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Subject[PATCH 1/3] hw_breakpoint: Simplify list/idx mess in toggle_bp_slot() paths
The enable/disable logic in toggle_bp_slot() is not symmetrical
and imho very confusing. "old_count" in toggle_bp_task_slot() is
actually new_count because this bp was already removed from the
list.

Change toggle_bp_slot() to always call list_add/list_del after
toggle_bp_task_slot(). This way old_idx is task_bp_pinned() and
this entry should be decremented, new_idx is +/-weight and we
need to increment this element. The code/logic looks obvious.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/events/hw_breakpoint.c | 40 ++++++++++++++++------------------------
1 files changed, 16 insertions(+), 24 deletions(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index ed31fe1..21a3c88 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -185,26 +185,20 @@ fetch_this_slot(struct bp_busy_slots *slots, int weight)
static void toggle_bp_task_slot(struct perf_event *bp, int cpu, bool enable,
enum bp_type_idx type, int weight)
{
- unsigned int *tsk_pinned;
- int old_count = 0;
- int old_idx = 0;
- int idx = 0;
-
- old_count = task_bp_pinned(cpu, bp, type);
- old_idx = old_count - 1;
- idx = old_idx + weight;
-
- /* tsk_pinned[n] is the number of tasks having n breakpoints */
- tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
- if (enable) {
- tsk_pinned[idx]++;
- if (old_count > 0)
- tsk_pinned[old_idx]--;
- } else {
- tsk_pinned[idx]--;
- if (old_count > 0)
- tsk_pinned[old_idx]++;
- }
+ /* tsk_pinned[n-1] is the number of tasks having n>0 breakpoints */
+ unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
+ int old_idx, new_idx;
+
+ old_idx = task_bp_pinned(cpu, bp, type) - 1;
+ if (enable)
+ new_idx = old_idx + weight;
+ else
+ new_idx = old_idx - weight;
+
+ if (old_idx >= 0)
+ tsk_pinned[old_idx]--;
+ if (new_idx >= 0)
+ tsk_pinned[new_idx]++;
}

/*
@@ -228,10 +222,6 @@ toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
}

/* Pinned counter task profiling */
-
- if (!enable)
- list_del(&bp->hw.bp_list);
-
if (cpu >= 0) {
toggle_bp_task_slot(bp, cpu, enable, type, weight);
} else {
@@ -241,6 +231,8 @@ toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,

if (enable)
list_add_tail(&bp->hw.bp_list, &bp_task_head);
+ else
+ list_del(&bp->hw.bp_list);
}

/*
--
1.5.5.1



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