[PATCH V5] futex: set FLAGS_HAS_TIMEOUT during futex_wait restart setup

[PATCH V5] futex: set FLAGS_HAS_TIMEOUT during futex_wait restart setup

[Darren Hart]

The FLAGS_HAS_TIMEOUT flag was not getting set, causing the restart_block to
restart futex_wait() without a timeout after a signal.

Commit b41277dc7a18ee332d in 2.6.38 introduced the regression by accidentally
removing the the FLAGS_HAS_TIMEOUT assignment from futex_wait() during the setup
of the restart block. Restore the originaly behavior.

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=32922

V2: Added references to commit message.
V3: Set flag during restart block instead of do_futex()
V4: Correct stupid order of assignment mistake pointed out by Eric
V5: Correct subject to match implementation, correct stable submission

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Reported-by: Tim Smith <tsmith201104@yahoo.com>
Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: John Kacur <jkacur@redhat.com>
Cc: stable@kernel.org
---
 kernel/futex.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index bda4157..abd5324 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1886,7 +1886,7 @@ retry:
 	restart->futex.val = val;
 	restart->futex.time = abs_time->tv64;
 	restart->futex.bitset = bitset;
-	restart->futex.flags = flags;
+	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
 
 	ret = -ERESTART_RESTARTBLOCK;
 
-- 
1.7.1

Re: [PATCH V5] futex: set FLAGS_HAS_TIMEOUT during futex_wait restart setup

[Thomas Gleixner]

On Thu, 14 Apr 2011, Darren Hart wrote:

> The FLAGS_HAS_TIMEOUT flag was not getting set, causing the restart_block to
> restart futex_wait() without a timeout after a signal.
> 
> Commit b41277dc7a18ee332d in 2.6.38 introduced the regression by accidentally
> removing the the FLAGS_HAS_TIMEOUT assignment from futex_wait() during the setup
> of the restart block. Restore the originaly behavior.
> 
> Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=32922
> 
> V2: Added references to commit message.
> V3: Set flag during restart block instead of do_futex()
> V4: Correct stupid order of assignment mistake pointed out by Eric
> V5: Correct subject to match implementation, correct stable submission
> 
> Signed-off-by: Darren Hart <dvhart@linux.intel.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Reported-by: Tim Smith <tsmith201104@yahoo.com>
> Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: John Kacur <jkacur@redhat.com>
> Cc: stable@kernel.org
> ---
>  kernel/futex.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index bda4157..abd5324 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1886,7 +1886,7 @@ retry:
>  	restart->futex.val = val;
>  	restart->futex.time = abs_time->tv64;
>  	restart->futex.bitset = bitset;
> -	restart->futex.flags = flags;
> +	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;

We only get here when a timeout is pending. So why don't we just do
the obvious:

--- linux-2.6.orig/kernel/futex.c
+++ linux-2.6/kernel/futex.c
@@ -1902,16 +1902,13 @@ out:
 static long futex_wait_restart(struct restart_block *restart)
 {
 	u32 __user *uaddr = restart->futex.uaddr;
-	ktime_t t, *tp = NULL;
+	ktime_t t;
 
-	if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
-		t.tv64 = restart->futex.time;
-		tp = &t;
-	}
+	t.tv64 = restart->futex.time;
 	restart->fn = do_no_restart_syscall;
 
 	return (long)futex_wait(uaddr, restart->futex.flags,
-				restart->futex.val, tp, restart->futex.bitset);
+				restart->futex.val, &t, restart->futex.bitset);
 }
 
Thanks,

	tglx

Re: [PATCH V5] futex: set FLAGS_HAS_TIMEOUT during futex_wait restart setup

[Eric Dumazet]

Le vendredi 15 avril 2011 à 10:33 +0200, Thomas Gleixner a écrit :
> On Thu, 14 Apr 2011, Darren Hart wrote:
> 
> > The FLAGS_HAS_TIMEOUT flag was not getting set, causing the restart_block to
> > restart futex_wait() without a timeout after a signal.
> > 
> > Commit b41277dc7a18ee332d in 2.6.38 introduced the regression by accidentally
> > removing the the FLAGS_HAS_TIMEOUT assignment from futex_wait() during the setup
> > of the restart block. Restore the originaly behavior.
> > 
> > Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=32922
> > 
> > V2: Added references to commit message.
> > V3: Set flag during restart block instead of do_futex()
> > V4: Correct stupid order of assignment mistake pointed out by Eric
> > V5: Correct subject to match implementation, correct stable submission
> > 
> > Signed-off-by: Darren Hart <dvhart@linux.intel.com>
> > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> > Reported-by: Tim Smith <tsmith201104@yahoo.com>
> > Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Ingo Molnar <mingo@elte.hu>
> > Cc: John Kacur <jkacur@redhat.com>
> > Cc: stable@kernel.org
> > ---
> >  kernel/futex.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/kernel/futex.c b/kernel/futex.c
> > index bda4157..abd5324 100644
> > --- a/kernel/futex.c
> > +++ b/kernel/futex.c
> > @@ -1886,7 +1886,7 @@ retry:
> >  	restart->futex.val = val;
> >  	restart->futex.time = abs_time->tv64;
> >  	restart->futex.bitset = bitset;
> > -	restart->futex.flags = flags;
> > +	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
> 
> We only get here when a timeout is pending. So why don't we just do
> the obvious:
> 
> --- linux-2.6.orig/kernel/futex.c
> +++ linux-2.6/kernel/futex.c
> @@ -1902,16 +1902,13 @@ out:
>  static long futex_wait_restart(struct restart_block *restart)
>  {
>  	u32 __user *uaddr = restart->futex.uaddr;
> -	ktime_t t, *tp = NULL;
> +	ktime_t t;
>  
> -	if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
> -		t.tv64 = restart->futex.time;
> -		tp = &t;
> -	}
> +	t.tv64 = restart->futex.time;
>  	restart->fn = do_no_restart_syscall;
>  
>  	return (long)futex_wait(uaddr, restart->futex.flags,
> -				restart->futex.val, tp, restart->futex.bitset);
> +				restart->futex.val, &t, restart->futex.bitset);
>  }
>  

Because its not suitable for stable ?

This is basically reverting a72188d8a64ebe74, so why do you keep
FUTEX_HAS_TIMEOUT definition ?

Re: [PATCH V5] futex: set FLAGS_HAS_TIMEOUT during futex_wait restart setup

[Darren Hart]

On 04/15/2011 01:33 AM, Thomas Gleixner wrote:
> On Thu, 14 Apr 2011, Darren Hart wrote:
> 
>> The FLAGS_HAS_TIMEOUT flag was not getting set, causing the restart_block to
>> restart futex_wait() without a timeout after a signal.
>>
>> Commit b41277dc7a18ee332d in 2.6.38 introduced the regression by accidentally
>> removing the the FLAGS_HAS_TIMEOUT assignment from futex_wait() during the setup
>> of the restart block. Restore the originaly behavior.
>>
>> Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=32922
>>
>> V2: Added references to commit message.
>> V3: Set flag during restart block instead of do_futex()
>> V4: Correct stupid order of assignment mistake pointed out by Eric
>> V5: Correct subject to match implementation, correct stable submission
>>
>> Signed-off-by: Darren Hart <dvhart@linux.intel.com>
>> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
>> Reported-by: Tim Smith <tsmith201104@yahoo.com>
>> Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Ingo Molnar <mingo@elte.hu>
>> Cc: John Kacur <jkacur@redhat.com>
>> Cc: stable@kernel.org
>> ---
>>  kernel/futex.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/futex.c b/kernel/futex.c
>> index bda4157..abd5324 100644
>> --- a/kernel/futex.c
>> +++ b/kernel/futex.c
>> @@ -1886,7 +1886,7 @@ retry:
>>  	restart->futex.val = val;
>>  	restart->futex.time = abs_time->tv64;
>>  	restart->futex.bitset = bitset;
>> -	restart->futex.flags = flags;
>> +	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
> 
> We only get here when a timeout is pending. So why don't we just do
> the obvious:
> 
> --- linux-2.6.orig/kernel/futex.c
> +++ linux-2.6/kernel/futex.c
> @@ -1902,16 +1902,13 @@ out:
>  static long futex_wait_restart(struct restart_block *restart)
>  {
>  	u32 __user *uaddr = restart->futex.uaddr;
> -	ktime_t t, *tp = NULL;
> +	ktime_t t;
>  
> -	if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
> -		t.tv64 = restart->futex.time;
> -		tp = &t;
> -	}
> +	t.tv64 = restart->futex.time;
>  	restart->fn = do_no_restart_syscall;
>  
>  	return (long)futex_wait(uaddr, restart->futex.flags,
> -				restart->futex.val, tp, restart->futex.bitset);
> +				restart->futex.val, &t, restart->futex.bitset);
>  }

I believe I asked you the same question when I was adding the
FLAGS_HAS_TIMEOUT. :-) The problem is distinguishing between no timeout
and an expired timer. The above always passes a non-null address for
abs_time to futex_wait(), which will then always schedule a timer.

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel

Re: [PATCH V5] futex: set FLAGS_HAS_TIMEOUT during futex_wait restart setup

[Thomas Gleixner]

On Fri, 15 Apr 2011, Darren Hart wrote:
> I believe I asked you the same question when I was adding the
> FLAGS_HAS_TIMEOUT. :-) The problem is distinguishing between no timeout
> and an expired timer. The above always passes a non-null address for
> abs_time to futex_wait(), which will then always schedule a timer.

Duh, correct.