On Thu, Mar 30, 2017 at 8:28 AM, Oleg Nesterov <[email protected]> wrote: > On 03/29, Andy Lutomirski wrote: >> >> On Wed, Mar 29, 2017 at 8:05 AM, Oleg Nesterov <[email protected]> wrote: >> > On 03/28, Oleg Nesterov wrote: >> >> >> >> On 03/28, Andy Lutomirski wrote: >> >> > >> >> > How about we store the syscall arch to be restored in task_struct >> >> > along with restart_block? >> >> >> >> Yes, perhaps we will have to finally do this. Not really nice too. >> > >> > OK, how about the hack below? >> > >> > I do not want to a new member into task_struct/restart_block, so the >> > patch below adds a sticky TS_COMPAT bit which logically is a member >> > of "struct restart_block". >> >> Okay, but I'd much rather we just added a helper that's called in the >> few places that actually write to restart_block. > > Oh, yes, I thought about this too. This obviously needs more changes, and > every arch needs a dummy definition... I was thinking about > > static inline long setup_restart_block(void) > { > if (TS_COMPAT) > set TS_COMPAT_XXX; > else > clear TS_COMPAT_XXX; > > return -ERESTART_RESTARTBLOCK; > } > > so that we can do > > - ret = -ERESTART_RESTARTBLOCK; > + ret = setup_restart_block(); > > but I don't really like this... Do you strongly prefer it over the > -ERESTART_RESTARTBLOCK check in syscall_return_slowpath? I agree it doesn't > look nice too but it connects to other TS_ magic we do in arch/x86/entry/, > perhaps it is not that bad...
How about: struct restart_block *restart = set_syscall_restart_fn(do_whatever); restart->other_stuff = blah. I'd rather avoid adding stuff to the slow path that runs *that* rarely. > >> Or we just add the new syscall nr and see what breaks. The answer >> could well be nothing at all. > > Well, strace knows about __NR_restart_syscall. It won't be really broken, > but I guess it will report something like "unknown syscall" rather than > restart_syscall(...). > > However, this still looks like a best solution to me, just I have no idea > how much we can confuse user-space. Me neither.
