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Subject[PATCH 2/2] hw-breakpoints: Fix task-bound breakpoint slot allocation
Date
Whatever the context nature of a breakpoint, we always perform the
following constraint checks before allocating it a slot:

- Check the number of pinned breakpoint bound the concerned cpus
- Check the max number of task-bound breakpoints that are belonging
to a task.
- Add both and see if we have a reamining slot for the new breakpoint

This is the right thing to do when we are about to register a cpu-only
bound breakpoint. But not if we are dealing with a task bound
breakpoint. What we want in this case is:

- Check the number of pinned breakpoint bound the concerned cpus
- Check the number of breakpoints that already belong to the task
in which the breakpoint to register is bound to.
- Add both

This fixes a regression that makes the "firefox -g" command fail to
register breakpoints once we deal with a secondary thread.

Reported-by: Walt <w41ter@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
---
kernel/hw_breakpoint.c | 74 +++++++++++++++++++++++++++++-------------------
1 files changed, 45 insertions(+), 29 deletions(-)

diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c
index b600fc2..02b4925 100644
--- a/kernel/hw_breakpoint.c
+++ b/kernel/hw_breakpoint.c
@@ -83,15 +83,51 @@ static unsigned int max_task_bp_pinned(int cpu)
return 0;
}

+static int task_bp_pinned(struct task_struct *tsk)
+{
+ struct perf_event_context *ctx = tsk->perf_event_ctxp;
+ struct list_head *list;
+ struct perf_event *bp;
+ unsigned long flags;
+ int count = 0;
+
+ if (WARN_ONCE(!ctx, "No perf context for this task"))
+ return 0;
+
+ list = &ctx->event_list;
+
+ spin_lock_irqsave(&ctx->lock, flags);
+
+ /*
+ * The current breakpoint counter is not included in the list
+ * at the open() callback time
+ */
+ list_for_each_entry(bp, list, event_entry) {
+ if (bp->attr.type == PERF_TYPE_BREAKPOINT)
+ count++;
+ }
+
+ spin_unlock_irqrestore(&ctx->lock, flags);
+
+ return count;
+}
+
/*
* Report the number of pinned/un-pinned breakpoints we have in
* a given cpu (cpu > -1) or in all of them (cpu = -1).
*/
-static void fetch_bp_busy_slots(struct bp_busy_slots *slots, int cpu)
+static void
+fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp)
{
+ int cpu = bp->cpu;
+ struct task_struct *tsk = bp->ctx->task;
+
if (cpu >= 0) {
slots->pinned = per_cpu(nr_cpu_bp_pinned, cpu);
- slots->pinned += max_task_bp_pinned(cpu);
+ if (!tsk)
+ slots->pinned += max_task_bp_pinned(cpu);
+ else
+ slots->pinned += task_bp_pinned(tsk);
slots->flexible = per_cpu(nr_bp_flexible, cpu);

return;
@@ -101,7 +137,10 @@ static void fetch_bp_busy_slots(struct bp_busy_slots *slots, int cpu)
unsigned int nr;

nr = per_cpu(nr_cpu_bp_pinned, cpu);
- nr += max_task_bp_pinned(cpu);
+ if (!tsk)
+ nr += max_task_bp_pinned(cpu);
+ else
+ nr += task_bp_pinned(tsk);

if (nr > slots->pinned)
slots->pinned = nr;
@@ -118,33 +157,10 @@ static void fetch_bp_busy_slots(struct bp_busy_slots *slots, int cpu)
*/
static void toggle_bp_task_slot(struct task_struct *tsk, int cpu, bool enable)
{
- int count = 0;
- struct perf_event *bp;
- struct perf_event_context *ctx = tsk->perf_event_ctxp;
unsigned int *tsk_pinned;
- struct list_head *list;
- unsigned long flags;
-
- if (WARN_ONCE(!ctx, "No perf context for this task"))
- return;
-
- list = &ctx->event_list;
-
- spin_lock_irqsave(&ctx->lock, flags);
-
- /*
- * The current breakpoint counter is not included in the list
- * at the open() callback time
- */
- list_for_each_entry(bp, list, event_entry) {
- if (bp->attr.type == PERF_TYPE_BREAKPOINT)
- count++;
- }
-
- spin_unlock_irqrestore(&ctx->lock, flags);
+ int count = 0;

- if (WARN_ONCE(count < 0, "No breakpoint counter found in the counter list"))
- return;
+ count = task_bp_pinned(tsk);

tsk_pinned = per_cpu(task_bp_pinned, cpu);
if (enable) {
@@ -233,7 +249,7 @@ int reserve_bp_slot(struct perf_event *bp)

mutex_lock(&nr_bp_mutex);

- fetch_bp_busy_slots(&slots, bp->cpu);
+ fetch_bp_busy_slots(&slots, bp);

/* Flexible counters need to keep at least one slot */
if (slots.pinned + (!!slots.flexible) == HBP_NUM) {
--
1.6.2.3


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