On 09 Aug 2006 05:09:11 +0200 Andi Kleen <[EMAIL PROTECTED]> wrote: > Kirill Korotaev <[EMAIL PROTECTED]> writes: > > [adding linux-arch] > > > > Accessing freed memory is a bug, always, not just *only* when slab > > > debugging is on, right? Doesn't this mean we could get junk, or that > > > the reader could potentially run off a bad pointer? > > no, read the comment in sys_getppid. > > It is a valid optimization. _safe_ and alowing to bypass taking the lock. > > BUT! This optimization relies on the fact that kernel memory (DMA + normal > > zone) > > is always mapped into virtual address space. > > Which is invalid for debug kernels only. > > In x86 arch code we would use __get_user for this (and we do in a couple > of places). But it wouldn't be portable because sometimes _user is > in a different address space. > > Maybe it would be time to make a similar facility (read/write_kernel_safe() > or similar) > with error return available to generic code? > > It should be easy to implement - iirc near all architectures already > use the exception handling frame work and it is a simple extension > of that. x86 could just define it to __put/get_user >
I just did something like that: Similar to ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.18-rc3/2.6.18-rc3-mm2/broken-out/add-probe_kernel_address.patch Although I'm not sure it's needed for this problem. A getppid() which does asmlinkage long sys_getppid(void) { int pid; read_lock(&tasklist_lock); pid = current->group_leader->real_parent->tgid; read_unlock(&tasklist_lock); return pid; } seems like a fine implementation to me ;) - To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
