Commit-ID: dddd3379a619a4cb8247bfd3c94ca9ae3797aa2e
Gitweb: http://git.kernel.org/tip/dddd3379a619a4cb8247bfd3c94ca9ae3797aa2e
Author: Thomas Gleixner <[email protected]>
AuthorDate: Wed, 24 Nov 2010 10:05:55 +0100
Committer: Ingo Molnar <[email protected]>
CommitDate: Fri, 26 Nov 2010 15:00:56 +0100
perf: Fix inherit vs. context rotation bug
It was found that sometimes children of tasks with inherited events had
one extra event. Eventually it turned out to be due to the list rotation
no being exclusive with the list iteration in the inheritance code.
Cure this by temporarily disabling the rotation while we inherit the events.
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
LKML-Reference: <new-submission>
Cc: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
---
include/linux/perf_event.h | 1 +
kernel/perf_event.c | 22 ++++++++++++++++++++--
2 files changed, 21 insertions(+), 2 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 40150f3..142e3d6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -850,6 +850,7 @@ struct perf_event_context {
int nr_active;
int is_active;
int nr_stat;
+ int rotate_disable;
atomic_t refcount;
struct task_struct *task;
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 671f6c8..f365dd8 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1622,8 +1622,12 @@ static void rotate_ctx(struct perf_event_context *ctx)
{
raw_spin_lock(&ctx->lock);
- /* Rotate the first entry last of non-pinned groups */
- list_rotate_left(&ctx->flexible_groups);
+ /*
+ * Rotate the first entry last of non-pinned groups. Rotation might be
+ * disabled by the inheritance code.
+ */
+ if (!ctx->rotate_disable)
+ list_rotate_left(&ctx->flexible_groups);
raw_spin_unlock(&ctx->lock);
}
@@ -6162,6 +6166,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
struct perf_event *event;
struct task_struct *parent = current;
int inherited_all = 1;
+ unsigned long flags;
int ret = 0;
child->perf_event_ctxp[ctxn] = NULL;
@@ -6202,6 +6207,15 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
break;
}
+ /*
+ * We can't hold ctx->lock when iterating the ->flexible_group list due
+ * to allocations, but we need to prevent rotation because
+ * rotate_ctx() will change the list from interrupt context.
+ */
+ raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+ parent_ctx->rotate_disable = 1;
+ raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
ret = inherit_task_group(event, parent, parent_ctx,
child, ctxn, &inherited_all);
@@ -6209,6 +6223,10 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
break;
}
+ raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+ parent_ctx->rotate_disable = 0;
+ raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
child_ctx = child->perf_event_ctxp[ctxn];
if (child_ctx && inherited_all) {
On Fri, Nov 26, 2010 at 9:00 PM, tip-bot for Thomas Gleixner
<[email protected]> wrote:
> Commit-ID: ?dddd3379a619a4cb8247bfd3c94ca9ae3797aa2e
> Gitweb: ? ? http://git.kernel.org/tip/dddd3379a619a4cb8247bfd3c94ca9ae3797aa2e
> Author: ? ? Thomas Gleixner <[email protected]>
> AuthorDate: Wed, 24 Nov 2010 10:05:55 +0100
> Committer: ?Ingo Molnar <[email protected]>
> CommitDate: Fri, 26 Nov 2010 15:00:56 +0100
>
> perf: Fix inherit vs. context rotation bug
>
> It was found that sometimes children of tasks with inherited events had
> one extra event. Eventually it turned out to be due to the list rotation
> no being exclusive with the list iteration in the inheritance code.
>
> Cure this by temporarily disabling the rotation while we inherit the events.
>
> Signed-off-by: Thomas Gleixner <[email protected]>
> Signed-off-by: Peter Zijlstra <[email protected]>
> LKML-Reference: <new-submission>
> Cc: <[email protected]>
> Signed-off-by: Ingo Molnar <[email protected]>
> ---
> ?include/linux/perf_event.h | ? ?1 +
> ?kernel/perf_event.c ? ? ? ?| ? 22 ++++++++++++++++++++--
> ?2 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 40150f3..142e3d6 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -850,6 +850,7 @@ struct perf_event_context {
> ? ? ? ?int ? ? ? ? ? ? ? ? ? ? ? ? ? ? nr_active;
> ? ? ? ?int ? ? ? ? ? ? ? ? ? ? ? ? ? ? is_active;
> ? ? ? ?int ? ? ? ? ? ? ? ? ? ? ? ? ? ? nr_stat;
> + ? ? ? int ? ? ? ? ? ? ? ? ? ? ? ? ? ? rotate_disable;
Isn't it convincing to use atomic_t instead of int as rotate_disable
type. Since, we just have to increment or decrement it inside
raw_spin_lock_irqsave(), we could've easily do it using
atomic_inc/atomic_dec and atomic_read while calling
list_rotate_left(). It will allow us to remove raw_spin_lock_irqsave()
at increment/decrement. Am I missing anyting?
thanks,
rakib
> ? ? ? ?atomic_t ? ? ? ? ? ? ? ? ? ? ? ?refcount;
> ? ? ? ?struct task_struct ? ? ? ? ? ? ?*task;
>
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index 671f6c8..f365dd8 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -1622,8 +1622,12 @@ static void rotate_ctx(struct perf_event_context *ctx)
> ?{
> ? ? ? ?raw_spin_lock(&ctx->lock);
>
> - ? ? ? /* Rotate the first entry last of non-pinned groups */
> - ? ? ? list_rotate_left(&ctx->flexible_groups);
> + ? ? ? /*
> + ? ? ? ?* Rotate the first entry last of non-pinned groups. Rotation might be
> + ? ? ? ?* disabled by the inheritance code.
> + ? ? ? ?*/
> + ? ? ? if (!ctx->rotate_disable)
> + ? ? ? ? ? ? ? list_rotate_left(&ctx->flexible_groups);
>
> ? ? ? ?raw_spin_unlock(&ctx->lock);
> ?}
> @@ -6162,6 +6166,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
> ? ? ? ?struct perf_event *event;
> ? ? ? ?struct task_struct *parent = current;
> ? ? ? ?int inherited_all = 1;
> + ? ? ? unsigned long flags;
> ? ? ? ?int ret = 0;
>
> ? ? ? ?child->perf_event_ctxp[ctxn] = NULL;
> @@ -6202,6 +6207,15 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
> ? ? ? ? ? ? ? ? ? ? ? ?break;
> ? ? ? ?}
>
> + ? ? ? /*
> + ? ? ? ?* We can't hold ctx->lock when iterating the ->flexible_group list due
> + ? ? ? ?* to allocations, but we need to prevent rotation because
> + ? ? ? ?* rotate_ctx() will change the list from interrupt context.
> + ? ? ? ?*/
> + ? ? ? raw_spin_lock_irqsave(&parent_ctx->lock, flags);
> + ? ? ? parent_ctx->rotate_disable = 1;
> + ? ? ? raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
> +
> ? ? ? ?list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
> ? ? ? ? ? ? ? ?ret = inherit_task_group(event, parent, parent_ctx,
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? child, ctxn, &inherited_all);
> @@ -6209,6 +6223,10 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
> ? ? ? ? ? ? ? ? ? ? ? ?break;
> ? ? ? ?}
>
> + ? ? ? raw_spin_lock_irqsave(&parent_ctx->lock, flags);
> + ? ? ? parent_ctx->rotate_disable = 0;
> + ? ? ? raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
> +
> ? ? ? ?child_ctx = child->perf_event_ctxp[ctxn];
>
> ? ? ? ?if (child_ctx && inherited_all) {
> --
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