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Date: Sun, 20 Jul 2008 09:23:31 +0200 From: Rene Herman <rene.herman@...access.nl> To: Arjan van de Ven <arjan@...radead.org> CC: linux-kernel@...r.kernel.org, mingo@...e.hu, Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl> Subject: Re: [patch 1/3] fastboot: Create a "asynchronous" initlevel On 19-07-08 17:44, Arjan van de Ven wrote: > On Sat, 19 Jul 2008 10:10:09 +0200 > Rene Herman <rene.herman@...access.nl> wrote: >>> I'm not sure about this comment, being not very sure about the >>> semantics of late_initcall but shouldn't late_initcall (level 7) >>> wait for 6s to have completed? >> >> Following up on this myself -- see for example kernel/power/disk.c: >> power_suspend(). It's a late intitcall so that, as it comments, >> "all devices are discovered and initialized". However, your first >> followup patch makes the USB HCI init async meaning that any USB >> storage device might not be ready yet when it runs, no? > > good spotting/comment. > > you would have a valid point... if it weren't for the case where much > of this actual "end device" probing is in various cases already > asynchronous... what you do have found is a bug in the suspend code. > Unless code does: > /* wait for the known devices to complete their probing */ > while (driver_probe_done() != 0) > msleep(100); > (taken from init/do_mounts.c) > > ... the assertion in the comment that probing is done is absolutely > false, with or without my patches. Yes, I see. Unfortunately, WITH your patches, driver_probe_done() would also no longer be safe when run from a late_initcall() it would appear. driver_probe_done() tests a variable that's incremented just before the driver model calls into the driver .probe method and decremented on return from it (really_probe). However, if the entire module_init() is async the probing may not even have _started_ yet let alone finished. Let's take ehci_hcd_init() as an example both since you changed that one and since it'll fairly often be en route to mass storage devices. Only after ehci_init() calls foo_register_driver() is the driver model aware of it and will it start calling the probe methods meaning the driver_probe_done() would be racing. I have the sneaking suspicion that this is a bit of a fundamental issue. Turning some of the driver level (6) async basicaly removes the ordering between drivers and late_initcall (level 7). I trust it will completely and utterly destroy the point of this patch to flush level 6a before starting level 7? > (Not that I want the suspend/resume code to call this, because that > would make the boot even longer ;( ) Well, yes, but bugs are bugs. CCing Pavel and Rafael as well :-) Rene. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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