Messages in this thread | | | From | "Amit S. Kale" <> | Subject | Re: kgdb support in vanilla 2.6.2 | Date | Mon, 1 Mar 2004 15:08:23 +0530 |
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On Saturday 28 Feb 2004 5:35 am, George Anzinger wrote: > Amit S. Kale wrote: > > On Friday 06 Feb 2004 6:54 pm, Andi Kleen wrote: > >>On Fri, 6 Feb 2004 18:35:16 +0530 > >> > >>"Amit S. Kale" <amitkale@emsyssoft.com> wrote: > >>>On Friday 06 Feb 2004 5:46 pm, Andi Kleen wrote: > >>>>On Fri, 6 Feb 2004 17:28:36 +0530 > >>>> > >>>>"Amit S. Kale" <amitkale@emsyssoft.com> wrote: > >>>>>On Friday 06 Feb 2004 7:50 am, Andi Kleen wrote: > >>>>>>On Thu, 5 Feb 2004 23:20:04 +0530 > >>>>>> > >>>>>>"Amit S. Kale" <amitkale@emsyssoft.com> wrote: > >>>>>>>On Thursday 05 Feb 2004 8:41 am, Andi Kleen wrote: > >>>>>>>>Andrew Morton <akpm@osdl.org> writes: > >>>>>>>>>need to take a look at such things and really convice > >>>>>>>>>ourselves that they're worthwhile. Personally, I'd only be > >>>>>>>>>interested in the basic stub. > >>>>>>>> > >>>>>>>>What I found always extremly ugly in the i386 stub was that it > >>>>>>>>uses magic globals to talk to the page fault handler. For the > >>>>>>>>x86-64 version I replaced that by just using __get/__put_user > >>>>>>>>in the memory accesses, which is much cleaner. I would suggest > >>>>>>>>doing that for i386 too. > >>>>>>> > >>>>>>>May be I am missing something obvious. When debugging a page > >>>>>>>fault handler if kgdb accesses an swapped-out user page doesn't > >>>>>>>it deadlock when trying to hold mm semaphore? > >>>>>> > >>>>>>Modern i386 kernels don't grab the mm semaphore when the access is > >>>>>> > >>>>>>>= TASK_SIZE and the access came from kernel space (actually I see > >>>>>> > >>>>>>x86-64 still does, but that's a bug, will fix). You could only see > >>>>>>a deadlock when using user addresses and you already hold the mm > >>>>>>semaphore for writing (normal read lock is ok). Just don't do that. > >>>>> > >>>>>OK. It don't deadlock when kgdb accesses kernel addresses. > >>>>> > >>>>>When a user space address is accessed through kgdb, won't the kernel > >>>>>attempt to fault in the user page? We don't want that to happen > >>>>>inside kgdb. > >>>> > >>>>Yes, it will. But I don't think it's a bad thing. If the users doesn't > >>>>want that they should not follow user addresses. After all kgdb is for > >>>>people who know what they are doing. > >>> > >>>Let kgdb refuse to access any addresses below TASK_SIZE. That's better > >>>than accidentally typing something and getting lost. > >> > >>That's fine. But can you perhaps add a magic command that enables it > >> again? > > > > Yes. This sounds good. > > This could be a flag in the kgdb_info structure. See -mm kgdb. Does not > require any new commands as it is just a global the user can change.
Having all user modifiable variables in one place is definitely a good idea. Need to do this sometime. -Amit - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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