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SUNRPC: Ensure that we free the rpc_task after cleanups are done 

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>
Cc: stable@vger.kernel.org
This commit is contained in:
Trond Myklebust 2013-01-04 12:23:21 -05:00
parent e25fbe380c
commit c6567ed140
1 changed files with 23 additions and 4 deletions
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27
net/sunrpc/sched.c
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@ -934,16 +934,35 @@ struct rpc_task *rpc_new_task(const struct rpc_task_setup *setup_data)
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)