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Date:   Wed, 17 Oct 2018 10:46:51 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-api <linux-api@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@amacapital.net>,
        Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Russell King <linux@arm.linux.org.uk>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <andi@firstfloor.org>,
        Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>,
        rostedt <rostedt@goodmis.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Joel Fernandes <joelaf@google.com>
Subject: Re: [RFC PATCH for 4.21 06/16] cpu_opv: Provide cpu_opv system call
 (v8)
Message-ID: <20181017014651.GB1068@jagdpanzerIV>
References: <20181010191936.7495-1-mathieu.desnoyers@efficios.com>
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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