lk/linux-kernel-test
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

SUNRPC: Close a race in __rpc_wait_for_completion_task()

Browse Source 
Although they run as rpciod background tasks, under normal operation
(i.e. no SIGKILL), functions like nfs_sillyrename(), nfs4_proc_unlck()
and nfs4_do_close() want to be fully synchronous. This means that when we
exit, we want all references to the rpc_task to be gone, and we want
any dentry references etc. held by that task to be released.

For this reason these functions call __rpc_wait_for_completion_task(),
followed by rpc_put_task() in the expectation that the latter will be
releasing the last reference to the rpc_task, and thus ensuring that the
callback_ops->rpc_release() has been called synchronously.

This patch fixes a race which exists due to the fact that
rpciod calls rpc_complete_task() (in order to wake up the callers of
__rpc_wait_for_completion_task()) and then subsequently calls
rpc_put_task() without ensuring that these two steps are done atomically.

In order to avoid adding new spin locks, the patch uses the existing
waitqueue spin lock to order the rpc_task reference count releases between
the waiting process and rpciod.
The common case where nobody is waiting for completion is optimised for by
checking if the RPC_TASK_ASYNC flag is cleared and/or if the rpc_task
reference count is 1: in those cases we drop trying to grab the spin lock,
and immediately free up the rpc_task.

Those few processes that need to put the rpc_task from inside an
asynchronous context and that do not care about ordering are given a new
helper: rpc_put_task_async().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Trond Myklebust
2011-02-21 11:05:41 -08:00
parent 214d93b02c
commit bf294b41ce
5 changed files with 66 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
fs/nfs/nfs4proc.c
View File

@@ -4150,7 +4150,7 @@ static void nfs4_lock_release(void *calldata)
task = nfs4_do_unlck(&data->fl, data->ctx, data->lsp,
data->arg.lock_seqid);
if (!IS_ERR(task))
rpc_put_task(task);
rpc_put_task_async(task);
dprintk("%s: cancelling lock!\n", __func__);
} else
nfs_free_seqid(data->arg.lock_seqid);
@@ -5227,7 +5227,7 @@ static int nfs41_proc_async_sequence(struct nfs_client *clp, struct rpc_cred *cr
if (IS_ERR(task))
ret = PTR_ERR(task);
else
rpc_put_task(task);
rpc_put_task_async(task);
dprintk("<-- %s status=%d\n", __func__, ret);
return ret;
}