Messages in this thread |  | | | Date | Fri, 27 Feb 2004 16:05:11 -0800 | | From | George Anzinger <> | | Subject | Re: kgdb support in vanilla 2.6.2 |
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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.
-- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml
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