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Date: Tue, 15 Apr 2008 06:48:50 +1000 From: Benjamin Herrenschmidt <benh@...nel.crashing.org> To: Alan Stern <stern@...land.harvard.edu> Cc: "Rafael J. Wysocki" <rjw@...k.pl>, Greg KH <greg@...ah.com>, pm list <linux-pm@...ts.linux-foundation.org>, ACPI Devel Maling List <linux-acpi@...r.kernel.org>, Len Brown <lenb@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Alexey Starikovskiy <astarikovskiy@...e.de>, David Brownell <david-b@...bell.net>, Pavel Machek <pavel@....cz>, Oliver Neukum <oliver@...kum.org>, Nigel Cunningham <ncunningham@...a.org.au>, Jesse Barnes <jbarnes@...tuousgeek.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH 1/3] PM: Introduce new top level suspend and hibernation callbacks (rev. 8) On Mon, 2008-04-14 at 11:13 -0400, Alan Stern wrote: > On Mon, 14 Apr 2008, Rafael J. Wysocki wrote: > > > "you can assume that the user space is there while ->prepare() is running, > > but you are supposed to prevent new children of the device from being > > registered from that point on _and_ you have to make sure that freezable > > tasks will be able to freeze after ->prepare() has run" (but why on Earth a > > driver writer is now required to know what's a freezable task etc.?) > > This reminds me... We're going to need a way to make certain > activities mutually exclusive with system sleep. The simplest example > is loading a kernel module; init and probe routines often end up > causing new child devices to be registered. > > The most straightforward approach is to use an rwsem like the one we > used to have. However I'm concerned that under some circumstances > there might be recursive read-locking. (For example, the init routine > in a newly-loaded module decides to load yet another module. Can this > actually happen? libusual does something much like it.) > > So it's quite possible we'll end up needing a mechanism that resembles > an rwsem but allows recursive (properly nested) read-locking. Does > such a thing exist already, or would it have to be invented? Despite what Oliver says, that's a perfect example where the module load syscalls should return an error. Maybe something like -EAGAIN would do tho... that might need a minor update of the module init tools so they retry instead of failing. Ben. -- 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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