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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. -Amit > I could imagine in a few cases it will be useful because there may be pages > mapped into the user address space that are not in the direct mapping > (that's mainly on 32bit of course, on amd64 you can always access all > memory using mappings >TASK_SIZE) > > -Andi - 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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