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[PATCH hw_breakpoint] percpu: add __percpu sparse annotations to hw_breakpoint

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Tejun Heo

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Feb 16, 2010, 8:50:02 PM2/16/10
to
Add __percpu sparse annotations to hw_breakpoint.

These annotations are to make sparse consider percpu variables to be
in a different address space and warn if accessed without going
through percpu accessors. This patch doesn't affect normal builds.

In kernel/hw_breakpoint.c, per_cpu(nr_task_bp_pinned, cpu)'s will
trigger sprious noderef related warnings from sparse. Changing it to
&per_cpu(nr_task_bp_pinned[0], cpu) will work around the problem but
deemed to ugly by the maintainer. Leave it alone until better
solution can be found.

Signed-off-by: Tejun Heo <t...@kernel.org>
Cc: Frederic Weisbecker <fwei...@gmail.com>
---
Frederic, can you please put this into the tree for hw_breakpoint?

Thanks.

include/linux/hw_breakpoint.h | 8 ++++----
kernel/hw_breakpoint.c | 10 +++++-----
samples/hw_breakpoint/data_breakpoint.c | 6 +++---
3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index 070ba06..3cf78a7 100644
--- a/include/linux/hw_breakpoint.h
+++ b/include/linux/hw_breakpoint.h
@@ -66,14 +66,14 @@ register_wide_hw_breakpoint_cpu(struct perf_event_attr *attr,
perf_overflow_handler_t triggered,
int cpu);

-extern struct perf_event **
+extern struct perf_event * __percpu *
register_wide_hw_breakpoint(struct perf_event_attr *attr,
perf_overflow_handler_t triggered);

extern int register_perf_hw_breakpoint(struct perf_event *bp);
extern int __register_perf_hw_breakpoint(struct perf_event *bp);
extern void unregister_hw_breakpoint(struct perf_event *bp);
-extern void unregister_wide_hw_breakpoint(struct perf_event **cpu_events);
+extern void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events);

extern int dbg_reserve_bp_slot(struct perf_event *bp);
extern int dbg_release_bp_slot(struct perf_event *bp);
@@ -100,7 +100,7 @@ static inline struct perf_event *
register_wide_hw_breakpoint_cpu(struct perf_event_attr *attr,
perf_overflow_handler_t triggered,
int cpu) { return NULL; }
-static inline struct perf_event **
+static inline struct perf_event * __percpu *
register_wide_hw_breakpoint(struct perf_event_attr *attr,
perf_overflow_handler_t triggered) { return NULL; }
static inline int
@@ -109,7 +109,7 @@ static inline int
__register_perf_hw_breakpoint(struct perf_event *bp) { return -ENOSYS; }
static inline void unregister_hw_breakpoint(struct perf_event *bp) { }
static inline void
-unregister_wide_hw_breakpoint(struct perf_event **cpu_events) { }
+unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events) { }
static inline int
reserve_bp_slot(struct perf_event *bp) {return -ENOSYS; }
static inline void release_bp_slot(struct perf_event *bp) { }
diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c
index 8a5c7d5..4781c68 100644
--- a/kernel/hw_breakpoint.c
+++ b/kernel/hw_breakpoint.c
@@ -413,17 +413,17 @@ EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
*
* @return a set of per_cpu pointers to perf events
*/
-struct perf_event **
+struct perf_event * __percpu *
register_wide_hw_breakpoint(struct perf_event_attr *attr,
perf_overflow_handler_t triggered)
{
- struct perf_event **cpu_events, **pevent, *bp;
+ struct perf_event * __percpu *cpu_events, **pevent, *bp;
long err;
int cpu;

cpu_events = alloc_percpu(typeof(*cpu_events));
if (!cpu_events)
- return ERR_PTR(-ENOMEM);
+ return (void __percpu __force *)ERR_PTR(-ENOMEM);

get_online_cpus();
for_each_online_cpu(cpu) {
@@ -451,7 +451,7 @@ fail:
put_online_cpus();

free_percpu(cpu_events);
- return ERR_PTR(err);
+ return (void __percpu __force *)ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);

@@ -459,7 +459,7 @@ EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
* unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
* @cpu_events: the per cpu set of events to unregister
*/
-void unregister_wide_hw_breakpoint(struct perf_event **cpu_events)
+void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
{
int cpu;
struct perf_event **pevent;
diff --git a/samples/hw_breakpoint/data_breakpoint.c b/samples/hw_breakpoint/data_breakpoint.c
index c69cbe9..bd0f337 100644
--- a/samples/hw_breakpoint/data_breakpoint.c
+++ b/samples/hw_breakpoint/data_breakpoint.c
@@ -34,7 +34,7 @@
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>

-struct perf_event **sample_hbp;
+struct perf_event * __percpu *sample_hbp;

static char ksym_name[KSYM_NAME_LEN] = "pid_max";
module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
@@ -61,8 +61,8 @@ static int __init hw_break_module_init(void)
attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;

sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
- if (IS_ERR(sample_hbp)) {
- ret = PTR_ERR(sample_hbp);
+ if (IS_ERR((void __force *)sample_hbp)) {
+ ret = PTR_ERR((void __force *)sample_hbp);
goto fail;
}

--
1.6.4.2

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Frederic Weisbecker

unread,
Feb 17, 2010, 11:50:02 AM2/17/10
to
On Wed, Feb 17, 2010 at 10:50:50AM +0900, Tejun Heo wrote:
> Add __percpu sparse annotations to hw_breakpoint.
>
> These annotations are to make sparse consider percpu variables to be
> in a different address space and warn if accessed without going
> through percpu accessors. This patch doesn't affect normal builds.
>
> In kernel/hw_breakpoint.c, per_cpu(nr_task_bp_pinned, cpu)'s will
> trigger sprious noderef related warnings from sparse. Changing it to
> &per_cpu(nr_task_bp_pinned[0], cpu) will work around the problem but
> deemed to ugly by the maintainer. Leave it alone until better
> solution can be found.
>
> Signed-off-by: Tejun Heo <t...@kernel.org>
> Cc: Frederic Weisbecker <fwei...@gmail.com>
> ---
> Frederic, can you please put this into the tree for hw_breakpoint?
>
> Thanks.


Yeah, looks good, I'm queuing it.
Just few comments below, for nano-considerations.

> cpu_events = alloc_percpu(typeof(*cpu_events));
> if (!cpu_events)
> - return ERR_PTR(-ENOMEM);
> + return (void __percpu __force *)ERR_PTR(-ENOMEM);

Is this pattern common enough that we can think about a ERR_CPU_PTR ?


> sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
> - if (IS_ERR(sample_hbp)) {
> - ret = PTR_ERR(sample_hbp);
> + if (IS_ERR((void __force *)sample_hbp)) {
> + ret = PTR_ERR((void __force *)sample_hbp);


Same comments here, although I wouldn't like much a CPU_PTR_ERR or
IS_ERR_CPU.... CPP is just so poor in magic for that.

I must confess I miss a bit the old per_cpu prefix that guarded the implicit
separate namespace.

Anyway, I'm queuing it, thanks.

Tejun Heo

unread,
Feb 17, 2010, 7:50:02 PM2/17/10
to
Hello,

On 02/18/2010 01:39 AM, Frederic Weisbecker wrote:
> On Wed, Feb 17, 2010 at 10:50:50AM +0900, Tejun Heo wrote:
> Yeah, looks good, I'm queuing it.
> Just few comments below, for nano-considerations.
>> cpu_events = alloc_percpu(typeof(*cpu_events));
>> if (!cpu_events)
>> - return ERR_PTR(-ENOMEM);
>> + return (void __percpu __force *)ERR_PTR(-ENOMEM);
>
> Is this pattern common enough that we can think about a ERR_CPU_PTR ?

I thought about that but there aren't too many yet, so I just added
the ugly castings. It would be cool if sparse can be taught that
ERR_PTR() returns universal pseudo pointer.

>> sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
>> - if (IS_ERR(sample_hbp)) {
>> - ret = PTR_ERR(sample_hbp);
>> + if (IS_ERR((void __force *)sample_hbp)) {
>> + ret = PTR_ERR((void __force *)sample_hbp);
>
> Same comments here, although I wouldn't like much a CPU_PTR_ERR or
> IS_ERR_CPU.... CPP is just so poor in magic for that.
>
> I must confess I miss a bit the old per_cpu prefix that guarded the implicit
> separate namespace.

Yeap, I agree that the prefix had its advantages. It's just that it
can't scale to the new situation where static and dynamic percpu
variables behave uniformly.

Thank you.

--
tejun

Frederic Weisbecker

unread,
Feb 18, 2010, 1:30:02 PM2/18/10
to
On Thu, Feb 18, 2010 at 09:49:08AM +0900, Tejun Heo wrote:
> Hello,
>
> On 02/18/2010 01:39 AM, Frederic Weisbecker wrote:
> > On Wed, Feb 17, 2010 at 10:50:50AM +0900, Tejun Heo wrote:
> > Yeah, looks good, I'm queuing it.
> > Just few comments below, for nano-considerations.
> >> cpu_events = alloc_percpu(typeof(*cpu_events));
> >> if (!cpu_events)
> >> - return ERR_PTR(-ENOMEM);
> >> + return (void __percpu __force *)ERR_PTR(-ENOMEM);
> >
> > Is this pattern common enough that we can think about a ERR_CPU_PTR ?
>
> I thought about that but there aren't too many yet, so I just added
> the ugly castings. It would be cool if sparse can be taught that
> ERR_PTR() returns universal pseudo pointer.

Yeah, it would be nice to just have a universal address space
that is compatible with all others. It's sad to see such
uglification to make a secondary tool happy.


> >> sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
> >> - if (IS_ERR(sample_hbp)) {
> >> - ret = PTR_ERR(sample_hbp);
> >> + if (IS_ERR((void __force *)sample_hbp)) {
> >> + ret = PTR_ERR((void __force *)sample_hbp);
> >
> > Same comments here, although I wouldn't like much a CPU_PTR_ERR or
> > IS_ERR_CPU.... CPP is just so poor in magic for that.
> >
> > I must confess I miss a bit the old per_cpu prefix that guarded the implicit
> > separate namespace.
>
> Yeap, I agree that the prefix had its advantages. It's just that it
> can't scale to the new situation where static and dynamic percpu
> variables behave uniformly.


Well, I miss a bit of per cpu internals so I won't argue further :)

Thanks.

tip-bot for Tejun Heo

unread,
Feb 28, 2010, 4:00:01 AM2/28/10
to
Commit-ID: 44ee63587dce85593c22497140db16f4e5027860
Gitweb: http://git.kernel.org/tip/44ee63587dce85593c22497140db16f4e5027860
Author: Tejun Heo <t...@kernel.org>
AuthorDate: Wed, 17 Feb 2010 10:50:50 +0900
Committer: Frederic Weisbecker <fwei...@gmail.com>
CommitDate: Sat, 27 Feb 2010 16:23:39 +0100

percpu: Add __percpu sparse annotations to hw_breakpoint

Add __percpu sparse annotations to hw_breakpoint.

These annotations are to make sparse consider percpu variables to be
in a different address space and warn if accessed without going
through percpu accessors. This patch doesn't affect normal builds.

In kernel/hw_breakpoint.c, per_cpu(nr_task_bp_pinned, cpu)'s will

trigger spurious noderef related warnings from sparse. Changing it to


&per_cpu(nr_task_bp_pinned[0], cpu) will work around the problem but
deemed to ugly by the maintainer. Leave it alone until better
solution can be found.

Signed-off-by: Tejun Heo <t...@kernel.org>
Cc: Stephen Rothwell <s...@canb.auug.org.au>
Cc: K.Prasad <pra...@linux.vnet.ibm.com>
LKML-Reference: <4B7B4B7A...@kernel.org>
Signed-off-by: Frederic Weisbecker <fwei...@gmail.com>
---


include/linux/hw_breakpoint.h | 8 ++++----
kernel/hw_breakpoint.c | 10 +++++-----
samples/hw_breakpoint/data_breakpoint.c | 6 +++---
3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index 5977b72..c70d27a 100644

index 967e661..6542eac 100644

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