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    SubjectRe: DEFINE_IDA causing memory leaks? (was Re: [PATCH 1/2] virtio: fix memory leak of virtio ida cache layers)
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    On Thu, 2015-09-17 at 08:33 +0300, Michael S. Tsirkin wrote:
    > On Wed, Sep 16, 2015 at 07:29:17PM -0500, Suman Anna wrote:
    > > The virtio core uses a static ida named virtio_index_ida for
    > > assigning index numbers to virtio devices during registration.
    > > The ida core may allocate some internal idr cache layers and
    > > an ida bitmap upon any ida allocation, and all these layers are
    > > truely freed only upon the ida destruction. The virtio_index_ida
    > > is not destroyed at present, leading to a memory leak when using
    > > the virtio core as a module and atleast one virtio device is
    > > registered and unregistered.
    > >
    > > Fix this by invoking ida_destroy() in the virtio core module
    > > exit.
    > >
    > > Cc: "Michael S. Tsirkin" <mst@redhat.com>
    > > Signed-off-by: Suman Anna <s-anna@ti.com>
    >
    > Interesting.
    > Will the same apply to e.g. sd_index_ida in drivers/scsi/sd.c
    > or iscsi_sess_ida in drivers/scsi/scsi_transport_iscsi.c?
    >
    > If no, why not?
    >
    > One doesn't generally expect to have to free global variables.
    > Maybe we should forbid DEFINE_IDA in modules?
    >
    > James, could you comment on this please?

    ida is Tejun's baby (cc'd). However, it does look like without
    ida_destroy() you will leave a cached ida->bitmap dangling because we're
    trying to be a bit clever in ida_remove() so we cache the bitmap to
    relieve ida_pre_get() of the burden if we would otherwise free it.

    I don't understand why you'd want to forbid DEFINE_IDA ... all it does
    is pre-initialise a usually static ida structure. The initialised
    structure will have a NULL bitmap cache that's allocated in the first
    ida_pre_get() ... that all seems to work as expected and no different
    from a dynamically allocated struct ida. Or are you thinking because
    ida_destory() doesn't set bitmap to NULL, it damages the reuse? In
    which case I'm not sure there's much benefit to making it reusable, but
    I suppose we could by adding a memset into ida_destroy().

    James

    > > ---
    > > drivers/virtio/virtio.c | 1 +
    > > 1 file changed, 1 insertion(+)
    > >
    > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
    > > index b1877d73fa56..7062bb0975a5 100644
    > > --- a/drivers/virtio/virtio.c
    > > +++ b/drivers/virtio/virtio.c
    > > @@ -412,6 +412,7 @@ static int virtio_init(void)
    > > static void __exit virtio_exit(void)
    > > {
    > > bus_unregister(&virtio_bus);
    > > + ida_destroy(&virtio_index_ida);
    > > }
    > > core_initcall(virtio_init);
    > > module_exit(virtio_exit);
    > > --
    > > 2.5.0
    > --
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