[PATCH v2] RPC: killing RPC tasks races fixed
From: Stanislav Kinsbursky <hidden>
Date: 2011-03-17 15:54:22
Also in:
linux-nfs, lkml
Subsystem:
kernel nfsd, sunrpc, and lockd servers, networking [general], nfs, sunrpc, and lockd clients, the rest · Maintainers:
Chuck Lever, Jeff Layton, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Trond Myklebust, Anna Schumaker, Linus Torvalds
RPC task RPC_TASK_QUEUED bit is set must be checked before trying to wake up task rpc_killall_tasks() because task->tk_waitqueue can not be set (equal to NULL). Also, as Trond Myklebust mentioned, such approach (instead of checking tk_waitqueue to NULL) allows us to "optimise away the call to rpc_wake_up_queued_task() altogether for those tasks that aren't queued". Here is an example of dereferencing of tk_waitqueue equal to NULL: CPU 0 CPU 1 CPU 2 -------------------- --------------------- -------------------------- nfs4_run_open_task rpc_run_task rpc_execute rpc_set_active rpc_make_runnable (waiting) rpc_async_schedule nfs4_open_prepare nfs_wait_on_sequence nfs_umount_begin rpc_killall_tasks rpc_wake_up_task rpc_wake_up_queued_task spin_lock(tk_waitqueue == NULL) BUG() rpc_sleep_on spin_lock(&q->lock) __rpc_sleep_on task->tk_waitqueue = q Signed-off-by: Stanislav Kinsbursky <redacted> --- net/sunrpc/clnt.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-)
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 57d344c..3444757 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c@@ -436,7 +436,9 @@ void rpc_killall_tasks(struct rpc_clnt *clnt) if (!(rovr->tk_flags & RPC_TASK_KILLED)) { rovr->tk_flags |= RPC_TASK_KILLED; rpc_exit(rovr, -EIO); - rpc_wake_up_queued_task(rovr->tk_waitqueue, rovr); + if (RPC_IS_QUEUED(rovr)) + rpc_wake_up_queued_task(rovr->tk_waitqueue, + rovr); } } spin_unlock(&clnt->cl_lock);