Messages in this thread | | | Date | Tue, 24 Apr 2018 10:33:36 +0900 | From | Sergey Senozhatsky <> | Subject | Re: printk feature for syzbot? |
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Let me Cc Petr, Steven and Fengguang on this
On (04/23/18 15:40), Dmitry Vyukov wrote: > On Mon, Apr 23, 2018 at 3:33 PM, Tetsuo Handa > <penguin-kernel@i-love.sakura.ne.jp> wrote: > > Hello, Sergey. > > > > Recently I'm fixing bugs reported by syzbot ( https://syzkaller.appspot.com/ ). > > > > Since syzbot frequently makes printk() flooding (e.g. memory allocation fault > > injection), it is always difficult to distinguish which line is from which event. > > > > I wish printk() can prefix context identifier. > > If I recall correctly, you are using some extra output for debugging, aren't you? > > +syzkaller mailing list for history > > Hi Tetsuo, Sergey, > > Something like TID prefix would be useful. Potentially it would allow > us to untangle multiple intermixed crash reports.
Hello,
Yes, Tetsuo, we use a bunch of "printk prefix" extensions at Samsung. For instance, we prefix printk messages with the CPU number: messages sometimes mix up, we also see partial pr_cont flushes, and so on. Grep-ping serial logs by CPU number is quite powerful.
Upstreaming those printk prefixes can be a bit challenging, but may be it's not all so bad. I personally think that syzbot, and build-test bots in general [like 0day], are helpful indeed, and I don't see why life should be any more complex for syzbot/0day guys. If printk prefixes can help - then we probably should consider such an extension.
The main argument from the upstream is that tweaking struct printk_log breaks user space (tools like crash, and so on). But I guess we can do something about it. E.g. put a PRINTK_CONTEXT_TRACKING_PREFIX kconfig option somewhere in "Kernel hacking"->"printk and dmesg options" and make available only for DEBUG kernels, or something similar.
Petr, Steven, Fengguang, what do you think? Do you have any objections? Ideas?
-ss
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