Messages in this thread | | | Date | Mon, 12 Oct 2009 15:39:37 +0200 | From | Simon Kagstrom <> | Subject | Re: [PATCH] panic.c: export panic_on_oops |
| |
OK, I don't think we understand each other. Sorry if I'm being slow here, please tell me if I'm misunderstanding something fundamental below.
On Mon, 12 Oct 2009 15:15:29 +0200 Ingo Molnar <mingo@elte.hu> wrote:
> > I'm afraid I don't really see this issue. The workqueue is used to > > write the buffer to the mtd device if we are not in a panic or > > interrupt context - in which case we do it directly. > > > > So it's only used when an oops is ongoing. > > This fixation on 'panic' is so wrong! > > 90% of the bugs users care about dont involve any panic. And even if > there is a panic down the line, most of the interesting messages are in > the stream leading up to the panic - now tucked away in that async > workqueue mechanism and not visible.
Well, this is what my patch [1] aims to fix. What it does is to put all messages in a circular buffer, and when an oops or panic occurs it writes them out. The current version only collects messages _during_ an oops. I'll rework it with using kfifo as per Alans suggestion though.
Neither the current code nor the new patch has them stored in the work queue during a panic though. If this happens, they will call panic_write (if it's available) to write it out directly.
> There's two clean solutions i think: > > 1) add some new "ok, there's trouble!" callback to struct console and > the console driver could via that mechanism send out the _last_ 2KB > (or more) of kernel log messages. Basically we can go back in time by > looking at the dmesg buffer. The low level console driver does not > need to 'follow' the high level console state - it only wants to > print in case of trouble anyway. > > 2) or add buffered (flash-friendly) writes for all printk output - panic > and non-panic alike. This would be useful to debug suspend/resume > bugs for example. This would also optimize the packets of netconsole > output. (last i checked we sent a packet per line.)
Well, suspend/resume hangs is one of the cases which mtdoops won't catch. But at least on NAND flash, I'd be a bit weary about logging all printk output for fear of wearing out the flash.
> The workqueue looks wrong in both variants. If we are panic-ing (or > hanging, or ...) then we are halting the machine - the workqueue has no > chance to actually execute.
but then we are using mtd->panic_write to write it out directly, not via the work queue.
// Simon
[1] http://patchwork.ozlabs.org/patch/35750/
| |