On Wed, 27 Feb 2008, David Miller wrote: > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Date: Wed, 27 Feb 2008 09:02:22 +0100 (CET) > > > On Tue, 26 Feb 2008, David Miller wrote: > > > What the FUTEX checking code is doing now is doing a "user" access > > > with set_fs(KERNEL_DS) since it runs from the kernel bootup early init > > > sequence. And this is illegal according to the existing checks. > > > > > > When we do set_fs(KERNEL_DS) then pass a "user" pointer down > > > into a system call or something like that, we give it a pointer > > > that "cannot fault". So if we get into the fault handling > > > path here for a case like that we really do want to scream and > > > print out an OOPS message in my opinion. > > > > So it would be correct to set_fs(USER_DS) then do the check and switch > > back to KERNEL_DS ? > > No, I'm saying it would be better not to take faults purposefully in > the kernel address space. I would have preferred not to. The hassle is that we need to figure out, whether it works or not _before_ any user space program can use the interfaces. We could omit the check for archs where the in_atomic_cmpxchg is guaranteed to be functional. > We don't have a usable user address space > setup at this point in the boot, so using USER_DS would be even worse. Ouch, yes. Stupid me. > I think I'll just add a different version of the sanity check to this > sparc64 code later on, one that will take into consideration this > KERNEL_DS case because I can see how it could be useful in other > circumstances. Ok. Thanks, tglx - To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
