Commit 7c96aef7 authored by NeilBrown's avatar NeilBrown Committed by J. Bruce Fields
Browse files

sunrpc: remove xpt_pool 



The xpt_pool field is only used for reporting BUGs.
And it isn't used correctly.

In particular, when it is cleared in svc_xprt_received before
XPT_BUSY is cleared, there is no guarantee that either the
compiler or the CPU might not re-order to two assignments, just
setting xpt_pool to NULL after XPT_BUSY is cleared.

If a different cpu were running svc_xprt_enqueue at this moment,
it might see XPT_BUSY clear and then xpt_pool non-NULL, and
so BUG.

This could be fixed by calling
  smp_mb__before_clear_bit()
before the clear_bit.  However as xpt_pool isn't really used,
it seems safest to simply remove xpt_pool.

Another alternate would be to change the clear_bit to
clear_bit_unlock, and the test_and_set_bit to test_and_set_bit_lock.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent 18b631f8

include/linux/sunrpc/svc_xprt.h

+0 −1
Original line number Diff line number Diff line
@@ -63,7 +63,6 @@ struct svc_xprt { 
#define XPT_LISTENER	11		/* listening endpoint */

#define XPT_CACHE_AUTH	12		/* cache auth info */



	struct svc_pool		*xpt_pool;	/* current pool iff queued */

	struct svc_serv		*xpt_server;	/* service for transport */

	atomic_t    	    	xpt_reserved;	/* space on outq that is rsvd */

	struct mutex		xpt_mutex;	/* to serialize sending data */

net/sunrpc/svc_xprt.c

+0 −5
Original line number Diff line number Diff line
@@ -351,8 +351,6 @@ void svc_xprt_enqueue(struct svc_xprt *xprt) 
		dprintk("svc: transport %p busy, not enqueued\n", xprt);

		goto out_unlock;

	}

	BUG_ON(xprt->xpt_pool != NULL);

	xprt->xpt_pool = pool;



	if (!list_empty(&pool->sp_threads)) {

		rqstp = list_entry(pool->sp_threads.next,
@@ -370,13 +368,11 @@ void svc_xprt_enqueue(struct svc_xprt *xprt) 
		rqstp->rq_reserved = serv->sv_max_mesg;

		atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);

		pool->sp_stats.threads_woken++;

		BUG_ON(xprt->xpt_pool != pool);

		wake_up(&rqstp->rq_wait);

	} else {

		dprintk("svc: transport %p put into queue\n", xprt);

		list_add_tail(&xprt->xpt_ready, &pool->sp_sockets);

		pool->sp_stats.sockets_queued++;

		BUG_ON(xprt->xpt_pool != pool);

	}



out_unlock:
@@ -415,7 +411,6 @@ static struct svc_xprt *svc_xprt_dequeue(struct svc_pool *pool) 
void svc_xprt_received(struct svc_xprt *xprt)

{

	BUG_ON(!test_bit(XPT_BUSY, &xprt->xpt_flags));

	xprt->xpt_pool = NULL;

	/* As soon as we clear busy, the xprt could be closed and

	 * 'put', so we need a reference to call svc_xprt_enqueue with:

	 */

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