[PATCH] riscv: fix a nasty sigreturn bug...

[Al Viro]

On Fri, Sep 02, 2022 at 11:22:45AM +0200, Andrew Jones wrote:

> So, for riscv, where in do_signal and handle_signal syscall restarting
> is avoided when regs->cause != EXC_SYSCALL and it's common to set cause
> to -1 to avoid it, then it makes sense to set regs->cause != EXEC_SYSCALL
> in rt_sigreturn or in restore_sigcontext, which rt_sigreturn calls, as
> well.
> 
> So the only question I have is whether or not the cause assignment
> is better in restore_sigcontext() like other architectures? At least,
> since rt_sigreturn is the only caller of restore_sigcontext, it can't
> break anything putting it there atm...

	The only reason for doing that in restore_sigcontext() is that for
old architectures there'd been separate sigreturn(2) and rt_sigreturn(2).
Doing that in the helper shared by both avoided duplication; since
there's no such thing on riscv...

	Matter of taste, really - I have a slight preference for doing that
closer to the syscall surface, but it's no more than that.