Date:   Thu, 31 Mar 2022 08:39:56 +0000
From:   "Liu, Chuansheng" <chuansheng.liu@...el.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
CC:     "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "deller@....de" <deller@....de>, "x86@...nel.org" <x86@...nel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "andrii@...nel.org" <andrii@...nel.org>,
        Song Liu <song@...nel.org>, "Ingo Molnar" <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "tzimmermann@...e.de" <tzimmermann@...e.de>,
        Borislav Petkov <bp@...en8.de>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "kernel-team@...com" <kernel-team@...com>
Subject: RE: [PATCH] fbdev: defio: fix the pagelist corruption

Hi Paul,

> -----Original Message-----
> From: dri-devel <dri-devel-bounces@...ts.freedesktop.org> On Behalf Of Paul
> Menzel
> Sent: Thursday, March 31, 2022 4:22 PM
> To: Liu, Chuansheng <chuansheng.liu@...el.com>
> Cc: linux-fbdev@...r.kernel.org; Dave Hansen <dave.hansen@...ux.intel.com>;
> akpm@...ux-foundation.org; daniel@...earbox.net; linux-mm@...ck.org;
> netdev@...r.kernel.org; deller@....de; x86@...nel.org; ast@...nel.org; dri-
> devel@...ts.freedesktop.org; andrii@...nel.org; Song Liu <song@...nel.org>;
> Ingo Molnar <mingo@...hat.com>; Thomas Gleixner <tglx@...utronix.de>;
> tzimmermann@...e.de; Borislav Petkov <bp@...en8.de>; bpf@...r.kernel.org;
> Edgecombe, Rick P <rick.p.edgecombe@...el.com>; kernel-team@...com
> Subject: Re: [PATCH] fbdev: defio: fix the pagelist corruption
> 
> Dear Chuansheng,
> 
> 
> Am 31.03.22 um 02:06 schrieb Liu, Chuansheng:
> 
> >> -----Original Message-----
> >> From: Paul Menzel <pmenzel@...gen.mpg.de>
> >> Sent: Thursday, March 31, 2022 12:47 AM
> 
> […]
> 
> >> Am 29.03.22 um 01:58 schrieb Liu, Chuansheng:
> >>
> >>>> -----Original Message-----
> >>>> From: Paul Menzel
> >>>> Sent: Monday, March 28, 2022 2:15 PM
> >>
> >>>> Am 28.03.22 um 02:58 schrieb Liu, Chuansheng:
> >>>>
> >>>>>> -----Original Message-----
> >>>>
> >>>>>> Sent: Saturday, March 26, 2022 4:11 PM
> >>>>
> >>>>>> Am 17.03.22 um 06:46 schrieb Chuansheng Liu:
> >>>>>>> Easily hit the below list corruption:
> >>>>>>> ==
> >>>>>>> list_add corruption. prev->next should be next (ffffffffc0ceb090), but
> >>>>>>> was ffffec604507edc8. (prev=ffffec604507edc8).
> >>>>>>> WARNING: CPU: 65 PID: 3959 at lib/list_debug.c:26
> >>>>>>> __list_add_valid+0x53/0x80
> >>>>>>> CPU: 65 PID: 3959 Comm: fbdev Tainted: G     U
> >>>>>>> RIP: 0010:__list_add_valid+0x53/0x80
> >>>>>>> Call Trace:
> >>>>>>>      <TASK>
> >>>>>>>      fb_deferred_io_mkwrite+0xea/0x150
> >>>>>>>      do_page_mkwrite+0x57/0xc0
> >>>>>>>      do_wp_page+0x278/0x2f0
> >>>>>>>      __handle_mm_fault+0xdc2/0x1590
> >>>>>>>      handle_mm_fault+0xdd/0x2c0
> >>>>>>>      do_user_addr_fault+0x1d3/0x650
> >>>>>>>      exc_page_fault+0x77/0x180
> >>>>>>>      ? asm_exc_page_fault+0x8/0x30
> >>>>>>>      asm_exc_page_fault+0x1e/0x30
> >>>>>>> RIP: 0033:0x7fd98fc8fad1
> >>>>>>> ==
> >>>>>>>
> >>>>>>> Figure out the race happens when one process is adding &page->lru
> into
> >>>>>>> the pagelist tail in fb_deferred_io_mkwrite(), another process is
> >>>>>>> re-initializing the same &page->lru in fb_deferred_io_fault(), which is
> >>>>>>> not protected by the lock.
> >>>>>>>
> >>>>>>> This fix is to init all the page lists one time during initialization,
> >>>>>>> it not only fixes the list corruption, but also avoids INIT_LIST_HEAD()
> >>>>>>> redundantly.
> >>>>>>>
> >>>>>>> Fixes: 105a940416fc ("fbdev/defio: Early-out if page is already
> enlisted")
> >>>>>>> Cc: Thomas Zimmermann <tzimmermann@...e.de>
> >>>>>>> Signed-off-by: Chuansheng Liu <chuansheng.liu@...el.com>
> >>>>>>> ---
> >>>>>>>      drivers/video/fbdev/core/fb_defio.c | 9 ++++++++-
> >>>>>>>      1 file changed, 8 insertions(+), 1 deletion(-)
> >>>>>>>
> >>>>>>> diff --git a/drivers/video/fbdev/core/fb_defio.c
> b/drivers/video/fbdev/core/fb_defio.c
> >>>>>>> index 98b0f23bf5e2..eafb66ca4f28 100644
> >>>>>>> --- a/drivers/video/fbdev/core/fb_defio.c
> >>>>>>> +++ b/drivers/video/fbdev/core/fb_defio.c
> >>>>>>> @@ -59,7 +59,6 @@ static vm_fault_t fb_deferred_io_fault(struct
> vm_fault *vmf)
> >>>>>>>      		printk(KERN_ERR "no mapping available\n");
> >>>>>>>
> >>>>>>>      	BUG_ON(!page->mapping);
> >>>>>>> -	INIT_LIST_HEAD(&page->lru);
> >>>>>>>      	page->index = vmf->pgoff;
> >>>>>>>
> >>>>>>>      	vmf->page = page;
> >>>>>>> @@ -220,6 +219,8 @@ static void fb_deferred_io_work(struct
> work_struct *work)
> >>>>>>>      void fb_deferred_io_init(struct fb_info *info)
> >>>>>>>      {
> >>>>>>>      	struct fb_deferred_io *fbdefio = info->fbdefio;
> >>>>>>> +	struct page *page;
> >>>>>>> +	int i;
> >>>>>>>
> >>>>>>>      	BUG_ON(!fbdefio);
> >>>>>>>      	mutex_init(&fbdefio->lock);
> >>>>>>> @@ -227,6 +228,12 @@ void fb_deferred_io_init(struct fb_info *info)
> >>>>>>>      	INIT_LIST_HEAD(&fbdefio->pagelist);
> >>>>>>>      	if (fbdefio->delay == 0) /* set a default of 1 s */
> >>>>>>>      		fbdefio->delay = HZ;
> >>>>>>> +
> >>>>>>> +	/* initialize all the page lists one time */
> >>>>>>> +	for (i = 0; i < info->fix.smem_len; i += PAGE_SIZE) {
> >>>>>>> +		page = fb_deferred_io_page(info, i);
> >>>>>>> +		INIT_LIST_HEAD(&page->lru);
> >>>>>>> +	}
> >>>>>>>      }
> >>>>>>>      EXPORT_SYMBOL_GPL(fb_deferred_io_init);
> >>>>>>>
> >>>>>> Applying your patch on top of current Linus’ master branch, tty0 is
> >>>>>> unusable and looks frozen. Sometimes network card still works,
> sometimes
> >>>>>> not.
> >>>>>
> >>>>> I don't see how the patch would cause below BUG call stack, need some
> time to
> >>>>> debug. Just few comments:
> >>>>> 1. Will the system work well without this patch?
> >>>>
> >>>> Yes, the framebuffer works well without the patch.
> >>>>
> >>>>> 2. When you are sure the patch causes the regression you saw, please get
> free
> >>>> to submit one reverted patch, thanks : )
> >>>>
> >>>> I think you for patch wasn’t submitted yet – at least not pulled by Linus.
> >>> The patch has been in drm-tip, could you have a try with the latest drm-tip
> to see
> >>> if the Framebuffer works well, in that case, we could revert it in drm-tip then.
> >>
> >> With drm-tip (drm-tip: 2022y-03m-29d-13h-14m-35s UTC integration
> >> manifest) everything works fine. (I had to disable amdgpu driver, as it
> >> failed to build.) Is anyone able to explain that?
> >
> > My patch is for fixing another patch which is in the drm-tip at least,
> 
> The referenced commit 105a940416fc in the Fixes tag is also in Linus’
> master branch.
> 
> > so I assume applying my patch into Linus tree directly is not
> > completely proper. That's my intention of asking your help for
> > retesting drm-tip.
> If there were such a relation, that would need to be documented in the
> commit message.
You should have seen it : )

> 
> > You mean everything working fine means another issue you hit is also
> > gone?
> No, I just mean the hang when applying your patch.
> 
> Anyway, after figuring out, that drm-tip, is actually not behind Linus’
> master branch, I tried to figure out the differences, and it turns out
> it’s also related to commit fac54e2bfb5b (x86/Kconfig: Select
> HAVE_ARCH_HUGE_VMALLOC with HAVE_ARCH_HUGE_VMAP) [1], which is in
> Linus’
> master branch, but not drm-tip. Note, I am using a 32-bit user space and
> a 64-bit Linux kernel. Reverting commit fac54e2bfb5b, and having your
> patch a applied, the hang is gone.
Good to know you have figured it out, and the issue you hit is not related to
my patch : )

> 
> I am adding the people involved in the other discussion to make them
> aware of this failure case.
> 
> 
> Kind regards,
> 
> Paul
> 
> 
> [1]: https://linux-regtracking.leemhuis.info/regzbot/mainline/

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