linux-kernel - Re: [PATCH] riscv: fix locking violation in page fault handler

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Message-ID: <mhng-56794b7f-6cd4-4eb9-a962-83ad256ed3cd@palmer-si-x1e>
Date:   Tue, 07 May 2019 16:48:03 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     schwab@...e.de
CC:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject:     Re: [PATCH] riscv: fix locking violation in page fault handler

On Tue, 07 May 2019 00:36:46 PDT (-0700), schwab@...e.de wrote:
> When a user mode process accesses an address in the vmalloc area
> do_page_fault tries to unlock the mmap semaphore when it isn't locked.
>
> Signed-off-by: Andreas Schwab <schwab@...e.de>
> ---
>  arch/riscv/mm/fault.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index 88401d5125bc..c51878e5a66a 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -181,6 +181,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
>  	up_read(&mm->mmap_sem);
>  	/* User mode accesses just cause a SIGSEGV */
>  	if (user_mode(regs)) {
> +bad_area_do_trap:
>  		do_trap(regs, SIGSEGV, code, addr, tsk);
>  		return;
>  	}
> @@ -230,7 +231,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
>  		int index;
>
>  		if (user_mode(regs))
> -			goto bad_area;
> +			goto bad_area_do_trap;
>
>  		/*
>  		 * Synchronize this task's top level page-table

I got lost with all the gotos, I think something like this is cleaner

    diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
    index 26293bc053a8..cec8be9e2d6a 100644
    --- a/arch/riscv/mm/fault.c
    +++ b/arch/riscv/mm/fault.c
    @@ -229,8 +229,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
                    pte_t *pte_k;
                    int index;
    
    +               /* User mode accesses just cause a SIGSEGV */
                    if (user_mode(regs))
    -                       goto bad_area;
    +                       return do_trap(regs, SIGSEGV, code, addr, tsk);
    
                    /*
                     * Synchronize this task's top level page-table

Unless anyone has a better idea?

Either way:

Reviewed-by: Palmer Dabbelt <palmer@...ive.com>

LMK if you, or anyone else, has a preference.  I'm assuming this will go in
through my tree, so I've picked up my version for now :)