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authorTrond Myklebust <Trond.Myklebust@netapp.com>2011-02-21 11:05:41 -0800
committerTrond Myklebust <Trond.Myklebust@netapp.com>2011-03-10 15:04:52 -0500
commitbf294b41cefcb22fc3139e0f42c5b3f06728bd5e (patch)
tree250251c040a2d2e278b5a2ddd03c8d20a27be129 /fs
parent214d93b02c4fe93638ad268613c9702a81ed9192 (diff)
downloadlinux-linaro-stable-bf294b41cefcb22fc3139e0f42c5b3f06728bd5e.tar.gz
SUNRPC: Close a race in __rpc_wait_for_completion_task()
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>
Diffstat (limited to 'fs')
-rw-r--r--fs/nfs/nfs4proc.c4
-rw-r--r--fs/nfs/unlink.c2
2 files changed, 3 insertions, 3 deletions
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 1ff76acc7e98..d1ed67145cf3 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -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;
}
diff --git a/fs/nfs/unlink.c b/fs/nfs/unlink.c
index e313a51acdd1..6481d537d69d 100644
--- a/fs/nfs/unlink.c
+++ b/fs/nfs/unlink.c
@@ -180,7 +180,7 @@ static int nfs_do_call_unlink(struct dentry *parent, struct inode *dir, struct n
task_setup_data.rpc_client = NFS_CLIENT(dir);
task = rpc_run_task(&task_setup_data);
if (!IS_ERR(task))
- rpc_put_task(task);
+ rpc_put_task_async(task);
return 1;
}