On Thu, 2013-01-03 at 18:11 -0500, Trond Myklebust wrote:
> On Thu, 2013-01-03 at 17:26 -0500, Tejun Heo wrote:
> > Ooh, BTW, there was a bug where workqueue code created a false
> > dependency between two work items. 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. A patch is queued to make such occurrences less
> > likely (work functions should also match for two work items considered
> > the same), but if you're seeing this, the best thing to do is freeing
> > the work item at the end of the work function.
>
> That's interesting... I wonder if we may have been hitting that issue.
>
> From what I can see, we do actually free the write RPC task (and hence
> the work_struct) before we call the asynchronous unlink completion...
>
> Dros, can you see if reverting commit
> 324d003b0cd82151adbaecefef57b73f7959a469 + commit
> 168e4b39d1afb79a7e3ea6c3bb246b4c82c6bdb9 and then applying the attached
> patch also fixes the hang on a pristine 3.7.x kernel?
Actually, we probably also need to look at rpc_free_task, so the
following patch, instead...
--
Trond Myklebust
Linux NFS client maintainer
NetApp
[email protected]
www.netapp.com
diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index b6bdb18..400f7ec 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -91,12 +91,13 @@ void nfs_readdata_release(struct nfs_read_data *rdata)
put_nfs_open_context(rdata->args.context);
if (rdata->pages.pagevec != rdata->pages.page_array)
kfree(rdata->pages.pagevec);
- if (rdata != &read_header->rpc_data)
- kfree(rdata);
- else
+ if (rdata == &read_header->rpc_data) {
rdata->header = NULL;
+ rdata = NULL;
+ }
if (atomic_dec_and_test(&hdr->refcnt))
hdr->completion_ops->completion(hdr);
+ kfree(rdata);
}
EXPORT_SYMBOL_GPL(nfs_readdata_release);
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index b673be3..45d9250 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -126,12 +126,13 @@ void nfs_writedata_release(struct nfs_write_data *wdata)
put_nfs_open_context(wdata->args.context);
if (wdata->pages.pagevec != wdata->pages.page_array)
kfree(wdata->pages.pagevec);
- if (wdata != &write_header->rpc_data)
- kfree(wdata);
- else
+ if (wdata == &write_header->rpc_data) {
wdata->header = NULL;
+ wdata = NULL;
+ }
if (atomic_dec_and_test(&hdr->refcnt))
hdr->completion_ops->completion(hdr);
+ kfree(wdata);
}
EXPORT_SYMBOL_GPL(nfs_writedata_release);
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index d17a704..500407a 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -936,14 +936,13 @@ struct rpc_task *rpc_new_task(const struct rpc_task_setup *setup_data)
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)
