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    Subject[ 033/171] SUNRPC: Ensure that we free the rpc_task after cleanups are done
    Date
    3.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Trond Myklebust <Trond.Myklebust@netapp.com>

    commit c6567ed1402c55e19b012e66a8398baec2a726f3 upstream.

    This patch ensures that we free the rpc_task after the cleanup callbacks
    are done in order to avoid a deadlock problem that can be triggered if
    the callback needs to wait for another workqueue item to complete.

    Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
    Cc: Weston Andros Adamson <dros@netapp.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Bruce Fields <bfields@fieldses.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/sunrpc/sched.c | 27 +++++++++++++++++++++++----
    1 file changed, 23 insertions(+), 4 deletions(-)

    --- a/net/sunrpc/sched.c
    +++ b/net/sunrpc/sched.c
    @@ -915,16 +915,35 @@ struct rpc_task *rpc_new_task(const stru
    return task;
    }

    +/*
    + * rpc_free_task - release rpc task and perform cleanups
    + *
    + * Note that we free up the rpc_task _after_ rpc_release_calldata()
    + * in order to work around a workqueue dependency issue.
    + *
    + * Tejun Heo states:
    + * "Workqueue currently considers two work items to be the same if they're
    + * on the same address and won't execute them concurrently - ie. it
    + * makes a work item which is queued again while being executed wait
    + * for the previous execution to complete.
    + *
    + * If a work function frees the work item, and then waits for an event
    + * which should be performed by another work item and *that* work item
    + * recycles the freed work item, it can create a false dependency loop.
    + * There really is no reliable way to detect this short of verifying
    + * every memory free."
    + *
    + */
    static void rpc_free_task(struct rpc_task *task)
    {
    - const struct rpc_call_ops *tk_ops = task->tk_ops;
    - void *calldata = task->tk_calldata;
    + unsigned short tk_flags = task->tk_flags;

    - if (task->tk_flags & RPC_TASK_DYNAMIC) {
    + rpc_release_calldata(task->tk_ops, task->tk_calldata);
    +
    + if (tk_flags & RPC_TASK_DYNAMIC) {
    dprintk("RPC: %5u freeing task\n", task->tk_pid);
    mempool_free(task, rpc_task_mempool);
    }
    - rpc_release_calldata(tk_ops, calldata);
    }

    static void rpc_async_release(struct work_struct *work)



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