Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On Tue, Feb 12, 2008 at 08:46:30PM +0100, Jarek Poplawski wrote: > On Tue, Feb 12, 2008 at 08:32:18PM +0100, Jarek Poplawski wrote: > ... > > It seems the above version of this macro uses the barrier for 0, but > > if I miss something, or for these other: documenting reasons, > > ...or __builtin_constants could be used for indexing (?!), Yep. For example: elem[0].next = 1; rcu_assign_index(global_index, 0); Thanx, Paul > > then of > > course you are right. > > Jarek P. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On Tue, Feb 12, 2008 at 08:46:30PM +0100, Jarek Poplawski wrote: On Tue, Feb 12, 2008 at 08:32:18PM +0100, Jarek Poplawski wrote: ... It seems the above version of this macro uses the barrier for 0, but if I miss something, or for these other: documenting reasons, ...or __builtin_constants could be used for indexing (?!), Yep. For example: elem[0].next = 1; rcu_assign_index(global_index, 0); Thanx, Paul then of course you are right. Jarek P. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On Tue, Feb 12, 2008 at 08:32:18PM +0100, Jarek Poplawski wrote: ... > It seems the above version of this macro uses the barrier for 0, but > if I miss something, or for these other: documenting reasons, ...or __builtin_constants could be used for indexing (?!), > then of > course you are right. Jarek P. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On Tue, Feb 12, 2008 at 08:07:29AM -0800, Paul E. McKenney wrote:
...
> "All programmers are blind, especially me."
Hmm... I got it my way: you - superheroes - sometimes seem to be just
like us - common people... (Probably early in the morning, before
dressing your funny costumes?)
> You are right, Jarek. I ran this through gcc, and the following
> comes close:
>
> #define rcu_assign_pointer(p, v) \
> ({ \
> if (!__builtin_constant_p(v) || (v)) \
> smp_wmb(); \
> (p) = (v); \
> })
>
> But I am concerned about the following case:
>
> rcu_assign_pointer(global_index, 0);
>
> . . .
>
> x = global_array[rcu_dereference(global_index)];
>
> Since arrays have a zero-th element, we would really want a memory
> barrier in this case.
It seems the above version of this macro uses the barrier for 0, but
if I miss something, or for these other: documenting reasons, then of
course you are right.
>
> So how about leaving the index-unfriendly version of rcu_assign_pointer()
> and adding an rcu_assign_index() as follows?
>
> Thanx, Paul
>
> Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]>
> ---
>
> rcupdate.h | 18 ++
> 1 file changed, 18 insertions(+)
>
> diff -urpNa -X dontdiff linux-2.6.24/include/linux/rcupdate.h
> linux-2.6.24-rai/include/linux/rcupdate.h
> --- linux-2.6.24/include/linux/rcupdate.h 2008-01-24 14:58:37.0
> -0800
> +++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-12 08:04:59.0
> -0800
> @@ -278,6 +278,24 @@ extern struct lockdep_map rcu_lock_map;
> })
>
> /**
> + * rcu_assign_index - assign (publicize) a index of a newly
> + * initialized array elementg that will be dereferenced by RCU
---^
+ * initialized array element that will be dereferenced by RCU
Regards,
Jarek P.
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Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On Tue, Feb 12, 2008 at 08:57:14AM +, Jarek Poplawski wrote:
> On 12-02-2008 02:16, David Miller wrote:
> > From: Stephen Hemminger <[EMAIL PROTECTED]>
> > Date: Mon, 11 Feb 2008 16:59:54 -0800
> >
> > linux-kernel added to CC:, any change to generic kernel infrastructure
> > should be posted there
> >
> >> Eliminate warnings when rcu_assign_pointer is used with unsigned long.
> >> It is reasonable to use RCU with non-pointer values so allow it for general
> >> use. Add a comment to explain the if test.
> >>
> >> Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]>
> >> ---
> >> include/linux/rcupdate.h | 13 +++--
> >> 1 files changed, 7 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> >> index 37a642c..c44ac87 100644
> >> --- a/include/linux/rcupdate.h
> >> +++ b/include/linux/rcupdate.h
> >> @@ -172,14 +172,15 @@ struct rcu_head {
> >> * structure after the pointer assignment. More importantly, this
> >> * call documents which pointers will be dereferenced by RCU read-side
> >> * code.
> >> + *
> >> + * If value is the NULL (constant 0), then no barrier is needed.
> >> */
> >>
> >> -#define rcu_assign_pointer(p, v) \
> >> - ({ \
> >> - if (!__builtin_constant_p(v) || \
> >> - ((v) != NULL)) \
> >> - smp_wmb(); \
> >> - (p) = (v); \
> >> +#define rcu_assign_pointer(p, v) \
> >> + ({ \
> >> + if (!(__builtin_constant_p(v) && v))\
>
> ...But, "If value is the NULL (constant 0)" we have:
>
> if (!(1 && NULL != 0)) ==> if (!(0)) and the barrier is used?!
"All programmers are blind, especially me."
You are right, Jarek. I ran this through gcc, and the following
comes close:
#define rcu_assign_pointer(p, v) \
({ \
if (!__builtin_constant_p(v) || (v)) \
smp_wmb(); \
(p) = (v); \
})
But I am concerned about the following case:
rcu_assign_pointer(global_index, 0);
. . .
x = global_array[rcu_dereference(global_index)];
Since arrays have a zero-th element, we would really want a memory
barrier in this case.
So how about leaving the index-unfriendly version of rcu_assign_pointer()
and adding an rcu_assign_index() as follows?
Thanx, Paul
Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]>
---
rcupdate.h | 18 ++
1 file changed, 18 insertions(+)
diff -urpNa -X dontdiff linux-2.6.24/include/linux/rcupdate.h
linux-2.6.24-rai/include/linux/rcupdate.h
--- linux-2.6.24/include/linux/rcupdate.h 2008-01-24 14:58:37.0
-0800
+++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-12 08:04:59.0
-0800
@@ -278,6 +278,24 @@ extern struct lockdep_map rcu_lock_map;
})
/**
+ * rcu_assign_index - assign (publicize) a index of a newly
+ * initialized array elementg that will be dereferenced by RCU
+ * read-side critical sections. Returns the value assigned.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (pretty much all of them other than x86), and also prevents
+ * the compiler from reordering the code that initializes the
+ * structure after the index assignment. More importantly, this
+ * call documents which indexes will be dereferenced by RCU read-side
+ * code.
+ */
+
+#define rcu_assign_index(p, v) ({ \
+ smp_wmb(); \
+ (p) = (v); \
+ })
+
+/**
* synchronize_sched - block until all CPUs have exited any non-preemptive
* kernel code sequences.
*
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Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On 12-02-2008 02:16, David Miller wrote:
> From: Stephen Hemminger <[EMAIL PROTECTED]>
> Date: Mon, 11 Feb 2008 16:59:54 -0800
>
> linux-kernel added to CC:, any change to generic kernel infrastructure
> should be posted there
>
>> Eliminate warnings when rcu_assign_pointer is used with unsigned long.
>> It is reasonable to use RCU with non-pointer values so allow it for general
>> use. Add a comment to explain the if test.
>>
>> Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]>
>> ---
>> include/linux/rcupdate.h | 13 +++--
>> 1 files changed, 7 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
>> index 37a642c..c44ac87 100644
>> --- a/include/linux/rcupdate.h
>> +++ b/include/linux/rcupdate.h
>> @@ -172,14 +172,15 @@ struct rcu_head {
>> * structure after the pointer assignment. More importantly, this
>> * call documents which pointers will be dereferenced by RCU read-side
>> * code.
>> + *
>> + * If value is the NULL (constant 0), then no barrier is needed.
>> */
>>
>> -#define rcu_assign_pointer(p, v) \
>> -({ \
>> -if (!__builtin_constant_p(v) || \
>> -((v) != NULL)) \
>> -smp_wmb(); \
>> -(p) = (v); \
>> +#define rcu_assign_pointer(p, v)\
>> +({ \
>> +if (!(__builtin_constant_p(v) && v))\
...But, "If value is the NULL (constant 0)" we have:
if (!(1 && NULL != 0)) ==> if (!(0)) and the barrier is used?!
>> +smp_wmb(); \
>> +(p) = (v); \
>> })
>>
>> /**
Regards,
Jarek P.
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Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On 12-02-2008 02:16, David Miller wrote:
From: Stephen Hemminger [EMAIL PROTECTED]
Date: Mon, 11 Feb 2008 16:59:54 -0800
linux-kernel added to CC:, any change to generic kernel infrastructure
should be posted there
Eliminate warnings when rcu_assign_pointer is used with unsigned long.
It is reasonable to use RCU with non-pointer values so allow it for general
use. Add a comment to explain the if test.
Signed-off-by: Stephen Hemminger [EMAIL PROTECTED]
---
include/linux/rcupdate.h | 13 +++--
1 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 37a642c..c44ac87 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -172,14 +172,15 @@ struct rcu_head {
* structure after the pointer assignment. More importantly, this
* call documents which pointers will be dereferenced by RCU read-side
* code.
+ *
+ * If value is the NULL (constant 0), then no barrier is needed.
*/
-#define rcu_assign_pointer(p, v) \
-({ \
-if (!__builtin_constant_p(v) || \
-((v) != NULL)) \
-smp_wmb(); \
-(p) = (v); \
+#define rcu_assign_pointer(p, v)\
+({ \
+if (!(__builtin_constant_p(v) v))\
...But, If value is the NULL (constant 0) we have:
if (!(1 NULL != 0)) == if (!(0)) and the barrier is used?!
+smp_wmb(); \
+(p) = (v); \
})
/**
Regards,
Jarek P.
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Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On Tue, Feb 12, 2008 at 08:32:18PM +0100, Jarek Poplawski wrote: ... It seems the above version of this macro uses the barrier for 0, but if I miss something, or for these other: documenting reasons, ...or __builtin_constants could be used for indexing (?!), then of course you are right. Jarek P. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
On Tue, Feb 12, 2008 at 08:57:14AM +, Jarek Poplawski wrote:
On 12-02-2008 02:16, David Miller wrote:
From: Stephen Hemminger [EMAIL PROTECTED]
Date: Mon, 11 Feb 2008 16:59:54 -0800
linux-kernel added to CC:, any change to generic kernel infrastructure
should be posted there
Eliminate warnings when rcu_assign_pointer is used with unsigned long.
It is reasonable to use RCU with non-pointer values so allow it for general
use. Add a comment to explain the if test.
Signed-off-by: Stephen Hemminger [EMAIL PROTECTED]
---
include/linux/rcupdate.h | 13 +++--
1 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 37a642c..c44ac87 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -172,14 +172,15 @@ struct rcu_head {
* structure after the pointer assignment. More importantly, this
* call documents which pointers will be dereferenced by RCU read-side
* code.
+ *
+ * If value is the NULL (constant 0), then no barrier is needed.
*/
-#define rcu_assign_pointer(p, v) \
- ({ \
- if (!__builtin_constant_p(v) || \
- ((v) != NULL)) \
- smp_wmb(); \
- (p) = (v); \
+#define rcu_assign_pointer(p, v) \
+ ({ \
+ if (!(__builtin_constant_p(v) v))\
...But, If value is the NULL (constant 0) we have:
if (!(1 NULL != 0)) == if (!(0)) and the barrier is used?!
All programmers are blind, especially me.
You are right, Jarek. I ran this through gcc, and the following
comes close:
#define rcu_assign_pointer(p, v) \
({ \
if (!__builtin_constant_p(v) || (v)) \
smp_wmb(); \
(p) = (v); \
})
But I am concerned about the following case:
rcu_assign_pointer(global_index, 0);
. . .
x = global_array[rcu_dereference(global_index)];
Since arrays have a zero-th element, we would really want a memory
barrier in this case.
So how about leaving the index-unfriendly version of rcu_assign_pointer()
and adding an rcu_assign_index() as follows?
Thanx, Paul
Signed-off-by: Paul E. McKenney [EMAIL PROTECTED]
---
rcupdate.h | 18 ++
1 file changed, 18 insertions(+)
diff -urpNa -X dontdiff linux-2.6.24/include/linux/rcupdate.h
linux-2.6.24-rai/include/linux/rcupdate.h
--- linux-2.6.24/include/linux/rcupdate.h 2008-01-24 14:58:37.0
-0800
+++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-12 08:04:59.0
-0800
@@ -278,6 +278,24 @@ extern struct lockdep_map rcu_lock_map;
})
/**
+ * rcu_assign_index - assign (publicize) a index of a newly
+ * initialized array elementg that will be dereferenced by RCU
+ * read-side critical sections. Returns the value assigned.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (pretty much all of them other than x86), and also prevents
+ * the compiler from reordering the code that initializes the
+ * structure after the index assignment. More importantly, this
+ * call documents which indexes will be dereferenced by RCU read-side
+ * code.
+ */
+
+#define rcu_assign_index(p, v) ({ \
+ smp_wmb(); \
+ (p) = (v); \
+ })
+
+/**
* synchronize_sched - block until all CPUs have exited any non-preemptive
* kernel code sequences.
*
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Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
From: "Paul E. McKenney" <[EMAIL PROTECTED]> Date: Mon, 11 Feb 2008 17:27:41 -0800 > On Mon, Feb 11, 2008 at 04:59:54PM -0800, Stephen Hemminger wrote: > > Eliminate warnings when rcu_assign_pointer is used with unsigned long. > > It is reasonable to use RCU with non-pointer values so allow it for general > > use. Add a comment to explain the if test. > > Good catch!!! (An apologies for the hassle!!!) > > Acked-by: Paul E. McKenney <[EMAIL PROTECTED]> Thanks for reviewing Paul, I'll apply this. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
From: Stephen Hemminger <[EMAIL PROTECTED]>
Date: Mon, 11 Feb 2008 16:59:54 -0800
linux-kernel added to CC:, any change to generic kernel infrastructure
should be posted there
> Eliminate warnings when rcu_assign_pointer is used with unsigned long.
> It is reasonable to use RCU with non-pointer values so allow it for general
> use. Add a comment to explain the if test.
>
> Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]>
> ---
> include/linux/rcupdate.h | 13 +++--
> 1 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 37a642c..c44ac87 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -172,14 +172,15 @@ struct rcu_head {
> * structure after the pointer assignment. More importantly, this
> * call documents which pointers will be dereferenced by RCU read-side
> * code.
> + *
> + * If value is the NULL (constant 0), then no barrier is needed.
> */
>
> -#define rcu_assign_pointer(p, v) \
> - ({ \
> - if (!__builtin_constant_p(v) || \
> - ((v) != NULL)) \
> - smp_wmb(); \
> - (p) = (v); \
> +#define rcu_assign_pointer(p, v) \
> + ({ \
> + if (!(__builtin_constant_p(v) && v))\
> + smp_wmb(); \
> + (p) = (v); \
> })
>
> /**
> --
> 1.5.3.8
>
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[PATCH] fib_trie: rcu_assign_pointer warning fix
Eliminate warnings when rcu_assign_pointer is used with unsigned long.
It is reasonable to use RCU with non-pointer values so allow it for general
use. Add a comment to explain the if test.
Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]>
---
include/linux/rcupdate.h | 13 +++--
1 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 37a642c..c44ac87 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -172,14 +172,15 @@ struct rcu_head {
* structure after the pointer assignment. More importantly, this
* call documents which pointers will be dereferenced by RCU read-side
* code.
+ *
+ * If value is the NULL (constant 0), then no barrier is needed.
*/
-#define rcu_assign_pointer(p, v) \
- ({ \
- if (!__builtin_constant_p(v) || \
- ((v) != NULL)) \
- smp_wmb(); \
- (p) = (v); \
+#define rcu_assign_pointer(p, v) \
+ ({ \
+ if (!(__builtin_constant_p(v) && v))\
+ smp_wmb(); \
+ (p) = (v); \
})
/**
--
1.5.3.8
--
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Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
From: Paul E. McKenney [EMAIL PROTECTED] Date: Mon, 11 Feb 2008 17:27:41 -0800 On Mon, Feb 11, 2008 at 04:59:54PM -0800, Stephen Hemminger wrote: Eliminate warnings when rcu_assign_pointer is used with unsigned long. It is reasonable to use RCU with non-pointer values so allow it for general use. Add a comment to explain the if test. Good catch!!! (An apologies for the hassle!!!) Acked-by: Paul E. McKenney [EMAIL PROTECTED] Thanks for reviewing Paul, I'll apply this. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] fib_trie: rcu_assign_pointer warning fix
From: Stephen Hemminger [EMAIL PROTECTED]
Date: Mon, 11 Feb 2008 16:59:54 -0800
linux-kernel added to CC:, any change to generic kernel infrastructure
should be posted there
Eliminate warnings when rcu_assign_pointer is used with unsigned long.
It is reasonable to use RCU with non-pointer values so allow it for general
use. Add a comment to explain the if test.
Signed-off-by: Stephen Hemminger [EMAIL PROTECTED]
---
include/linux/rcupdate.h | 13 +++--
1 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 37a642c..c44ac87 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -172,14 +172,15 @@ struct rcu_head {
* structure after the pointer assignment. More importantly, this
* call documents which pointers will be dereferenced by RCU read-side
* code.
+ *
+ * If value is the NULL (constant 0), then no barrier is needed.
*/
-#define rcu_assign_pointer(p, v) \
- ({ \
- if (!__builtin_constant_p(v) || \
- ((v) != NULL)) \
- smp_wmb(); \
- (p) = (v); \
+#define rcu_assign_pointer(p, v) \
+ ({ \
+ if (!(__builtin_constant_p(v) v))\
+ smp_wmb(); \
+ (p) = (v); \
})
/**
--
1.5.3.8
--
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[PATCH] fib_trie: rcu_assign_pointer warning fix
Eliminate warnings when rcu_assign_pointer is used with unsigned long.
It is reasonable to use RCU with non-pointer values so allow it for general
use. Add a comment to explain the if test.
Signed-off-by: Stephen Hemminger [EMAIL PROTECTED]
---
include/linux/rcupdate.h | 13 +++--
1 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 37a642c..c44ac87 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -172,14 +172,15 @@ struct rcu_head {
* structure after the pointer assignment. More importantly, this
* call documents which pointers will be dereferenced by RCU read-side
* code.
+ *
+ * If value is the NULL (constant 0), then no barrier is needed.
*/
-#define rcu_assign_pointer(p, v) \
- ({ \
- if (!__builtin_constant_p(v) || \
- ((v) != NULL)) \
- smp_wmb(); \
- (p) = (v); \
+#define rcu_assign_pointer(p, v) \
+ ({ \
+ if (!(__builtin_constant_p(v) v))\
+ smp_wmb(); \
+ (p) = (v); \
})
/**
--
1.5.3.8
--
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