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SubjectRe: 2.2.18/swsusp bugs
"PM" == Pavel Machek <pavel@suse.cz> writes:

PM> Well, global entries are for things common to all processes, like
PM> vmalloced area. But you are just booting different kernel, which has
PM> different vmalloced areas.

You're right, of course. We're replacing all page tables by then.

PM> So what happens is * kernel works, prepares some work into the journal *
PM> suspend/resume cycle, work in journal is actually done * kernel might be
PM> pretty confused here, as its disk state changed below it...
>> The kernel isn't confused, is just unaware that it just writes again the
>> state that's in fact (well, supposedly) already on disk.

PM> I'm not sure this is safe.

I didn't say I was sure either, but it is supposed to, I believe.

>> That can probably be done by going over all disk drivers and
>> understanding how they guarantee all (DMA) transactions are over.

PM> Yep. That's what I'm going to do.

I was hoping there was something higher-level that had that info available...

>> Alright, but provided that trying to resume from a non-suspend swap
>> doesn't crash anything...

PM> Do you stop all user processes before doing resume, for example?

(Different subject, hey?-). No, I don't. At the point I do (and recommend to)
swapon is during early init processing. There are no user processes at that
point. If they are, they disappear in thin air at that point...

But I already gave up, I agree w/your method. But remember that people will
boot resume=/bla even when they have no swap to resume from. Just a lilo thing,
unavoidable.

PM> But that might be problem at resume. Imagine uhci has buffers at
PM> 0x12345678, but in image being resumed, /bin/bash is at 0x12345678. Then
PM> you have a problem.

Nope, that can't happen. uhci and bash had their pages neatly restored...
Wait! Are you saying you start uhci/netdrivers/enable interrupts BEFORE
resuming?? Nonono! Forbidden! Disk corruption, or your computer may explode!

(Apart from the explosions, all that seems to routinely happen in swsusp-2.4 ;-)

>> How about disabling interrupts except for the swap disk driver? Just a
>> thought...

PM> You don't easily know which one is it.

Why? You have the major/minor! (Remember you got the user to tell you).
Looks easy from here (I'm not looking at the code right now :-)

PM> [swsusp list no longer works, doing cc to l-k.]

So it seems. It didn't bounce yesterday, but didn't get a response. OTOH, l-k
isn't too busy a place to discuss swsusp? How about the ACPI list?

(BTW, I'm not subscribed to l-k. But I can read the archives...)

--
Jose' Pereira (CIIST sysadm) Tel. +351.21.841 7526
Centro de Informatica
Instituto Superior Tecnico - Technical University of Lisboa
Av. Rovisco Pais - 1049-001 Lisboa - Portugal
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