Re: [PATCH] mt76: usb: fix possible memory leak during suspend/resume

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On Fri, Apr 12, 2019 at 06:27:48PM +0200, Lorenzo Bianconi wrote:
> > > > On Fri, Apr 12, 2019 at 02:27:16PM +0200, Lorenzo Bianconi wrote:
> > > > > Disable mt76u_tx_tasklet at the end of mt76u_stop_queues in order to
> > > > > properly deallocate all pending skbs during suspend/resume phase
> > > > 
> > > > On suspend/resume tx skb's are processed after tasklet_enable()
> > > > in resume callback. There is issue with device removal though
> > > > (during suspend or otherwise).
> > > 
> > > Hi Stanislaw,
> > > 
> > > I guess the right moment to deallocate the skbs is during suspend since resume
> > > can happen in very far future
> 
> Yes, it's better to free on suspend, but in practice does not really matter since
> system is disabled till resume.
> 
> > > > > Fixes: b40b15e1521f ("mt76: add usb support to mt76 layer")
> > > > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > > > ---
> > > > >  drivers/net/wireless/mediatek/mt76/usb.c | 4 ++--
> > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/net/wireless/mediatek/mt76/usb.c b/drivers/net/wireless/mediatek/mt76/usb.c
> > > > > index a3acc070063a..575207133775 100644
> > > > > --- a/drivers/net/wireless/mediatek/mt76/usb.c
> > > > > +++ b/drivers/net/wireless/mediatek/mt76/usb.c
> > > > > @@ -842,10 +842,10 @@ static void mt76u_stop_tx(struct mt76_dev *dev)
> > > > >  void mt76u_stop_queues(struct mt76_dev *dev)
> > > > >  {
> > > > >  	tasklet_disable(&dev->usb.rx_tasklet);
> > > > > -	tasklet_disable(&dev->usb.tx_tasklet);
> > > > > -
> > > > >  	mt76u_stop_rx(dev);
> > > > > +
> > > > >  	mt76u_stop_tx(dev);
> > > > > +	tasklet_disable(&dev->usb.tx_tasklet);
> > > > 
> > > > If tasklet is scheduled and we disable it and never enable, we end up
> > > > with infinite loop in tasklet_action_common(). This patch make the
> > > > problem less reproducible since tasklet_disable() is moved after
> > > > usb_kill_urb() -> tasklet_schedule(), but it is still possible.
> > > 
> > > I can see the point here. Maybe we can just run tasklet_kill instead of
> > > tasklet_disable here (at least for tx one)
> 
> I think you have right as tasklet_kill() will wait for scheduled tasklet .
> Originally in my patch (see below) I used wait_event as I thought
> tasklet_kill() may prevent scheduled tasklet to be executed (hence cause
> leak) but that seems to be not true.

I agree with rx side (good catch!!), but on tx one I guess usb_kill_urb()
is already waiting for tx pending so we just need to use tasklet_kill
at the end of mt76u_stop_queues, in this way we will free pending skbs during
suspend

Regards,
Lorenzo

> 
> > I think it is enough even for rx side since usb_kill_urb() will wait the end of
> > mt76u_complete_rx() and tasklet_kill() will wait for the completion of
> > mt76u_rx_tasklet(). We will need to remove tasklet_enable in resume routines.
> 
> No, because rx urb's are resubmitted on mt76u_rx_tasklet(). I use usb_poison_urb()
> to prevent that in my patch.
> 
> Stanislaw
> 
> commit 088b1209302e17cda688c9b562e18970c92823ac
> Author: Stanislaw Gruszka <sgruszka@redhat.com>
> Date:   Thu Apr 4 13:37:43 2019 +0200
> 
>     mt76usb: fix tx/rx stop
>     
>     Disabling tasklets on stopping rx/tx is wrong. If blocked tasklet
>     is scheduled and we remove device we get 100% cpu usage:
>     
>       PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
>         9 root      20   0       0      0      0 R  93.8   0.0   1:47.19 ksoftirqd/0
>     
>     by using memory after free and eventually crash:
>     
>     [ 2068.591964] RIP: 0010:tasklet_action_common.isra.17+0x66/0x100
>     [ 2068.591966] Code: 41 89 f5 eb 25 f0 48 0f ba 33 00 0f 83 b1 00 00 00 48 8b 7a 20 48 8b 42 18 e8 56 a3 b5 00 f0 80 23 fd 48 89 ea 48 85 ed 74 53 <48> 8b 2a 48 8d 5a 08 f0 48 0f ba 6a 08 01 72 0b 8b 42 10 85 c0 74
>     [ 2068.591968] RSP: 0018:ffff98758c34be58 EFLAGS: 00010206
>     [ 2068.591969] RAX: ffff98758e6966d0 RBX: ffff98756e69aef8 RCX: 0000000000000006
>     [ 2068.591970] RDX: 01060a053d060305 RSI: 0000000000000006 RDI: ffff98758e6966d0
>     [ 2068.591971] RBP: 01060a053d060305 R08: 0000000000000000 R09: 00000000000203c0
>     [ 2068.591971] R10: 000003ff65b34f08 R11: 0000000000000001 R12: ffff98758e6966d0
>     [ 2068.591972] R13: 0000000000000006 R14: 0000000000000040 R15: 0000000000000006
>     [ 2068.591974] FS:  0000000000000000(0000) GS:ffff98758e680000(0000) knlGS:0000000000000000
>     [ 2068.591975] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>     [ 2068.591975] CR2: 00002c5f73a6cc20 CR3: 00000002f920a001 CR4: 00000000003606e0
>     [ 2068.591977] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>     [ 2068.591978] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>     [ 2068.591978] Call Trace:
>     [ 2068.591985]  __do_softirq+0xe3/0x30a
>     [ 2068.591989]  ? sort_range+0x20/0x20
>     [ 2068.591990]  run_ksoftirqd+0x26/0x40
>     [ 2068.591992]  smpboot_thread_fn+0xc5/0x160
>     [ 2068.591995]  kthread+0x112/0x130
>     [ 2068.591997]  ? kthread_create_on_node+0x40/0x40
>     [ 2068.591998]  ret_from_fork+0x35/0x40
>     [ 2068.591999] Modules linked in: ccm arc4 fuse rfcomm cmac bnep sunrpc snd_hda_codec_hdmi snd_soc_skl snd_soc_core snd_soc_acpi_intel_match snd_hda_codec_realtek snd_soc_acpi snd_hda_codec_generic snd_soc_skl_ipc snd_soc_sst_ipc snd_soc_sst_dsp snd_hda_ext_core iTCO_wdt snd_hda_intel intel_rapl iTCO_vendor_support x86_pkg_temp_thermal intel_powerclamp btusb mei_wdt coretemp btrtl snd_hda_codec btbcm btintel intel_cstate snd_hwdep intel_uncore uvcvideo snd_hda_core videobuf2_vmalloc videobuf2_memops intel_rapl_perf wmi_bmof videobuf2_v4l2 intel_wmi_thunderbolt snd_seq bluetooth joydev videobuf2_common snd_seq_device snd_pcm videodev media i2c_i801 snd_timer idma64 ecdh_generic intel_lpss_pci intel_lpss mei_me mei ucsi_acpi typec_ucsi processor_thermal_device intel_soc_dts_iosf intel_pch_thermal typec thinkpad_acpi wmi snd soundcore rfkill int3403_thermal int340x_thermal_zone int3400_thermal acpi_thermal_rel acpi_pad pcc_cpufreq uas usb_storage crc32c_intel i915 i2c_algo_bit nvme serio_raw
>     [ 2068.592033]  drm_kms_helper e1000e nvme_core drm video ipv6 [last unloaded: cfg80211]
>     
>     Fortunate thing is that this not happen frequently, as scheduling
>     tasklet on blocked state is very exceptional, though might happen.
>     
>     Due to different RX/TX tasklet processing fix is different for those.
>     For TX just wait until queues are empty. For RX assure rx_tasklet
>     do fail to resubmit buffers by poisoning urb's and kill the tasklet.
>     
>     Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mac80211.c b/drivers/net/wireless/mediatek/mt76/mac80211.c
> index 15825e9a458f..7bf91566e212 100644

[...]

> @@ -830,20 +831,35 @@ static void mt76u_free_tx(struct mt76_dev *dev)
>  static void mt76u_stop_tx(struct mt76_dev *dev)
>  {
>  	struct mt76_queue *q;
> -	int i, j;
> +	int i, j, ret;
>  
>  	for (i = 0; i < IEEE80211_NUM_ACS; i++) {
>  		q = dev->q_tx[i].q;
>  		for (j = 0; j < q->ndesc; j++)
>  			usb_kill_urb(q->entry[j].urb);
>  	}
> +
> +	ret = wait_event_timeout(dev->tx_wait, !mt76_has_tx_pending(dev), HZ/5);
> +	if (!ret)
> +		dev_err(dev->dev, "timed out waiting for pending tx\n");
>  }
>  
> -void mt76u_stop_queues(struct mt76_dev *dev)
> +int mt76u_start_queues(struct mt76_dev *dev)

maybe mt76u_resume_rx_queue would be more clear

>  {
> -	tasklet_disable(&dev->usb.rx_tasklet);
> -	tasklet_disable(&dev->usb.tx_tasklet);
> +	struct mt76_queue *q = &dev->q_rx[MT_RXQ_MAIN];
> +	int i;
> +
> +	/* Nothing to do for TX */
>  
> +	for (i = 0; i < q->ndesc; i++)
> +		usb_unpoison_urb(q->entry[i].urb);
> +
> +	return mt76u_submit_rx_buffers(dev);
> +}
> +EXPORT_SYMBOL_GPL(mt76u_start_queues);
> +
> +void mt76u_stop_queues(struct mt76_dev *dev)
> +{
>  	mt76u_stop_rx(dev);
>  	mt76u_stop_tx(dev);
>  }


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