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    SubjectRe: [linux-pm] Freezer: Don't count threads waiting for frozen filesystems.
    Date
    On Monday, 27 of October 2008, Nigel Cunningham wrote:
    > Hi Miklos.
    >
    > On Mon, 2008-10-27 at 12:12 +0100, Miklos Szeredi wrote:
    > > On Sun, 26 Oct 2008, Rafael J. Wysocki wrote:
    > > > On Saturday, 25 of October 2008, Nigel Cunningham wrote:
    > > > > While working on freezing fuse filesystems, I found that if a filesystem
    > > > > is frozen when we try to freeze processes, freezing can fail because
    > > > > threads are waiting in vfs_check_frozen for the filesystem to be thawed.
    > > > > We should thus not count such threads.
    > > > >
    > > > > The check will be safe if a filesystem is thawed while we're freezing
    > > > > processes because filesystem thaws are only invoked from userspace. Any
    > > > > waiting processes will be woken and frozen prior to us completing the
    > > > > freezing of userspace (the caller invoking the filesystem thaw will be
    > > > > freezing) or - in the worst case - together with kernel threads.
    > >
    > > The description is missing some details: why is the filesystem frozen
    > > before suspend? AFAICS this can happen when DM calls bdev_freeze() on
    > > the device before the task freezing begins. Is this the case?
    >
    > It doesn't matter why a process is sitting in that wait_event call. What
    > does matter is that one can be there. In the case where I saw it, I was
    > working on fuse freezing. I don't remember the details, as it's a year
    > since I made this patch, but I don't think I wasn't using fuse or DM.
    >
    > > Also, while the patch might solve some of the symptoms of the fuse
    > > vs. process freezer interaction, it will not fully fix that problem.
    > > As such it's just a hack to hide the problem, making it less likely to
    > > appear.
    >
    > No, it's part of the solution. I haven't posted the full fuse freezing
    > patch because I thought this could be profitably merged without the rest
    > of the patch.

    Well, I guess it's better if you post the entire thing so that we can see
    what the role of the $subject patch is in it, even if this patch finally gets
    merged separately.

    Thanks,
    Rafael


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