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

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Message-Id: <20140730.151107.1328294951387764830.davem@davemloft.net>
Date:	Wed, 30 Jul 2014 15:11:07 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mcgrof@...not-panic.com
Cc:	gregkh@...uxfoundation.org, tiwai@...e.de,
	linux-kernel@...r.kernel.org, mcgrof@...e.com,
	penguin-kernel@...ove.SAKURA.ne.jp, joseph.salisbury@...onical.com,
	kay@...y.org, gnomes@...rguk.ukuu.org.uk,
	tim.gardner@...onical.com, pierre-fersing@...rref.org,
	akpm@...ux-foundation.org, oleg@...hat.com, bpoirier@...e.de,
	nagalakshmi.nandigama@...gotech.com,
	praveen.krishnamoorthy@...gotech.com,
	sreekanth.reddy@...gotech.com, abhijit.mahajan@...gotech.com,
	hariprasad@...lsio.com, santosh@...lsio.com,
	MPT-FusionLinux.pdl@...gotech.com, linux-scsi@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2 2/4] driver core: enable drivers to use deferred
 probe from init

From: "Luis R. Rodriguez" <mcgrof@...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.

Thanks.
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