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author | Trond Myklebust <Trond.Myklebust@netapp.com> | 2011-02-21 22:05:41 +0300 |
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committer | Trond Myklebust <Trond.Myklebust@netapp.com> | 2011-03-10 23:04:52 +0300 |
commit | bf294b41cefcb22fc3139e0f42c5b3f06728bd5e (patch) | |
tree | 250251c040a2d2e278b5a2ddd03c8d20a27be129 /include/linux/sunrpc/sched.h | |
parent | 214d93b02c4fe93638ad268613c9702a81ed9192 (diff) | |
download | linux-bf294b41cefcb22fc3139e0f42c5b3f06728bd5e.tar.xz |
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 'include/linux/sunrpc/sched.h')
-rw-r--r-- | include/linux/sunrpc/sched.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h index 88513fd8e208..d81db8012c63 100644 --- a/include/linux/sunrpc/sched.h +++ b/include/linux/sunrpc/sched.h @@ -212,6 +212,7 @@ struct rpc_task *rpc_run_task(const struct rpc_task_setup *); struct rpc_task *rpc_run_bc_task(struct rpc_rqst *req, const struct rpc_call_ops *ops); void rpc_put_task(struct rpc_task *); +void rpc_put_task_async(struct rpc_task *); void rpc_exit_task(struct rpc_task *); void rpc_exit(struct rpc_task *, int); void rpc_release_calldata(const struct rpc_call_ops *, void *); |