  {
> +	/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
> +	if (tick_nohz_full_enabled())
> +		return -ENOSYS;
>  	if (unlikely(flags))
>  		return -EINVAL;
>  	switch (cmd) {
> -- 
> 2.1.4
>

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#1516338

FromMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date2016-11-07 18:10 +0100
Message-ID<sAVAK-62m-11@gated-at.bofh.it>
In reply to#1514741
----- On Nov 3, 2016, at 1:49 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote:

> On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote:
>> Userspace applications should be allowed to expect the membarrier system
>> call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
>> nohz_full CPUs, but synchronize_sched() does not take those into
>> account.
>> 
>> Given that we do not want unrelated processes to be able to affect
>> real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
>> is invoked on a kernel with enabled nohz_full CPUs.
>> 
>> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

Hi Paul,

Do you plan to pick it up through your tree, or I should sent
it directly to Linus ?

Thanks,

Mathieu

> 
>> CC: Josh Triplett <josh@joshtriplett.org>
>> CC: Steven Rostedt <rostedt@goodmis.org>
>> CC: Lai Jiangshan <jiangshanlai@gmail.com>
>> CC: <stable@vger.kernel.org>	[3.10+]
>> ---
>>  kernel/membarrier.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>> 
>> diff --git a/kernel/membarrier.c b/kernel/membarrier.c
>> index 536c727..9f9284f 100644
>> --- a/kernel/membarrier.c
>> +++ b/kernel/membarrier.c
>> @@ -16,6 +16,7 @@
>> 
>>  #include <linux/syscalls.h>
>>  #include <linux/membarrier.h>
>> +#include <linux/tick.h>
>> 
>>  /*
>>   * Bitmask made from a "or" of all commands within enum membarrier_cmd,
>> @@ -51,6 +52,9 @@
>>   */
>>  SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
>>  {
>> +	/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
>> +	if (tick_nohz_full_enabled())
>> +		return -ENOSYS;
>>  	if (unlikely(flags))
>>  		return -EINVAL;
>>  	switch (cmd) {
>> --
>> 2.1.4

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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#1516422

FromMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date2016-11-07 19:20 +0100
Message-ID<sAWGu-6RG-33@gated-at.bofh.it>
In reply to#1516338
----- On Nov 7, 2016, at 1:06 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote:

> On Mon, Nov 07, 2016 at 05:08:59PM +0000, Mathieu Desnoyers wrote:
>> ----- On Nov 3, 2016, at 1:49 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com
>> wrote:
>> 
>> > On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote:
>> >> Userspace applications should be allowed to expect the membarrier system
>> >> call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
>> >> nohz_full CPUs, but synchronize_sched() does not take those into
>> >> account.
>> >> 
>> >> Given that we do not want unrelated processes to be able to affect
>> >> real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
>> >> is invoked on a kernel with enabled nohz_full CPUs.
>> >> 
>> >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>> >> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>> > 
>> > Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>> 
>> Hi Paul,
>> 
>> Do you plan to pick it up through your tree, or I should sent
>> it directly to Linus ?
> 
> Your choice.  I believe that the original went some other way, but I
> would be fine carrying this one.

Not sure what you mean by "the original" ? And which other way ?
I have not been notified about this.

If you can carry this patch it would be very much appreciated,

Thanks,

Mathieu

> 
>							Thanx, Paul
> 
>> Thanks,
>> 
>> Mathieu
>> 
>> > 
>> >> CC: Josh Triplett <josh@joshtriplett.org>
>> >> CC: Steven Rostedt <rostedt@goodmis.org>
>> >> CC: Lai Jiangshan <jiangshanlai@gmail.com>
>> >> CC: <stable@vger.kernel.org>	[3.10+]
>> >> ---
>> >>  kernel/membarrier.c | 4 ++++
>> >>  1 file changed, 4 insertions(+)
>> >> 
>> >> diff --git a/kernel/membarrier.c b/kernel/membarrier.c
>> >> index 536c727..9f9284f 100644
>> >> --- a/kernel/membarrier.c
>> >> +++ b/kernel/membarrier.c
>> >> @@ -16,6 +16,7 @@
>> >> 
>> >>  #include <linux/syscalls.h>
>> >>  #include <linux/membarrier.h>
>> >> +#include <linux/tick.h>
>> >> 
>> >>  /*
>> >>   * Bitmask made from a "or" of all commands within enum membarrier_cmd,
>> >> @@ -51,6 +52,9 @@
>> >>   */
>> >>  SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
>> >>  {
>> >> +	/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
>> >> +	if (tick_nohz_full_enabled())
>> >> +		return -ENOSYS;
>> >>  	if (unlikely(flags))
>> >>  		return -EINVAL;
>> >>  	switch (cmd) {
>> >> --
>> >> 2.1.4
>> 
>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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#1516863

From"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date2016-11-08 07:40 +0100
Message-ID<sB8eC-5Nz-23@gated-at.bofh.it>
In reply to#1516422
On Mon, Nov 07, 2016 at 06:10:14PM +0000, Mathieu Desnoyers wrote:
> 
> ----- On Nov 7, 2016, at 1:06 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote:
> 
> > On Mon, Nov 07, 2016 at 05:08:59PM +0000, Mathieu Desnoyers wrote:
> >> ----- On Nov 3, 2016, at 1:49 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com
> >> wrote:
> >> 
> >> > On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote:
> >> >> Userspace applications should be allowed to expect the membarrier system
> >> >> call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
> >> >> nohz_full CPUs, but synchronize_sched() does not take those into
> >> >> account.
> >> >> 
> >> >> Given that we do not want unrelated processes to be able to affect
> >> >> real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
> >> >> is invoked on a kernel with enabled nohz_full CPUs.
> >> >> 
> >> >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> >> >> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> >> > 
> >> > Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> >> 
> >> Hi Paul,
> >> 
> >> Do you plan to pick it up through your tree, or I should sent
> >> it directly to Linus ?
> > 
> > Your choice.  I believe that the original went some other way, but I
> > would be fine carrying this one.
> 
> Not sure what you mean by "the original" ? And which other way ?
> I have not been notified about this.

If I remember correctly, you sent the original sys_membarrier()
patch through akpm or similar.

> If you can carry this patch it would be very much appreciated,

Will do!

							Thanx, Paul

> Thanks,
> 
> Mathieu
> 
> > 
> >							Thanx, Paul
> > 
> >> Thanks,
> >> 
> >> Mathieu
> >> 
> >> > 
> >> >> CC: Josh Triplett <josh@joshtriplett.org>
> >> >> CC: Steven Rostedt <rostedt@goodmis.org>
> >> >> CC: Lai Jiangshan <jiangshanlai@gmail.com>
> >> >> CC: <stable@vger.kernel.org>	[3.10+]
> >> >> ---
> >> >>  kernel/membarrier.c | 4 ++++
> >> >>  1 file changed, 4 insertions(+)
> >> >> 
> >> >> diff --git a/kernel/membarrier.c b/kernel/membarrier.c
> >> >> index 536c727..9f9284f 100644
> >> >> --- a/kernel/membarrier.c
> >> >> +++ b/kernel/membarrier.c
> >> >> @@ -16,6 +16,7 @@
> >> >> 
> >> >>  #include <linux/syscalls.h>
> >> >>  #include <linux/membarrier.h>
> >> >> +#include <linux/tick.h>
> >> >> 
> >> >>  /*
> >> >>   * Bitmask made from a "or" of all commands within enum membarrier_cmd,
> >> >> @@ -51,6 +52,9 @@
> >> >>   */
> >> >>  SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
> >> >>  {
> >> >> +	/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
> >> >> +	if (tick_nohz_full_enabled())
> >> >> +		return -ENOSYS;
> >> >>  	if (unlikely(flags))
> >> >>  		return -EINVAL;
> >> >>  	switch (cmd) {
> >> >> --
> >> >> 2.1.4
> >> 
> >> --
> >> Mathieu Desnoyers
> >> EfficiOS Inc.
> >> http://www.efficios.com
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>

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#1517090

FromMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date2016-11-08 12:20 +0100
Message-ID<sBcBA-bB-29@gated-at.bofh.it>
In reply to#1516863
----- On Nov 7, 2016, at 3:03 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote:

> On Mon, Nov 07, 2016 at 06:10:14PM +0000, Mathieu Desnoyers wrote:
>> 
>> ----- On Nov 7, 2016, at 1:06 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com
>> wrote:
>> 
>> > On Mon, Nov 07, 2016 at 05:08:59PM +0000, Mathieu Desnoyers wrote:
>> >> ----- On Nov 3, 2016, at 1:49 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com
>> >> wrote:
>> >> 
>> >> > On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote:
>> >> >> Userspace applications should be allowed to expect the membarrier system
>> >> >> call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
>> >> >> nohz_full CPUs, but synchronize_sched() does not take those into
>> >> >> account.
>> >> >> 
>> >> >> Given that we do not want unrelated processes to be able to affect
>> >> >> real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
>> >> >> is invoked on a kernel with enabled nohz_full CPUs.
>> >> >> 
>> >> >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>> >> >> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>> >> > 
>> >> > Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>> >> 
>> >> Hi Paul,
>> >> 
>> >> Do you plan to pick it up through your tree, or I should sent
>> >> it directly to Linus ?
>> > 
>> > Your choice.  I believe that the original went some other way, but I
>> > would be fine carrying this one.
>> 
>> Not sure what you mean by "the original" ? And which other way ?
>> I have not been notified about this.
> 
> If I remember correctly, you sent the original sys_membarrier()
> patch through akpm or similar.

Ah right, the original implementation, yes.

> 
>> If you can carry this patch it would be very much appreciated,
> 
> Will do!

Especially since the regression is somewhat related to RCU
behavior wrt nohz_full, getting it through your tree seems
relevant.

Thanks!

Mathieu

> 
>							Thanx, Paul
> 
>> Thanks,
>> 
>> Mathieu
>> 
>> > 
>> >							Thanx, Paul
>> > 
>> >> Thanks,
>> >> 
>> >> Mathieu
>> >> 
>> >> > 
>> >> >> CC: Josh Triplett <josh@joshtriplett.org>
>> >> >> CC: Steven Rostedt <rostedt@goodmis.org>
>> >> >> CC: Lai Jiangshan <jiangshanlai@gmail.com>
>> >> >> CC: <stable@vger.kernel.org>	[3.10+]
>> >> >> ---
>> >> >>  kernel/membarrier.c | 4 ++++
>> >> >>  1 file changed, 4 insertions(+)
>> >> >> 
>> >> >> diff --git a/kernel/membarrier.c b/kernel/membarrier.c
>> >> >> index 536c727..9f9284f 100644
>> >> >> --- a/kernel/membarrier.c
>> >> >> +++ b/kernel/membarrier.c
>> >> >> @@ -16,6 +16,7 @@
>> >> >> 
>> >> >>  #include <linux/syscalls.h>
>> >> >>  #include <linux/membarrier.h>
>> >> >> +#include <linux/tick.h>
>> >> >> 
>> >> >>  /*
>> >> >>   * Bitmask made from a "or" of all commands within enum membarrier_cmd,
>> >> >> @@ -51,6 +52,9 @@
>> >> >>   */
>> >> >>  SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
>> >> >>  {
>> >> >> +	/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
>> >> >> +	if (tick_nohz_full_enabled())
>> >> >> +		return -ENOSYS;
>> >> >>  	if (unlikely(flags))
>> >> >>  		return -EINVAL;
>> >> >>  	switch (cmd) {
>> >> >> --
>> >> >> 2.1.4
>> >> 
>> >> --
>> >> Mathieu Desnoyers
>> >> EfficiOS Inc.
>> >> http://www.efficios.com
>> 
>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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#1516533

From"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date2016-11-07 20:30 +0100
Message-ID<sAWGu-6RG-35@gated-at.bofh.it>
In reply to#1516338
On Mon, Nov 07, 2016 at 05:08:59PM +0000, Mathieu Desnoyers wrote:
> ----- On Nov 3, 2016, at 1:49 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote:
> 
> > On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote:
> >> Userspace applications should be allowed to expect the membarrier system
> >> call with MEMBARRIER_CMD_SHARED command to issue memory barriers on
> >> nohz_full CPUs, but synchronize_sched() does not take those into
> >> account.
> >> 
> >> Given that we do not want unrelated processes to be able to affect
> >> real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier
> >> is invoked on a kernel with enabled nohz_full CPUs.
> >> 
> >> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> >> CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > 
> > Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> Hi Paul,
> 
> Do you plan to pick it up through your tree, or I should sent
> it directly to Linus ?

Your choice.  I believe that the original went some other way, but I
would be fine carrying this one.

							Thanx, Paul

> Thanks,
> 
> Mathieu
> 
> > 
> >> CC: Josh Triplett <josh@joshtriplett.org>
> >> CC: Steven Rostedt <rostedt@goodmis.org>
> >> CC: Lai Jiangshan <jiangshanlai@gmail.com>
> >> CC: <stable@vger.kernel.org>	[3.10+]
> >> ---
> >>  kernel/membarrier.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >> 
> >> diff --git a/kernel/membarrier.c b/kernel/membarrier.c
> >> index 536c727..9f9284f 100644
> >> --- a/kernel/membarrier.c
> >> +++ b/kernel/membarrier.c
> >> @@ -16,6 +16,7 @@
> >> 
> >>  #include <linux/syscalls.h>
> >>  #include <linux/membarrier.h>
> >> +#include <linux/tick.h>
> >> 
> >>  /*
> >>   * Bitmask made from a "or" of all commands within enum membarrier_cmd,
> >> @@ -51,6 +52,9 @@
> >>   */
> >>  SYSCALL_DEFINE2(membarrier, int, cmd, int, flags)
> >>  {
> >> +	/* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */
> >> +	if (tick_nohz_full_enabled())
> >> +		return -ENOSYS;
> >>  	if (unlikely(flags))
> >>  		return -EINVAL;
> >>  	switch (cmd) {
> >> --
> >> 2.1.4
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>

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