Re: [PATCH 3/3] SUNRPC: svc_xprt_enqueue should not refuse to enqueue 'XPT_DEAD' transports

Tom Tucker
2009-01-02T21:44:21Z

Bruce/Trond:

This is an alternative to patches 2 and 3 from Trond's fix. I think
Trond's fix is correct, but I believe this approach to be simpler.

From: Tom Tucker <tom@opengridcomputing.com>
Date: Wed, 31 Dec 2008 17:18:33 -0600
Subject: [PATCH] svc: Clean up deferred requests on transport destruction

A race between svc_revisit and svc_delete_xprt can result in
deferred requests holding references on a transport that can never be
recovered because dead transports are not enqueued for subsequent
processing.

Check for XPT_DEAD in revisit to clean up completing deferrals on a dead
transport and sweep a transport's deferred queue to do the same for queued
but unprocessed deferrals.

Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
---
net/sunrpc/svc_xprt.c | 20 +++++++++++++++-----
1 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index bf5b5cd..92ca5c6 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -837,6 +837,11 @@ static void svc_age_temp_xprts(unsigned long closure)
void svc_delete_xprt(struct svc_xprt *xprt)
{
struct svc_serv *serv = xprt->xpt_server;
+ struct svc_deferred_req *dr;
+
+ /* Only do this once */
+ if (test_and_set_bit(XPT_DEAD, &xprt->xpt_flags))
+ return;

dprintk("svc: svc_delete_xprt(%p)\n", xprt);
xprt->xpt_ops->xpo_detach(xprt);
@@ -851,12 +856,16 @@ void svc_delete_xprt(struct svc_xprt *xprt)
* while still attached to a queue, the queue itself
* is about to be destroyed (in svc_destroy).
*/
- if (!test_and_set_bit(XPT_DEAD, &xprt->xpt_flags)) {
- BUG_ON(atomic_read(&xprt->xpt_ref.refcount) < 2);
- if (test_bit(XPT_TEMP, &xprt->xpt_flags))
- serv->sv_tmpcnt--;
+ if (test_bit(XPT_TEMP, &xprt->xpt_flags))
+ serv->sv_tmpcnt--;
+
+ for (dr = svc_deferred_dequeue(xprt); dr;
+ dr = svc_deferred_dequeue(xprt)) {
svc_xprt_put(xprt);
+ kfree(dr);
}
+
+ svc_xprt_put(xprt);
spin_unlock_bh(&serv->sv_lock);
}

@@ -902,7 +911,8 @@ static void svc_revisit(struct cache_deferred_req *dreq, int too_many)
container_of(dreq, struct svc_deferred_req, handle);
struct svc_xprt *xprt = dr->xprt;

- if (too_many) {
+ if (too_many || test_bit(XPT_DEAD, &xprt->xpt_flags)) {
+ dprintk("revisit cancelled\n");
svc_xprt_put(xprt);
kfree(dr);
return;