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: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 0 insertions, 6 deletions

diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index aea0d438e3c7..c8f81da15c7e 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -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 */
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 5a75d23645c8..5eae53b1e306 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -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:
          */