Re: [PATCH] ARM: fix smp_processor_id() in preemptible warning in harden_branch_predictor()

From: Liu Xiang <liuxiang1999@gmail.com>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Liu Xiang <liu.xiang@zlingsmart.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, liuxiang_1999@126.com
Subject: Re: [PATCH] ARM: fix smp_processor_id() in preemptible warning in harden_branch_predictor()
Date: Thu, 25 Mar 2021 21:32:35 +0800	[thread overview]
Message-ID: <CAPPcxxSzNvGu3y+3Fpc5FtV-6mOBPWMihmGhHnbq_qAHe3oYTA@mail.gmail.com> (raw)
In-Reply-To: <20210325100605.GL1463@shell.armlinux.org.uk>

Russell King - ARM Linux admin <linux@armlinux.org.uk> 于2021年3月25日周四 下午6:06写道：
>
> On Thu, Mar 25, 2021 at 05:50:49PM +0800, Liu Xiang wrote:
> > When CONFIG_HARDEN_BRANCH_PREDICTOR is selected and user aborts occur,
> > there is a warning:
> >
> > BUG: using smp_processor_id() in preemptible [00000000] code: errnotest/577
> > caller is __do_user_fault.constprop.4+0x24/0x88
> > CPU: 1 PID: 577 Comm: errnotest Not tainted 4.14.188-rt87-fmsh-00004-g58055877a #1
> > Hardware name: FMSH PSOC Platform
> > [<8010d6d4>] (unwind_backtrace) from [<8010a228>] (show_stack+0x10/0x14)
> > [<8010a228>] (show_stack) from [<80698f44>] (dump_stack+0x7c/0x98)
> > [<80698f44>] (dump_stack) from [<803d17d0>] (check_preemption_disabled+0xc4/0xfc)
> > [<803d17d0>] (check_preemption_disabled) from [<80110eb8>] (__do_user_fault.constprop.4+0x24/0x88)
> > [<80110eb8>] (__do_user_fault.constprop.4) from [<801112e4>] (do_page_fault+0x2dc/0x310)
> > [<801112e4>] (do_page_fault) from [<801012a8>] (do_DataAbort+0x38/0xb8)
> > [<801012a8>] (do_DataAbort) from [<8010b03c>] (__dabt_usr+0x3c/0x40)
> > Exception stack(0xb21d1fb0 to 0xb21d1ff8)
> > 1fa0:                                     fffffff4 00000000 00000054 fffffff4
> > 1fc0: 00000000 00000000 7ed81cc8 7ed81ca0 0007a440 00000000 00000000 00000000
> > 1fe0: 00000000 7ed81ca0 00010493 0001f330 20030010 ffffffff
>
> This is not the right fix - preemption is supposed to be disabled before
> this function is called. I'm not sure at the present time what the right
> fix is supposed to be because I've forgotten most of the background
> behind why this was placed where it is.
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

I have tested with the current mainline kernel, the warning still exists.
[   14.404322] BUG: using smp_processor_id() in preemptible [00000000]
code: errnotest/81
[   14.404795] caller is __do_user_fault.constprop.5+0x54/0x7c
[   14.405163] CPU: 1 PID: 81 Comm: errnotest Not tainted
5.12.0-rc4-ge97a94a30e55-dirty #6
[   14.405616] Hardware name: ARM-Versatile Express
[   14.406475] [<c010af58>] (unwind_backtrace) from [<c01064c4>]
(show_stack+0x10/0x14)
[   14.407018] [<c01064c4>] (show_stack) from [<c0a6a0cc>]
(dump_stack+0x8c/0xa0)
[   14.407398] [<c0a6a0cc>] (dump_stack) from [<c0a6d0a4>]
(check_preemption_disabled+0x114/0x118)
[   14.407906] [<c0a6d0a4>] (check_preemption_disabled) from
[<c010ef68>] (__do_user_fault.constprop.5+0x54/0x7c)
[   14.408367] [<c010ef68>] (__do_user_fault.constprop.5) from
[<c010f274>] (do_page_fault+0x208/0x3bc)
[   14.408907] [<c010f274>] (do_page_fault) from [<c010f588>]
(do_DataAbort+0x3c/0xbc)
[   14.409266] [<c010f588>] (do_DataAbort) from [<c0100e7c>]
(__dabt_usr+0x3c/0x40)
[   14.409721] Exception stack(0xc285ffb0 to 0xc285fff8)
[   14.410099] ffa0:                                     fffffff4
00000000 00000054 fffffff4
[   14.411000] ffc0: 00000000 00000000 bed90d28 bed90d00 0007a440
00000000 00000000 00000000
[   14.411386] ffe0: 00000000 bed90d00 00010493 0001f330 20030010 ffffffff
Segmentation fault