* [PATCH] events: Reuse value read using READ_ONCE instead of re-reading it
@ 2021-09-06 1:53 Baptiste Lepers
2021-09-10 16:21 ` Peter Zijlstra
0 siblings, 1 reply; 2+ messages in thread
From: Baptiste Lepers @ 2021-09-06 1:53 UTC (permalink / raw)
Cc: Baptiste Lepers, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Mark Rutland, Alexander Shishkin,
Jiri Olsa, Namhyung Kim, Mathieu Poirier, linux-perf-users,
linux-kernel
In perf_event_addr_filters_apply, the task associated with
the event (event->ctx->task) is read using READ_ONCE at the beginning
of the function, checked, and then re-read from event->ctx->task,
voiding all guarantees of the checks. Reuse the value that was read by
READ_ONCE to ensure the consistency of the task struct throughout the
function.
Signed-off-by: Baptiste Lepers <baptiste.lepers@gmail.com>
Fixes: 375637bc52495 ("perf/core: Introduce address range filtering")
---
kernel/events/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 744e8726c5b2..0c000cb01eeb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10193,7 +10193,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)
return;
if (ifh->nr_file_filters) {
- mm = get_task_mm(event->ctx->task);
+ mm = get_task_mm(task);
if (!mm)
goto restart;
--
2.17.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] events: Reuse value read using READ_ONCE instead of re-reading it
2021-09-06 1:53 [PATCH] events: Reuse value read using READ_ONCE instead of re-reading it Baptiste Lepers
@ 2021-09-10 16:21 ` Peter Zijlstra
0 siblings, 0 replies; 2+ messages in thread
From: Peter Zijlstra @ 2021-09-10 16:21 UTC (permalink / raw)
To: Baptiste Lepers
Cc: Ingo Molnar, Arnaldo Carvalho de Melo, Mark Rutland,
Alexander Shishkin, Jiri Olsa, Namhyung Kim, Mathieu Poirier,
linux-perf-users, linux-kernel
On Mon, Sep 06, 2021 at 11:53:10AM +1000, Baptiste Lepers wrote:
> In perf_event_addr_filters_apply, the task associated with
> the event (event->ctx->task) is read using READ_ONCE at the beginning
> of the function, checked, and then re-read from event->ctx->task,
> voiding all guarantees of the checks. Reuse the value that was read by
> READ_ONCE to ensure the consistency of the task struct throughout the
> function.
>
> Signed-off-by: Baptiste Lepers <baptiste.lepers@gmail.com>
> Fixes: 375637bc52495 ("perf/core: Introduce address range filtering")
Thanks!
^ permalink raw reply [flat|nested] 2+ messages in thread
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