linux-kernel - Re: [RFC PATCH for 4.21 06/16] cpu_opv: Provide cpu

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Date:   Wed, 17 Oct 2018 10:46:51 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
        Chris Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [RFC PATCH for 4.21 06/16] cpu_opv: Provide cpu_opv system call
 (v8)

Hi Mathieu,

On (10/16/18 15:17), Mathieu Desnoyers wrote:
>
> Therefore, only an internal kernel bug between vm_map_user_ram() and
> vm_unmap_user_ram() should trigger the BUG_ON(). No user input is passed
> to vm_unmap_user_ram().
>
> Now, let's look at vm_map_user_ram(). It calls alloc_vmap_area(), which returns
> a vmap_area. Then if vmap_page_range failed, vm_unmap_user_ram is called on the
> memory that has just been returned by vm_map_user_ram. Again, only an internal
> bug between map/unmap can trigger the BUG_ON() in vm_unmap_user_ram.

Thanks for spending time on this.
Just wanted someone to have extra look at syscall->BUG_ON().

	-ss