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Subject[PATCH 1/3 v2] perf_event: fix race in perf_swevent_get_recursion_context()
It only disable preemption in perf_swevent_get_recursion_context(),
it can't avoid race of hard-irq and NMI since they are nested that
will re-enter this path and make the recursion value chaotic

In this patch, we use atomic operation to avoid it and reduce
cpu_ctx->recursion size, it also make this patch no need disable
preemption

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
include/linux/perf_event.h | 2 +-
kernel/perf_event.c | 14 ++++----------
2 files changed, 5 insertions(+), 11 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c6f812e..8474ab0 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -730,7 +730,7 @@ struct perf_cpu_context {
*
* task, softirq, irq, nmi context
*/
- int recursion[4];
+ unsigned long recursion;
};

struct perf_output_handle {
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index eae6ff6..77ef16e 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3921,7 +3921,7 @@ static void perf_swevent_ctx_event(struct perf_event_context *ctx,

int perf_swevent_get_recursion_context(void)
{
- struct perf_cpu_context *cpuctx = &get_cpu_var(perf_cpu_context);
+ struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
int rctx;

if (in_nmi())
@@ -3933,13 +3933,8 @@ int perf_swevent_get_recursion_context(void)
else
rctx = 0;

- if (cpuctx->recursion[rctx]) {
- put_cpu_var(perf_cpu_context);
+ if (test_and_set_bit(rctx, &cpuctx->recursion))
return -1;
- }
-
- cpuctx->recursion[rctx]++;
- barrier();

return rctx;
}
@@ -3948,9 +3943,8 @@ EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context);
void perf_swevent_put_recursion_context(int rctx)
{
struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
- barrier();
- cpuctx->recursion[rctx]--;
- put_cpu_var(perf_cpu_context);
+
+ clear_bit(rctx, &cpuctx->recursion);
}
EXPORT_SYMBOL_GPL(perf_swevent_put_recursion_context);

--
1.6.1.2



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