linux-kernel - Re: [PATCH] iov_iter: Fix 9p virtio breakage

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Message-ID: <20181102190433.GZ32577@ZenIV.linux.org.uk>
Date:   Fri, 2 Nov 2018 19:04:33 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     David Howells <dhowells@...hat.com>, linux-kernel@...r.kernel.org,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] iov_iter: Fix 9p virtio breakage

On Fri, Nov 02, 2018 at 05:16:51PM +0000, Marc Zyngier wrote:
> When switching to the new iovec accessors, a negation got subtly
> dropped, leading to 9p being remarkably broken (here with kvmtool):
> 
> [    7.430941] VFS: Mounted root (9p filesystem) on device 0:15.
> [    7.432080] devtmpfs: mounted
> [    7.432717] Freeing unused kernel memory: 1344K
> [    7.433658] Run /virt/init as init process
>   Warning: unable to translate guest address 0x7e00902ff000 to host
>   Warning: unable to translate guest address 0x7e00902fefc0 to host
>   Warning: unable to translate guest address 0x7e00902ff000 to host
>   Warning: unable to translate guest address 0x7e008febef80 to host
>   Warning: unable to translate guest address 0x7e008febf000 to host
>   Warning: unable to translate guest address 0x7e008febef00 to host
>   Warning: unable to translate guest address 0x7e008febf000 to host
> [    7.436376] Kernel panic - not syncing: Requested init /virt/init failed (error -8).
> [    7.437554] CPU: 29 PID: 1 Comm: swapper/0 Not tainted 4.19.0-rc8-02267-g00e23707442a #291
> [    7.439006] Hardware name: linux,dummy-virt (DT)
> [    7.439902] Call trace:
> [    7.440387]  dump_backtrace+0x0/0x148
> [    7.441104]  show_stack+0x14/0x20
> [    7.441768]  dump_stack+0x90/0xb4
> [    7.442425]  panic+0x120/0x27c
> [    7.443036]  kernel_init+0xa4/0x100
> [    7.443725]  ret_from_fork+0x10/0x18
> [    7.444444] SMP: stopping secondary CPUs
> [    7.445391] Kernel Offset: disabled
> [    7.446169] CPU features: 0x0,23000438
> [    7.446974] Memory Limit: none
> [    7.447645] ---[ end Kernel panic - not syncing: Requested init /virt/init failed (error -8). ]---
> 
> Restoring the missing "!" brings the guest back to life.
> 
> Fixes: 00e23707442a ("iov_iter: Use accessor function")
> Reported-by: Will Deacon <will.deacon@....com>
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>

ACK.  Do you want me to take it via vfs.git?  Or might as well
send directly to Linus, with

Acked-by Al Viro <viro@...iv.linux.org.uk>

on it.