Date: Mon, 29 Mar 2010 22:18:35 +0200 From: "C. P. Ghost" <cpghost@cordula.ws> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-stable@freebsd.org Subject: Re: random FreeBSD panics Message-ID: <d74eb87c1003291318q334a9130p4e5f46dfb123611@mail.gmail.com> In-Reply-To: <201003291427.34641.jhb@freebsd.org> References: <b10011eb1003280128k4034e667v1377205888e7a2d@mail.gmail.com> <b10011eb1003291001u767b860aybfc95286d6b04ea6@mail.gmail.com> <20100329173038.GA4969@icarus.home.lan> <201003291427.34641.jhb@freebsd.org>
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On Mon, Mar 29, 2010 at 8:27 PM, John Baldwin <jhb@freebsd.org> wrote: >> To developers: what incentives would help get this issue well-needed >> attention? This problem makes kernel debugging, panic analysis, and >> other console-oriented viewing basically impossible. > > I was recently going to look at it. The somewhat drastic approach I was going > to take was to add a simple serializing lock around trap_fatal() and a few > other places that do similar block prints (e.g. mca_log()). One of the issues > with fixing this in printf itself is that you'd want probably want to > serialize complete lines of text on a per-thread basis. You would want to be > able to accumulate this line of text across multiple calls to printf (think of > it as line-buffering ala stdio). However, some folks may be nervous about > printf not printing things immediately. > > The other issue is that lots of code assumes it can call printf from anywhere > and everywhere. Mostly this just means that if you add locking and line- > buffering to printf(9) you have to be very careful to make sure it works in > odd places. Probably a lot of this could be solved by deferring things like > trap_fatal() until panic() has already been called (which is bde's preferred > solution I think). How about serializing all printf(9) through a dedicated kernel thread? Maybe something as flexible as syslogd for kernel space (klogd), that could also redirect output to a file, to a serial console etc...? > John Baldwin -cpghost. -- Cordula's Web. http://www.cordula.ws/
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