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Date: Mon, 26 Oct 2009 17:13:27 +0200 From: "Shargorodsky Atal (EXT-Teleca/Helsinki)" <ext-atal.shargorodsky@...ia.com> To: ext Simon Kagstrom <simon.kagstrom@...insight.net> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...e.hu>, Artem Bityutskiy <dedekind1@...il.com>, linux-mtd <linux-mtd@...ts.infradead.org>, David Woodhouse <dwmw2@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, "Koskinen Aaro (Nokia-D/Helsinki)" <aaro.koskinen@...ia.com>, Alan Cox <alan@...rguk.ukuu.org.uk> Subject: Re: [PATCH v11 4/5] core: Add kernel message dumper to call on oopses and panics On Mon, 2009-10-26 at 12:53 +0100, ext Simon Kagstrom wrote: > On Mon, 26 Oct 2009 12:36:33 +0200 > "Shargorodsky Atal (EXT-Teleca/Helsinki)" <ext-atal.shargorodsky@...ia.com> wrote: > > > > > I can think of a couple of way to figure it out in the module > > > > itself, but I could not think of any clean way to do it. > > > > > > This is correct, and the mtdoops driver has some provisions to handle > > > this. First, there is a parameter to the module to specify whether > > > oopses should be dumped at all - I added this for the particular case > > > that someone has panic_on_oops set. > > > > It takes care of most of the situations, but panic_on_oops > > can be changed any time, even after the module is loaded. > > Yes, but this parameter is settable at runtime as well by writing > to /sys/module/mtdoops/parameters/dump_oops. > > > > Second, it does not dump oopses directly anyway, but puts it in a work > > > queue. That way, if panic_on_oops is set, it will store the panic but > > > the oops (called from the workqueue) will not get written anyway. > > > > > > > AFAIK, mtdoops does not put oopses in a work queue. And if by any chance > > it does, then I think it's wrong and might lead to missed oopses, as > > the oops might be because of the work queues themselves, or it might > > look to the kernel like some non-fatal fault, but actually it's a > > sign of a much more catastrophic failure - IOMMU device garbaging > > memory, for instance. > > I was referring to my patches to it, sorry. It's in the patch "[PATCH v7 5/5]: > mtdoops: refactor as a kmsg_dumper" (as well as the parameter to dump > oopses at all). > > There are other situations which will make dumping problematic as well, > e.g., crashes in the mtd code, so there are certainly some cases which > will be difficult to catch. But in the panic_on_oops case or > oops-in-interrupt, the oops won't be missed and won't be outputted > twice for mtdoops. > > > Anyway, I understand your problem and agree that it would be good to > fix. Moving up crash_kexec() and the notifiers will at least fix your > second issue. For the double-output-of-oopses, I don't see a good way > to fix it unless relying on the module to correct it like above. > How about adding KMSG_DUMP_LAST_OOPS_BEFORE_PANIC or something to the kmsg_dump_reason enum, and making the kmsg_dump look like kmsg_dump(panic_on_oops ? KMSG_DUMP_LAST_OOPS_BEFORE_PANIC : KMSG_DUMP_OOPS); in oops_exit. Then let the dumpers decide what they want to do about it. Just a thought. And since you have no objections about moving notifiers up, it looks like the second issue will be resolved, I believe Artem will take care of it. :) Thanks a lot, Atal. > // Simon -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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