On Mon, Jan 07, 2013 at 07:50:10PM +0000, Myklebust, Trond wrote:
> Hi Chris,
>
> Excellent sleuthing! Given the thoroughness of your explanation, I'm
> pretty sure that the attached patch should fix the problem.
>
> Cheers
> Trond
> --
> Trond Myklebust
> Linux NFS client maintainer
>
> NetApp
> Trond.Myklebust@xxxxxxxxxx
> www.netapp.com
> From ec8cbb4aff21cd0eac2c6f3fc4273ac72cdd91ef Mon Sep 17 00:00:00 2001
> From: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
> Date: Mon, 7 Jan 2013 14:30:46 -0500
> Subject: [PATCH] SUNRPC: Ensure we release the socket write lock if the
> rpc_task exits early
>
> If the rpc_task exits while holding the socket write lock before it has
> allocated an rpc slot, then the usual mechanism for releasing the write
> lock in xprt_release() is defeated.
>
> The problem occurs if the call to xprt_lock_write() initially fails, so
> that the rpc_task is put on the xprt->sending wait queue. If the task
> exits after being assigned the lock by __xprt_lock_write_func, but
> before it has retried the call to xprt_lock_and_alloc_slot(), then
> it calls xprt_release() while holding the write lock, but will
> immediately exit due to the test for task->tk_rqstp != NULL.
>
> Reported-by: Chris Perl <chris.perl@xxxxxxxxx>
> Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx [>= 3.1]
> ---
> net/sunrpc/xprt.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index bd462a5..6676457 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -1136,10 +1136,12 @@ static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
> void xprt_release(struct rpc_task *task)
> {
> struct rpc_xprt *xprt;
> - struct rpc_rqst *req;
> + struct rpc_rqst *req = task->tk_rqstp;
>
> - if (!(req = task->tk_rqstp))
> + if (req == NULL) {
> + xprt_release_write(task->tk_xprt, task);
> return;
> + }
>
> xprt = req->rq_xprt;
> if (task->tk_ops->rpc_count_stats != NULL)
> --
> 1.7.11.7
>
Ah, I totally missed the call to `rpc_release_task' at the bottom of the
`__rpc_execute' loop (at least thats how I think we'd get to this function
you're patching).
But wouldn't we need to update the call site in
`rpc_release_resources_task' as well? It contains an explicit check for
`task->tk_rqstp' being non null.
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