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    SubjectRe: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway
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    > > > > And teach VFS to block suspension, while waiting on a mutex held by
    > > > > another process performing a fuse operation.
    > > > >
    > > > > I can already hear the beautiful praise from Al Viro at the sight of
    > > > > that ;)
    > > >
    > > > There is that.
    > > >
    > > > OK, bite the bullet. Tasks involved in fuse are special. Give them a flag
    > > > and teach the freezer to put them on ice only after all other task are
    > > > frozen. In a way they are kernel, there's no use denying that.
    > >
    > > And flag every other process, that the flagged process is
    > > communicating with? How are you proposing to do that?
    > >
    > > Quoting Paul:
    > >
    > > "1. The freezer cannot be guaranteed deadlock-free without constructing
    > > a dependency graph between tasks (both user and kernel), which is
    > > virtually impossible since the dependencies are not externally
    > > observable."
    >
    > A deadlock requires that the circular wait is uninterruptible. Normal IPC
    > isn't.
    >
    > What are you doing in the userland portions of fuse? Some kind of IPC
    > with other tasks?

    Anything, writing to a file, writing to shared memory, sending things
    over the network. There's no limit to what a filesystem daemon may
    do. It's a perfectly ordinary unprivileged userspace process. And
    this is a feature not a bug.

    > There is a limit to which you can push kernel functionality into
    > user space.

    Limiting what a userspace filesystem can do would defeat the whole
    purpose of the bloody thing. This is not negotiable ;)

    Miklos
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