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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.

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20130620155011.GA6330@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Oleg Nesterov 2013-06-20 17:50:11 +02:00 committed by Ingo Molnar
parent f070a4dba9
commit e1ebe86203
1 changed files with 14 additions and 22 deletions
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36
kernel/events/hw_breakpoint.c
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@ -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;
/* 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_count = task_bp_pinned(cpu, bp, type);
old_idx = old_count - 1;
idx = old_idx + weight;
old_idx = task_bp_pinned(cpu, bp, type) - 1;
if (enable)
new_idx = old_idx + weight;
else
new_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]++;
}
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);
}
/*