Re: [PATCH 2/2] add rcu_assign_index() if ever needed
On Thu, Feb 14, 2008 at 09:02:09AM +0530, Gautham R Shenoy wrote:
On Wed, Feb 13, 2008 at 02:05:15PM -0800, Paul E. McKenney wrote:
Hello again!
This is a speculative patch that as far as I can tell is not yet required.
If anyone applies RCU to a data structure allocated out of an array, using
array indexes in place of pointers to link the array elements together,
then the rcu_assign_index() function in this patch will be needed to
assign a given element's array index to the RCU-traversed index. The
implementation is exactly that of the old rcu_assign_pointer(), so is
extremely well tested.
The existing rcu_assign_pointer() will emit a compiler warning in cases
where rcu_assign_index() is required.
Signed-off-by: Paul E. McKenney [EMAIL PROTECTED]
---
rcupdate.h | 18 ++
1 file changed, 18 insertions(+)
diff -urpNa -X dontdiff linux-2.6.24-rap/include/linux/rcupdate.h
linux-2.6.24-rai/include/linux/rcupdate.h
--- linux-2.6.24-rap/include/linux/rcupdate.h 2008-02-13
13:36:47.0 -0800
+++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-13
10:55:40.0 -0800
@@ -286,6 +286,24 @@ 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
I hope Andrew got that one while porting against the latest -mm :)
Looks good otherwise.
Good catch!!!
Thanx, Paul
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Re: [PATCH 2/2] add rcu_assign_index() if ever needed
On Wed, 13 Feb 2008 14:05:15 -0800 Paul E. McKenney wrote:
Hello again!
This is a speculative patch that as far as I can tell is not yet required.
If anyone applies RCU to a data structure allocated out of an array, using
array indexes in place of pointers to link the array elements together,
then the rcu_assign_index() function in this patch will be needed to
assign a given element's array index to the RCU-traversed index. The
implementation is exactly that of the old rcu_assign_pointer(), so is
extremely well tested.
The existing rcu_assign_pointer() will emit a compiler warning in cases
where rcu_assign_index() is required.
Signed-off-by: Paul E. McKenney [EMAIL PROTECTED]
---
rcupdate.h | 18 ++
1 file changed, 18 insertions(+)
diff -urpNa -X dontdiff linux-2.6.24-rap/include/linux/rcupdate.h
linux-2.6.24-rai/include/linux/rcupdate.h
--- linux-2.6.24-rap/include/linux/rcupdate.h 2008-02-13 13:36:47.0
-0800
+++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-13 10:55:40.0
-0800
@@ -286,6 +286,24 @@ 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.
+ */
s/a index/index/
Along with Gautham's typo fix, you could also make this be passable
kernel-doc notation. :)
See Documentation/kernel-doc-nano-HOWTO.txt for details.
Summary:
The function (or macro) name and short description must be on one line.
This is followed by the parameters, then a blank (actually *) line,
then any (longer) description, notes, etc. So basically:
/**
* rcu_assign_index - assign (publicize) index of a newly initialized array
element
* @p: description of @p
* @v: description of @v
*
* This function assigns (publicizes) the index of a newly
* initialized array element 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.
*
---
~Randy
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Re: [PATCH 2/2] add rcu_assign_index() if ever needed
On Thu, Feb 14, 2008 at 09:24:27AM -0800, Randy Dunlap wrote:
On Wed, 13 Feb 2008 14:05:15 -0800 Paul E. McKenney wrote:
Hello again!
This is a speculative patch that as far as I can tell is not yet required.
If anyone applies RCU to a data structure allocated out of an array, using
array indexes in place of pointers to link the array elements together,
then the rcu_assign_index() function in this patch will be needed to
assign a given element's array index to the RCU-traversed index. The
implementation is exactly that of the old rcu_assign_pointer(), so is
extremely well tested.
The existing rcu_assign_pointer() will emit a compiler warning in cases
where rcu_assign_index() is required.
Signed-off-by: Paul E. McKenney [EMAIL PROTECTED]
---
rcupdate.h | 18 ++
1 file changed, 18 insertions(+)
diff -urpNa -X dontdiff linux-2.6.24-rap/include/linux/rcupdate.h
linux-2.6.24-rai/include/linux/rcupdate.h
--- linux-2.6.24-rap/include/linux/rcupdate.h 2008-02-13
13:36:47.0 -0800
+++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-13
10:55:40.0 -0800
@@ -286,6 +286,24 @@ 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.
+ */
s/a index/index/
Along with Gautham's typo fix, you could also make this be passable
kernel-doc notation. :)
Guess I should do the same for rcu_assign_pointer() and probably several
others as well... Good catch!!!
Thanx, Paul
See Documentation/kernel-doc-nano-HOWTO.txt for details.
Summary:
The function (or macro) name and short description must be on one line.
This is followed by the parameters, then a blank (actually *) line,
then any (longer) description, notes, etc. So basically:
/**
* rcu_assign_index - assign (publicize) index of a newly initialized array
element
* @p: description of @p
* @v: description of @v
*
* This function assigns (publicizes) the index of a newly
* initialized array element 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.
*
---
~Randy
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[PATCH 2/2] add rcu_assign_index() if ever needed
Hello again!
This is a speculative patch that as far as I can tell is not yet required.
If anyone applies RCU to a data structure allocated out of an array, using
array indexes in place of pointers to link the array elements together,
then the rcu_assign_index() function in this patch will be needed to
assign a given element's array index to the RCU-traversed index. The
implementation is exactly that of the old rcu_assign_pointer(), so is
extremely well tested.
The existing rcu_assign_pointer() will emit a compiler warning in cases
where rcu_assign_index() is required.
Signed-off-by: Paul E. McKenney [EMAIL PROTECTED]
---
rcupdate.h | 18 ++
1 file changed, 18 insertions(+)
diff -urpNa -X dontdiff linux-2.6.24-rap/include/linux/rcupdate.h
linux-2.6.24-rai/include/linux/rcupdate.h
--- linux-2.6.24-rap/include/linux/rcupdate.h 2008-02-13 13:36:47.0
-0800
+++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-13 10:55:40.0
-0800
@@ -286,6 +286,24 @@ 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 2/2] add rcu_assign_index() if ever needed
On Thu, 14 Feb 2008 09:02:09 +0530 Gautham R Shenoy [EMAIL PROTECTED] wrote:
/**
+ * rcu_assign_index - assign (publicize) a index of a newly
+ * initialized array elementg that will be dereferenced by RCU
I hope Andrew got that one while porting against the latest -mm :)
I don't actually read the comments - I just like to make sure they're
there ;)
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