linux-kernel - Re: [linux-pm] [PATCH] Remove process freezer from suspend to RAM pathway

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 4 Jul 2007 10:38:47 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Matthew Garrett <mjg59@...f.ucam.org>
cc:	linux-kernel@...r.kernel.org, <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH] Remove process freezer from suspend to RAM
 pathway

On Tue, 3 Jul 2007, Matthew Garrett wrote:

> On Tue, Jul 03, 2007 at 06:21:42PM -0400, Alan Stern wrote:
> > On Tue, 3 Jul 2007, Matthew Garrett wrote:
> > > We're used to the idea of applications blocking when a resource they're 
> > > using goes away - NFS has done it forever. 
> > 
> > You persist in evading my point.  I'm not worried about applications;  
> > I'm worried about drivers.
> > 
> > Let me put it explicitly: You're writing a driver.  You're working on
> > the read, write, or probe method.  You add code to check if a system
> > sleep is underway.  Suppose the answer is Yes -- what does your driver
> > do next?
> 
> Leave the process blocked and defer any i/o until after resume. Why does 
> it need to be any more complicated than that?

(1) The driver will undoubtedly hold some mutex or semaphore at the 
time it checks whether a system sleep is underway.  You will have to 
drop it before blocking and then reacquire it afterward.

(2) The driver may have been called by some other routine which holds a 
mutex needed for resuming the device.  In this case the driver _can't_ 
drop the mutex and so the resume will deadlock.

Okay, I agree that (1) can be handled without too much effort.  But 
doing it adds an extra test to _every_ driver's I/O pathway.  Freezing 
userspace does not incur all this additional overhead.

(2) shouldn't arise during normal read and write operations, but it
certainly _will_ arise during probe.

Alan Stern

-
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/