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    SubjectRe: [PATCH] use mutex instead of semaphore in tty_io.c
    El Thu, May 31, 2007 at 03:37:12PM -0700 Andrew Morton ha dit:

    > On Thu, 31 May 2007 15:42:26 +0200
    > Matthias Kaehlcke <matthias.kaehlcke@gmail.com> wrote:
    >
    > > drivers/char/tty_io.c: Use spinlock instead of a (binary) semaphore
    > >
    >
    > hm.
    >
    > >
    >
    > We end up with this:
    >
    > /* find a device that is not in use. */
    > if (!idr_pre_get(&allocated_ptys, GFP_KERNEL))
    > return -ENOMEM;
    >
    > spin_lock(&allocated_ptys_lock);
    >
    > idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
    > if (idr_ret < 0) {
    > spin_unlock(&allocated_ptys_lock);
    > if (idr_ret == -EAGAIN)
    > return -ENOMEM;
    > return -EIO;
    > }
    > if (index >= pty_limit) {
    > idr_remove(&allocated_ptys, index);
    > spin_unlock(&allocated_ptys_lock);
    > return -EIO;
    > }
    > spin_unlock(&allocated_ptys_lock);
    >
    > this leaves a small window in which another thread can come in and steal
    > away the idr tree's reserves, causing the idr_get_new() to fail. It's
    > highly improbable, but it's real.

    i agree, thanks for pointing it out

    > Hence I think a straight semaphore->mutex conversion would be better.

    that leads us back to the initial patch. christoph: is that ok for
    you or do you have another proposal?

    --
    Matthias Kaehlcke
    Linux Application Developer
    Barcelona

    The assumption that what currently exists must necessarily
    exist is the acid that corrodes all visionary thinking
    .''`.
    using free software / Debian GNU/Linux | http://debian.org : :' :
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