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From: Alexei Starovoitov <ast@fb.com>
To: Stanislav Fomichev <sdf@fomichev.me>, Yonghong Song <yhs@fb.com>
Cc: "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <Kernel-team@fb.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH bpf-next v2 0/3] bpf: implement bpf_send_signal() helper
Date: Wed, 22 May 2019 16:43:09 +0000
Message-ID: <01865520-1963-9acd-b404-8eac03905baf@fb.com> (raw)
In-Reply-To: <20190522163854.GJ10244@mini-arch>

On 5/22/19 9:38 AM, Stanislav Fomichev wrote:
> On 05/21, Yonghong Song wrote:
>> This patch tries to solve the following specific use case.
>>
>> Currently, bpf program can already collect stack traces
>> through kernel function get_perf_callchain()
>> when certain events happens (e.g., cache miss counter or
>> cpu clock counter overflows). But such stack traces are
>> not enough for jitted programs, e.g., hhvm (jited php).
>> To get real stack trace, jit engine internal data structures
>> need to be traversed in order to get the real user functions.
>>
>> bpf program itself may not be the best place to traverse
>> the jit engine as the traversing logic could be complex and
>> it is not a stable interface either.
>>
>> Instead, hhvm implements a signal handler,
>> e.g. for SIGALARM, and a set of program locations which
>> it can dump stack traces. When it receives a signal, it will
>> dump the stack in next such program location.
>>
> 
> [..]
>> This patch implements bpf_send_signal() helper to send
>> a signal to hhvm in real time, resulting in intended stack traces.
> Series looks good. One minor nit/question: maybe rename bpf_send_signal
> to something like bpf_send_signal_to_current/bpf_current_send_signal/etc?
> bpf_send_signal is too generic now that you send the signal
> to the current process..

bpf_send_signal_to_current was Yonghong's original name
and I asked him to rename it to bpf_send_signal :)
I don't see bpf sending signals to arbitrary processes
in the near future.

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-22  5:39 Yonghong Song
2019-05-22  5:39 ` [PATCH bpf-next v2 1/3] " Yonghong Song
2019-05-23 15:41   ` Daniel Borkmann
2019-05-23 15:58     ` Yonghong Song
2019-05-23 16:28       ` Daniel Borkmann
2019-05-23 21:07         ` Yonghong Song
2019-05-23 21:30           ` Yonghong Song
2019-05-23 23:08             ` Daniel Borkmann
2019-05-23 23:54               ` Yonghong Song
2019-05-24 21:32                 ` Daniel Borkmann
2019-05-22  5:39 ` [PATCH bpf-next v2 2/3] tools/bpf: sync bpf uapi header bpf.h to tools directory Yonghong Song
2019-05-22  5:39 ` [PATCH bpf-next v2 3/3] tools/bpf: add a selftest for bpf_send_signal() helper Yonghong Song
2019-05-22 18:48   ` Andrii Nakryiko
2019-05-22 19:38     ` Yonghong Song
2019-05-22 19:10   ` Stanislav Fomichev
2019-05-22 19:44     ` Yonghong Song
2019-05-22 16:38 ` [PATCH bpf-next v2 0/3] bpf: implement " Stanislav Fomichev
2019-05-22 16:43   ` Alexei Starovoitov [this message]
2019-05-22 17:11     ` Stanislav Fomichev

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