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trace: reenable preemption if we modify the ip 

Things got moved around between the original bpf_override_return patches
and the final version, and now the ftrace kprobe dispatcher assumes if
you modified the ip that you also enabled preemption.  Make a comment of
this and enable preemption, this fixes the lockdep splat that happened
when using this feature.

Fixes: 9802d86585 ("bpf: add a bpf_override_function helper")
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Josef Bacik 2017-12-15 21:42:57 -05:00 committed by Daniel Borkmann
parent 4a29c0db69
commit 46df3d209d
1 changed files with 8 additions and 1 deletions
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9
kernel/trace/trace_kprobe.c
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@ -1322,8 +1322,15 @@ static int kprobe_dispatcher(struct kprobe *kp, struct pt_regs *regs)
if (tk->tp.flags & TP_FLAG_TRACE)
kprobe_trace_func(tk, regs);
#ifdef CONFIG_PERF_EVENTS
if (tk->tp.flags & TP_FLAG_PROFILE)
if (tk->tp.flags & TP_FLAG_PROFILE) {
ret = kprobe_perf_func(tk, regs);
/*
* The ftrace kprobe handler leaves it up to us to re-enable
* preemption here before returning if we've modified the ip.
*/
if (ret)
preempt_enable_no_resched();
}
#endif
return ret;
}