Commit 36d883ba authored by Anthony PERARD's avatar Anthony PERARD Committed by Max Reitz
Browse files

xen-block: Fix double qlist remove and request leak 



Commit a31ca680 ("qemu/queue.h: clear linked list pointers on
remove") revealed that a request was removed twice from a list, once
in xen_block_finish_request() and a second time in
xen_block_release_request() when both function are called from
xen_block_complete_aio(). But also, the `requests_inflight' counter is
decreased twice, and thus became negative.

This is a bug that was introduced in bfd0d636 ("xen-block: improve
response latency"), where a `finished' list was removed.

That commit also introduced a leak of request in xen_block_do_aio().
That function calls xen_block_finish_request() but the request is
never released after that.

To fix both issue, we do two changes:
- we squash finish_request() and release_request() together as we want
  to remove a request from 'inflight' list to add it to 'freelist'.
- before releasing a request, we need to let the other end know the
  result, thus we should call xen_block_send_response() before
  releasing a request.

The first change fixes the double QLIST_REMOVE() as we remove the extra
call. The second change makes the leak go away because if we want to
call finish_request(), we need to call a function that does all of
finish, send response, and release.

Fixes: bfd0d636 ("xen-block: improve response latency")
Signed-off-by: default avatarAnthony PERARD <anthony.perard@citrix.com>
Message-Id: <20200406140217.1441858-1-anthony.perard@citrix.com>
Reviewed-by: default avatarPaul Durrant <paul@xen.org>
[mreitz: Amended commit message as per Paul's suggestions]
Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
parent 25fb2e9c

hw/block/dataplane/xen-block.c

+16 −32
Original line number Diff line number Diff line
@@ -64,6 +64,8 @@ struct XenBlockDataPlane { 
    AioContext *ctx;

};



static int xen_block_send_response(XenBlockRequest *request);



static void reset_request(XenBlockRequest *request)

{

    memset(&request->req, 0, sizeof(request->req));
@@ -115,23 +117,26 @@ out: 
    return request;

}



static void xen_block_finish_request(XenBlockRequest *request)

static void xen_block_complete_request(XenBlockRequest *request)

{

    XenBlockDataPlane *dataplane = request->dataplane;



    QLIST_REMOVE(request, list);

    dataplane->requests_inflight--;

}

    if (xen_block_send_response(request)) {

        Error *local_err = NULL;



static void xen_block_release_request(XenBlockRequest *request)

{

    XenBlockDataPlane *dataplane = request->dataplane;

        xen_device_notify_event_channel(dataplane->xendev,

                                        dataplane->event_channel,

                                        &local_err);

        if (local_err) {

            error_report_err(local_err);

        }

    }



    QLIST_REMOVE(request, list);

    dataplane->requests_inflight--;

    reset_request(request);

    request->dataplane = dataplane;

    QLIST_INSERT_HEAD(&dataplane->freelist, request, list);

    dataplane->requests_inflight--;

}



/*
@@ -246,7 +251,6 @@ static int xen_block_copy_request(XenBlockRequest *request) 
}



static int xen_block_do_aio(XenBlockRequest *request);

static int xen_block_send_response(XenBlockRequest *request);



static void xen_block_complete_aio(void *opaque, int ret)

{
@@ -286,7 +290,6 @@ static void xen_block_complete_aio(void *opaque, int ret) 
    }



    request->status = request->aio_errors ? BLKIF_RSP_ERROR : BLKIF_RSP_OKAY;

    xen_block_finish_request(request);



    switch (request->req.operation) {

    case BLKIF_OP_WRITE:
@@ -306,17 +309,8 @@ static void xen_block_complete_aio(void *opaque, int ret) 
    default:

        break;

    }

    if (xen_block_send_response(request)) {

        Error *local_err = NULL;



        xen_device_notify_event_channel(dataplane->xendev,

                                        dataplane->event_channel,

                                        &local_err);

        if (local_err) {

            error_report_err(local_err);

        }

    }

    xen_block_release_request(request);

    xen_block_complete_request(request);



    if (dataplane->more_work) {

        qemu_bh_schedule(dataplane->bh);
@@ -420,8 +414,8 @@ static int xen_block_do_aio(XenBlockRequest *request) 
    return 0;



err:

    xen_block_finish_request(request);

    request->status = BLKIF_RSP_ERROR;

    xen_block_complete_request(request);

    return -1;

}
@@ -575,17 +569,7 @@ static bool xen_block_handle_requests(XenBlockDataPlane *dataplane) 
                break;

            };



            if (xen_block_send_response(request)) {

                Error *local_err = NULL;



                xen_device_notify_event_channel(dataplane->xendev,

                                                dataplane->event_channel,

                                                &local_err);

                if (local_err) {

                    error_report_err(local_err);

                }

            }

            xen_block_release_request(request);

            xen_block_complete_request(request);

            continue;

        }