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RPC: killing RPC tasks races fixed

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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 <skinsbursky@openvz.org>
Cc: stable@kernel.org
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Stanislav Kinsbursky 2011-03-17 18:54:23 +03:00 committed by Trond Myklebust
parent ba3c578de2
commit 8e26de238f
1 changed files with 3 additions and 1 deletions
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4
net/sunrpc/clnt.c
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@ -436,7 +436,9 @@ void rpc_killall_tasks(struct rpc_clnt *clnt)
if (!(rovr->tk_flags & RPC_TASK_KILLED)) { if (!(rovr->tk_flags & RPC_TASK_KILLED)) {
rovr->tk_flags |= RPC_TASK_KILLED; rovr->tk_flags |= RPC_TASK_KILLED;
rpc_exit(rovr, -EIO); 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); spin_unlock(&clnt->cl_lock);