On Fri, Feb 6, 2015 at 11:49 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Fri, Feb 6, 2015 at 8:23 AM, Konstantin Khlebnikov > <khlebnikov@xxxxxxxxxxxxxx> wrote: >> Handling of flag CLONE_PARENT_SETTID has the same problem: error returned >> from put_user() is ignored. Glibc completely relies on that feature and uses >> value returned from syscall only for error checking. > > I'm not seeing the advantage of the error checking part of the pacth > patch. It generates extra code, possibly changing existing interfaces, > and it doesn't actually buy us anything. > > What's the upside? If somebody passes in a bad pointer, it's their > problem. For all we know, people used to pass in NULL, even if they > had the SETTID bit set. This makes it now return EFAULT. Currently that works fine only because kernel retries 0-order allocations endlessly. But pagefault_out_of_memory() is never called for non-user PF. For kernel PF all oom-kills are triggered by buddy-allocator. If buddy allocator gave up earlier then page-faults from kernel space could fail without OOM. And in CoW area user-space will see stale data. So, either we must handle all put_user/copy_to_user errors (which isn't that bad idea) or kernel must force all PF to success-or-die policy. First patch is that ugly because kernel has never checked errors in that place. So, I've tried to find solution which could fix problem without breaking backward compatibility. > > So I don't mind moving things into copy_process(), but I *do* mind the > new error return thing. > > It's actually better in this patch than in 1/2, because 1/2 was just > insane with the whole "readable vs writable" thing. That I refuse to > even look at, for fear of going blind. > > Linus > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
