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Date:   Sun, 23 Apr 2023 22:51:02 +0200
From:   Janne Grunau <j@jannau.net>
To:     Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc:     Zongmin Zhou <zhouzongmin@kylinos.cn>,
        maarten.lankhorst@linux.intel.com, mripard@kernel.org,
        tzimmermann@suse.de, airlied@gmail.com, daniel@ffwll.ch,
        neil.armstrong@linaro.org, tony.luck@intel.com,
        keescook@chromium.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, gpiccoli@igalia.com,
        linux-hardening@vger.kernel.org, laurentiu.palcu@oss.nxp.com,
        regressions@lists.linux.dev
Subject: Re: [PATCH] drm/probe_helper: fix the warning reported when calling
 drm_kms_helper_poll_disable during suspend
Message-ID: <20230423205102.GE3280@jannau.net>
References: <20230328023129.3596968-1-zhouzongmin@kylinos.cn>
 <20230420200148.GD3280@jannau.net>
 <CAA8EJpoK3yv3E==bJuDoQhsW2Q1LdqKakJgdZx6S=ec-CvyGyw@mail.gmail.com>
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On 2023-04-20 23:07:01 +0300, Dmitry Baryshkov wrote:
> On Thu, 20 Apr 2023 at 23:01, Janne Grunau <j@jannau.net> wrote:
> >
> > On 2023-03-28 10:31:29 +0800, Zongmin Zhou wrote:
> > > When drivers call drm_kms_helper_poll_disable from
> > > their device suspend implementation without enabled output polling before,
> > > following warning will be reported,due to work->func not be initialized:
> >
> > we see the same warning with the wpork in progress kms driver for apple
> > silicon SoCs. The connectors do not need to polled so the driver never
> > calls drm_kms_helper_poll_init().
> >
> > > [   55.141361] WARNING: CPU: 3 PID: 372 at kernel/workqueue.c:3066 __flush_work+0x22f/0x240
> > > [   55.141382] Modules linked in: nls_iso8859_1 snd_hda_codec_generic ledtrig_audio snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec snd_hda_core snd_hwdep snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq intel_rapl_msr intel_rapl_common bochs drm_vram_helper drm_ttm_helper snd_seq_device nfit ttm crct10dif_pclmul snd_timer ghash_clmulni_intel binfmt_misc sha512_ssse3 aesni_intel drm_kms_helper joydev input_leds syscopyarea crypto_simd snd cryptd sysfillrect sysimgblt mac_hid serio_raw soundcore qemu_fw_cfg sch_fq_codel msr parport_pc ppdev lp parport drm ramoops reed_solomon pstore_blk pstore_zone efi_pstore virtio_rng ip_tables x_tables autofs4 hid_generic usbhid hid ahci virtio_net i2c_i801 crc32_pclmul psmouse virtio_scsi libahci i2c_smbus lpc_ich xhci_pci net_failover virtio_blk xhci_pci_renesas failover
> > > [   55.141430] CPU: 3 PID: 372 Comm: kworker/u16:9 Not tainted 6.2.0-rc6+ #16
> > > [   55.141433] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
> > > [   55.141435] Workqueue: events_unbound async_run_entry_fn
> > > [   55.141441] RIP: 0010:__flush_work+0x22f/0x240
> > > [   55.141444] Code: 8b 43 28 48 8b 53 30 89 c1 e9 f9 fe ff ff 4c 89 f7 e8 b5 95 d9 00 e8 00 53 08 00 45 31 ff e9 11 ff ff ff 0f 0b e9 0a ff ff ff <0f> 0b 45 31 ff e9 00 ff ff ff e8 e2 54 d8 00 66 90 90 90 90 90 90
> > > [   55.141446] RSP: 0018:ff59221940833c18 EFLAGS: 00010246
> > > [   55.141449] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff9b72bcbe
> > > [   55.141450] RDX: 0000000000000001 RSI: 0000000000000001 RDI: ff3ea01e4265e330
> > > [   55.141451] RBP: ff59221940833c90 R08: 0000000000000000 R09: 8080808080808080
> > > [   55.141453] R10: ff3ea01e42b3caf4 R11: 000000000000000f R12: ff3ea01e4265e330
> > > [   55.141454] R13: 0000000000000001 R14: ff3ea01e505e5e80 R15: 0000000000000001
> > > [   55.141455] FS:  0000000000000000(0000) GS:ff3ea01fb7cc0000(0000) knlGS:0000000000000000
> > > [   55.141456] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > [   55.141458] CR2: 0000563543ad1546 CR3: 000000010ee82005 CR4: 0000000000771ee0
> > > [   55.141464] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > [   55.141465] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > [   55.141466] PKRU: 55555554
> > > [   55.141467] Call Trace:
> > > [   55.141469]  <TASK>
> > > [   55.141472]  ? pcie_wait_cmd+0xdf/0x220
> > > [   55.141478]  ? mptcp_seq_show+0xe0/0x180
> > > [   55.141484]  __cancel_work_timer+0x124/0x1b0
> > > [   55.141487]  cancel_delayed_work_sync+0x17/0x20
> > > [   55.141490]  drm_kms_helper_poll_disable+0x26/0x40 [drm_kms_helper]
> > > [   55.141516]  drm_mode_config_helper_suspend+0x25/0x90 [drm_kms_helper]
> > > [   55.141531]  ? __pm_runtime_resume+0x64/0x90
> > > [   55.141536]  bochs_pm_suspend+0x16/0x20 [bochs]
> > > [   55.141540]  pci_pm_suspend+0x8b/0x1b0
> > > [   55.141545]  ? __pfx_pci_pm_suspend+0x10/0x10
> > > [   55.141547]  dpm_run_callback+0x4c/0x160
> > > [   55.141550]  __device_suspend+0x14c/0x4c0
> > > [   55.141553]  async_suspend+0x24/0xa0
> > > [   55.141555]  async_run_entry_fn+0x34/0x120
> > > [   55.141557]  process_one_work+0x21a/0x3f0
> > > [   55.141560]  worker_thread+0x4e/0x3c0
> > > [   55.141563]  ? __pfx_worker_thread+0x10/0x10
> > > [   55.141565]  kthread+0xf2/0x120
> > > [   55.141568]  ? __pfx_kthread+0x10/0x10
> > > [   55.141570]  ret_from_fork+0x29/0x50
> > > [   55.141575]  </TASK>
> > > [   55.141575] ---[ end trace 0000000000000000 ]---
> > >
> > > Fixes: a4e771729a51 ("drm/probe_helper: sort out poll_running vs poll_enabled")
> > > Signed-off-by: Zongmin Zhou<zhouzongmin@kylinos.cn>
> > > ---
> > >  drivers/gpu/drm/drm_probe_helper.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> > > index 8127be134c39..ac72b18e2257 100644
> > > --- a/drivers/gpu/drm/drm_probe_helper.c
> > > +++ b/drivers/gpu/drm/drm_probe_helper.c
> > > @@ -855,7 +855,8 @@ void drm_kms_helper_poll_disable(struct drm_device *dev)
> > >       if (dev->mode_config.poll_running)
> > >               drm_kms_helper_disable_hpd(dev);
> > >
> > > -     cancel_delayed_work_sync(&dev->mode_config.output_poll_work);
> > > +     if (dev->mode_config.poll_enabled)
> > > +             cancel_delayed_work_sync(&dev->mode_config.output_poll_work);
> >
> > Checking for dev->mode_config.poll_enabled at the start of the function
> > and return early if it is not true looks more in style with the rest of
> > drm_probe_helper.c.
> 
> I think it is an error to call drm_kms_helper_poll_disable() if
> polling was not initialized. So, in my opinion the fix should go to
> the drm_mode_config_helper_suspend() / _resume() instead. Please add a
> guard there using dev->mode_config.poll_enabled.

While I tend to agree to the sentiment I do not think this is the 
correct fix in this situation. drm_kms_helper_poll_disable had the
check since at least 2014. a4e771729a51 is a regression. If we want to  
change the behavior it should be done explicitly and after verifying all 
drm_kms_helper_poll_disable() calls.

#regzbot ^introduced a4e771729a51

ciao
Janne