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author | Christophe Saout <christophe@saout.de> | 2006-11-05 17:42:48 (GMT) |
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committer | Trond Myklebust <Trond.Myklebust@netapp.com> | 2006-12-06 15:46:24 (GMT) |
commit | cc4dc59e5580d6c0de1685a25b74d32175f43434 (patch) | |
tree | 61de2e40ba38b93027124d691308fc4405ef35d2 | |
parent | ec0bf39a471bf6fcd01def2bd677128cea940b73 (diff) | |
download | linux-fsl-qoriq-cc4dc59e5580d6c0de1685a25b74d32175f43434.tar.xz |
Subject: Re: [PATCH] Fix SUNRPC wakeup/execute race condition
The sunrpc scheduler contains a race condition that can let an RPC
task end up being neither running nor on any wait queue. The race takes
place between rpc_make_runnable (called from rpc_wake_up_task) and
__rpc_execute under the following condition:
First __rpc_execute calls tk_action which puts the task on some wait
queue. The task is dequeued by another process before __rpc_execute
continues its execution. While executing rpc_make_runnable exactly after
setting the task `running' bit and before clearing the `queued' bit
__rpc_execute picks up execution, clears `running' and subsequently
both functions fall through, both under the false assumption somebody
else took the job.
Swapping rpc_test_and_set_running with rpc_clear_queued in
rpc_make_runnable fixes that hole. This introduces another possible
race condition that can be handled by checking for `queued' after
setting the `running' bit.
Bug noticed on a 4-way x86_64 system under XEN with an NFSv4 server
on the same physical machine, apparently one of the few ways to hit
this race condition at all.
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Christophe Saout <christophe@saout.de>
Signed-off-by: Trond Myklebust <trond.myklebust@fys.uio.no>
-rw-r--r-- | net/sunrpc/sched.c | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index a1ab4ee..b57d406 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -295,13 +295,15 @@ EXPORT_SYMBOL(__rpc_wait_for_completion_task); */ static void rpc_make_runnable(struct rpc_task *task) { - int do_ret; - BUG_ON(task->tk_timeout_fn); - do_ret = rpc_test_and_set_running(task); rpc_clear_queued(task); - if (do_ret) + if (rpc_test_and_set_running(task)) + return; + /* We might have raced */ + if (RPC_IS_QUEUED(task)) { + rpc_clear_running(task); return; + } if (RPC_IS_ASYNC(task)) { int status; |