Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map
Date	2015-07-17 13:50 +0200
Message-ID	<pNcjo-4ml-7@gated-at.bofh.it> (permalink)
References	<pNbnk-31b-7@gated-at.bofh.it> <pNbnl-31b-37@gated-at.bofh.it> <pNbGG-3Dh-9@gated-at.bofh.it> <pNc02-3ZN-1@gated-at.bofh.it> <pNc9H-4aY-3@gated-at.bofh.it>
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On Fri, Jul 17, 2015 at 07:34:22PM +0800, Wangnan (F) wrote:
> On 2015/7/17 19:21, Wangnan (F) wrote:
> >On 2015/7/17 19:06, Peter Zijlstra wrote:
> >>On Fri, Jul 17, 2015 at 06:43:33PM +0800, kaixu xia wrote:
> >>>diff --git a/kernel/events/core.c b/kernel/events/core.c
> >>>index e965cfa..c4e34b7 100644
> >>>--- a/kernel/events/core.c
> >>>+++ b/kernel/events/core.c
> >>>@@ -8582,6 +8582,28 @@ void perf_event_delayed_put(struct task_struct
> >>>*task)
> >>>          WARN_ON_ONCE(task->perf_event_ctxp[ctxn]);
> >>>  }
> >>>  +struct perf_event *perf_event_get(unsigned int fd)
> >>>+{
> >>>+    struct perf_event *event;
> >>>+    struct fd f;
> >>>+
> >>>+    f = fdget(fd);
> >>>+
> >>>+    if (!f.file)
> >>>+        return ERR_PTR(-EBADF);
> >>>+
> >>>+    if (f.file->f_op != &perf_fops) {
> >>>+        fdput(f);
> >>>+        return ERR_PTR(-EINVAL);
> >>>+    }
> >>>+
> >>>+    event = f.file->private_data;
> >>>+
> >>>+    fdput(f);
> >>>+
> >>>+    return event;
> >>>+}
> >>And what is stopping userspace from closing those FDs while you're using
> >>them?

> Shall we put atomic_long_inc_not_zero() between fdget() and fdput()?

You pretty much _have_ to do that.
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Thread

[RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map kaixu xia <xiakaixu@huawei.com> - 2015-07-17 12:50 +0200
  Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map Peter Zijlstra <peterz@infradead.org> - 2015-07-17 13:10 +0200
    Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to  map "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 13:30 +0200
      Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to  map "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 13:40 +0200
        Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map Peter Zijlstra <peterz@infradead.org> - 2015-07-17 13:50 +0200
          Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to  map "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 14:00 +0200
            Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map Peter Zijlstra <peterz@infradead.org> - 2015-07-17 14:10 +0200
              Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to  map "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 14:20 +0200
  Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map Peter Zijlstra <peterz@infradead.org> - 2015-07-17 13:40 +0200

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