linux-kernel - Re: [PATCH v3 1/2] RISC-V: Define sys_riscv_flush

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Date:   Tue, 14 Aug 2018 06:39:23 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Palmer Dabbelt <palmer@...ive.com>
Cc:     Christoph Hellwig <hch@...radead.org>, linux@...ck-us.net,
        aou@...s.berkeley.edu, Andrew Waterman <andrew@...ive.com>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linux@...inikbrodowski.net, tklauser@...tanz.ch,
        linux-riscv@...ts.infradead.org, dan.carpenter@...cle.com
Subject: Re: [PATCH v3 1/2] RISC-V: Define sys_riscv_flush_icache when SMP=n

>  SYSCALL_DEFINE3(riscv_flush_icache, uintptr_t, start, uintptr_t, end,
>  	uintptr_t, flags)
>  {
> +#ifdef CONFIG_SMP
>  	struct mm_struct *mm = current->mm;
>  	bool local = (flags & SYS_RISCV_FLUSH_ICACHE_LOCAL) != 0;
> +#endif
>  
>  	/* Check the reserved flags. */
>  	if (unlikely(flags & ~SYS_RISCV_FLUSH_ICACHE_ALL))
>  		return -EINVAL;
>  
> +	/*
> +	 * Without CONFIG_SMP flush_icache_mm is a just a flush_icache_all(),
> +	 * which generates unused variable warnings all over this function.
> +	 */
> +#ifdef CONFIG_SMP
>  	flush_icache_mm(mm, local);
> +#else
> +	flush_icache_all();
> +#endif

Eeek.

Something like an unconditional:

	flush_icache_mm(current->mm, flags & SYS_RISCV_FLUSH_ICACHE_LOCAL);

should solve those issues.

Also in the longer run we should turn the !SMP flush_icache_mm stub
into an inline function to solve this problem for all potential
callers.  Excepte that flush_icache_mm happens to be a RISC-V specific
API without any other callers.  So for now I think the above is what
I'd do, but this area has a lot of room for cleanup.