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Date: Mon, 4 Apr 2011 15:02:08 +0200 From: Robert Święcki <robert@...ecki.net> To: Hui Zhu <teawater@...il.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Hugh Dickins <hughd@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Miklos Szeredi <miklos@...redi.hu>, Michel Lespinasse <walken@...gle.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Rik van Riel <riel@...hat.com> Subject: Re: [PATCH] mm: fix possible cause of a page_mapped BUG On Sat, Apr 2, 2011 at 6:01 AM, Hui Zhu <teawater@...il.com> wrote: > On Sat, Apr 2, 2011 at 00:35, Linus Torvalds > <torvalds@...ux-foundation.org> wrote: >> On Fri, Apr 1, 2011 at 9:21 AM, Robert Święcki <robert@...ecki.net> wrote: >>> >>> Is it possible to turn it off via config flags? Looking into >>> arch/x86/include/asm/bug.h it seems it's unconditional (as in "it >>> always manifests itself somehow") and I have >>> CONFIG_DEBUG_BUGVERBOSE=y. >> >> Ok, if you have CONFIG_DEBUG_BUGVERBOSE then, you do have the bug-table. >> >> Maybe it's just kdb that is broken, and doesn't print it. I wouldn't >> be surprised. It's not the first time I've seen debugging features >> that just make debugging a mess. >> >>> Anything that could help you debugging this? Uploading kernel image >>> (unfortunately I've overwritten this one), dumping more kgdb data? >> >> So in this case kgdb just dropped the most important data on the floor. >> >> But if you have kdb active next time, print out the vma/old contents >> in that function that has the BUG() in it. >> >>> I must admit I'm not up-to-date with current linux kernel debugging >>> techniques. The kernel config is here: >>> http://alt.swiecki.net/linux_kernel/ise-test-2.6.38-kernel-config.txt >>> >>> For now I'll compile with -O0 -fno-inline (are you sure you'd like -Os?) > > Hi Robert, > > I am not sure you can success with build trunk with -O0 -fno-inline. > I suggest you try the patch in > http://code.google.com/p/kgtp/downloads/detail?name=co.patch. > It add a option in "Kernel hacking" called "Compile with almost no > optimization". It will make kernel be built without -O2. It support > x86_32, x86_64 and arm. HI, Yeah.. -O0 doesn't build smoothly, it seems that building with -O0 is not required right now, but I'll keep your patch in mind in case it becomes necessary. Thanks for the tip. > PS, maybe you can try kgtp (https://code.google.com/p/kgtp/) debug your kernel. > >> >> Oh, don't do that. -O0 makes the code totally unreadable (the compiler >> just does _stupid_ things, making the asm code look so horrible that >> you can't match it up against anything sane), and -fno-inline isn't >> worth the pain either. >> >> -Os is much better than those. >> >> But in this case, just getting the filename and line number would have >> made the thing moot anyway - without kdb it _should_ have said >> something clear like >> >> kernel BUG at %s:%u! >> >> where %s:%u is the filename and line number. >> >> Linus >> -- >> 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/ >> > -- Robert Święcki -- 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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