Re: [PATCH v2 2/4] driver core: enable drivers to use deferred probe from init

Luis R. Rodriguez
2014-08-11T17:20:42Z

On Mon, Aug 11, 2014 at 11:27 AM, Takashi Iwai <tiwai@suse.de> wrote:
> Luis R. Rodriguez wrote:
>>
>> On Sun, Aug 10, 2014 at 08:43:31PM +0800, Greg KH wrote:
>> > On Sat, Aug 09, 2014 at 06:41:19PM +0200, Luis R. Rodriguez wrote:
>> > > On Wed, Jul 30, 2014 at 03:11:07PM -0700, David Miller wrote:
>> > > > From: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>
>> > > > Date: Mon, 28 Jul 2014 11:28:28 -0700
>> > > >
>> > > > > Tetsuo bisected and found that commit 786235ee "kthread: make
>> > > > > kthread_create() killable" modified kthread_create() to bail as
>> > > > > soon as SIGKILL is received. This is causing some issues with
>> > > > > some drivers and at times boot. Joseph then found that failures
>> > > > > occur as the systemd-udevd process sends SIGKILL to modprobe if
>> > > > > probe on a driver takes over 30 seconds. When this happens probe
>> > > > > will fail on any driver, its why booting on some system will fail
>> > > > > if the driver happens to be a storage related driver. Some folks
>> > > > > have suggested fixing this by modifying kthread_create() to not
>> > > > > leave upon SIGKILL [3], upon review Oleg rejected this change and
>> > > > > the discussion was punted out to systemd to see if the default
>> > > > > timeout could be increased from 30 seconds to 120. The opinion of
>> > > > > the systemd maintainers is that the driver's behavior should
>> > > > > be fixed [4]. Linus seems to agree [5], however more recently even
>> > > > > networking drivers have been reported to fail on probe since just
>> > > > > writing the firmware to a device and kicking it can take easy over
>> > > > > 60 seconds [6]. Benjamim was able to trace the issues recently
>> > > > > reported on cxgb4 down to the same systemd-udevd 30 second timeout [6].
>> > > > >
>> > > > > This is an alternative solution which enables drivers that are
>> > > > > known to take long to use deferred probe workqueue. This avoids
>> > > > > the 30 second timeout and lets us annotate drivers with long
>> > > > > init sequences.
>> > > > >
>> > > > > As drivers determine a component is not yet available and needs
>> > > > > to defer probe you'll be notified this happen upon init for each
>> > > > > device but now with a message such as:
>> > > > >
>> > > > > pci 0000:03:00.0: Driver cxgb4 requests probe deferral on init
>> > > > >
>> > > > > You should see one of these per struct device probed.
>> > > >
>> > > > It seems we're still discussing this.
>> > > >
>> > > > I think I understand all of the underlying issues, and what I'll say
>> > > > is that perhaps we should use what Greg KH requested but via a helper
>> > > > that is easy to grep for.
>> > > >
>> > > > I don't care if it's something like "module_long_probe_init()" and
>> > > > "module_long_probe_exit()", but it just needs to be some properly
>> > > > named interface which does the whole kthread or whatever bit.
>> > >
>> > > I've tested the alternative kthread_run() proposal but unfortunately it
>> > > does not help resolve the issue, the timeout is still hit and a SIGKILL
>> > > still kills the driver probe. Please let me know how you'd all like us
>> > > to proceed, these defer probe patches do help cure the issue though.
>> >
>> > Why doesn't it work? Doesn't modprobe come right back and the init
>> > sequence still takes a while to run? What exactly fails?
>>
>> systemd uses kmod kmod_module_probe_insert_module(), what I see is that using
>> kthread_run() as a work around still causes probe to fail on a driver that
>> otherwise would work fine if all you do is sprinkle ssleep(33) (seconds) on the
>> init sequence. To see the issue you can test this on any of your network
>> drivers that get loaded automatically, I did my testing with iwlwifi by
>> purposely breaking it and then using the work around. It seems the probe
>> somehow still gets killed as before, I haven't debugged this further.
>>
>> For example by breaking and fixing iwlwifi this yields:
>>
>> ergon:~ # journalctl -b -0 -u systemd-udevd
>>
>> -- Logs begin at Mon 2014-08-04 21:55:28 EDT, end at Sun 2014-08-10 10:50:14 EDT. --
>> Aug 10 10:48:49 ergon systemd-udevd[257]: specified group 'input' unknown
>> Aug 10 10:48:55 ergon mtp-probe[493]: checking bus 3, device 2: "/sys/devices/pci0000:00/0000:00:14.0/usb3/3-7"
>> Aug 10 10:48:55 ergon mtp-probe[492]: checking bus 3, device 4: "/sys/devices/pci0000:00/0000:00:14.0/usb3/3-12"
>> Aug 10 10:49:24 ergon systemd-udevd[465]: seq 1755 '/devices/pci0000:00/0000:00:1c.1/0000:03:00.0' killed
>>
>> ergon:~ # dmesg | grep iwlwifi
>> [ 10.315538] iwlwifi Going to sleep for 33 seconds
>> [ 43.323958] iwlwifi Done sleeping
>> [ 43.324400] iwlwifi 0000:03:00.0: irq 50 for MSI/MSI-X
>> [ 43.324534] iwlwifi 0000:03:00.0: Error allocating IRQ 50
>> [ 43.326951] iwlwifi: probe of 0000:03:00.0 failed with error -4
>>
>> The patch used:
>>
>> diff --git a/drivers/net/wireless/iwlwifi/mvm/ops.c b/drivers/net/wireless/iwlwifi/mvm/ops.c
>> index 610dbcb..65e0ab2 100644
>> --- a/drivers/net/wireless/iwlwifi/mvm/ops.c
>> +++ b/drivers/net/wireless/iwlwifi/mvm/ops.c
>> @@ -63,6 +63,7 @@
>> #include <linux/module.h>
>> #include <linux/vmalloc.h>
>> #include <net/mac80211.h>
>> +#include <linux/kthread.h>
>>
>> #include "iwl-notif-wait.h"
>> #include "iwl-trans.h"
>> @@ -111,7 +112,7 @@ MODULE_PARM_DESC(power_scheme,
>> /*
>> * module init and exit functions
>> */
>> -static int __init iwl_mvm_init(void)
>> +static int iwl_mvm_init_real(void *arg)
>> {
>> int ret;
>>
>> @@ -130,12 +131,21 @@ static int __init iwl_mvm_init(void)
>>
>> return ret;
>> }
>> +
>> +static struct task_struct *init_thread;
>> +
>> +static int __init iwl_mvm_init(void)
>> +{
>> + init_thread = kthread_run(iwl_mvm_init_real, NULL, "iwl_mvm_init");
>> + return 0;
>> +}
>> module_init(iwl_mvm_init);
>>
>> static void __exit iwl_mvm_exit(void)
>> {
>> iwl_opmode_deregister("iwlmvm");
>> iwl_mvm_rate_control_unregister();
>> + kthread_stop(init_thread);
>> }
>> module_exit(iwl_mvm_exit);
>>
>> diff --git a/drivers/net/wireless/iwlwifi/pcie/drv.c b/drivers/net/wireless/iwlwifi/pcie/drv.c
>> index 98950e4..c1f2823 100644
>> --- a/drivers/net/wireless/iwlwifi/pcie/drv.c
>> +++ b/drivers/net/wireless/iwlwifi/pcie/drv.c
>> @@ -489,6 +489,10 @@ static int iwl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>> struct iwl_trans_pcie *trans_pcie;
>> int ret;
>>
>> + printk("iwlwifi Going to sleep for 33 seconds\n");
>> + ssleep(33);
>> + printk("iwlwifi Done sleeping\n");
>> +
>> iwl_trans = iwl_trans_pcie_alloc(pdev, ent, cfg);
>> if (IS_ERR(iwl_trans))
>> return PTR_ERR(iwl_trans);
>>
>
> I guess that the problem is that you moved the init stuff into kthread
> for iwlmvm module, but the stall happens in a different module,
> iwlwifi. So iwlwifi is killed as expected. You had to put the
> kthread hack into pcie/drv.c instead.

Indeed, will work on a general solution next, thanks!

> (Actually, it's interesting how the SIGKILL error is reported back;
> it failed at request_threaded_irq(). If this were the normal irq
> handler, it might have worked :)

:)

Luis