[Pm-utils] lockfile creation not really atomic in pm-utils

[Victor Lowther]

Or move the lock directory to a location that is (or should be
auto-cleaned), like /tmp, or just clean it ourselves with a boot-time
init script.

Using PID values seems like a waste of time if you are using them to
detect stale lockfiles over reboots -- the presence or absence of a
given PID is meaningless in that case.

If there is a case in which suspend/resume fails, the system does not
reboot (or hang and get rebooted), and the lock directory does not get
removed, then that is a fault in the pm-utils scripting that needs
fixed (imao).

On Jan 4, 2008 3:40 PM, Till Maas <opensource at till.name> wrote:
>
> On Fr Januar 4 2008, Victor Lowther wrote:
> > While browsing through the source of pm-utils, I noticed that the
> > lock/unlocking functions were using file creation/removal and PID
> > checking for locking purposes.  In a shell scripting language,
> > however, there is no way to atomically create files.
> >
> > Directory creation, however, is atomic.  Here is a patch to atomicize
> > the lock/unlick functions.
>
> You are so cool, there is a bug about this in Red Hat Bugzilla for Fedora and
> I did not know how to fix it. You seem to be the man. But there is one
> problem with your patch left, though. Now a stale lock directory is not
> removed, e.g. when it was left because a suspend failed and one needed to
> reset the computer. Do you know the best solution for this, too?
>
> I guess adding a second lock directory may help here:
>
> mkdir /.suspended
> - on success: continue, store PID in /.suspended/pid
> - on failure:
> mkdir /.suspended/cleanup
> - on failure: quit
> - on sucess: check pid in /.suspended/pid
>      - process still running: remove /.suspended/cleanup and quit
>      - else: store own pid in /.suspended/pid
>        remove /.suspended/cleanup
>        continue
>
> Regards,
> Till
>
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