On Fri, 17 Jan 2014 17:47:36 +0100 Borislav Petkov <[email protected]> wrote:
> On Fri, Jan 17, 2014 at 02:47:15PM +0000, Ren, Qiaowei wrote: > > > do_bounds > > > |->do_mpx_bt_fault > > > |->allocate_bt > > > |->sys_mmap_pgoff > > > |->vm_mmap_pgoff > > > |->do_mmap_pgoff > > > |->mmap_region > > > |-> kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL); > > > > > Sorry for my late reply. > > > > Petkov, could you please detail the problem? Memory allocation can't > > be done in the eception handler? I guess it is like do_page_fault(), > > right? > > Right, so Steve and I played a couple of scenarios in IRC with this. So > #BR is comparable with #PF, AFAICT, and as expected we don't take any > locks when handling page faults in kernel space as we might deadlock. > > Now, what happens if a thread is sleeping on some lock down that > GFP_KERNEL allocation path and another thread gets a #BR and goes that > same mmap_pgoff path and tries to grab that same lock? > > Also, what happens if you take a #BR in NMI context, say the NMI > handler? > > All I'm trying to say is, it might not be such a good idea to sleep in a > fault handler... > Or do what #PF does. Check if the fault happened in the kernel and go one path (probably follow what do_fault() does), otherwise if it is userspace, it's ok to sleep or grab locks or whatever you want. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
