Trond Myklebust wrote:
On Sun, 2009-01-04 at 14:12 -0500, Trond Myklebust wrote:
On Fri, 2009-01-02 at 15:44 -0600, Tom Tucker wrote:
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@xxxxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxx>
---
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;
I see nothing that stops svc_delete_xprt() from setting XPT_DEAD after
the above test in svc_revisit(), and before the test inside
svc_xprt_enqueue(). What's preventing a race there?
I suppose one way to fix it would be to hold the xprt->xpt_lock across
the above test, and to make sure that you set XPT_DEFERRED while holding
the lock, and _before_ you test for XPT_DEAD. That way, you guarantee
that the svc_deferred_dequeue() loop in svc_delete_xprt() will pick up
anything that races with the setting of XPT_DEAD.
Yes, see previous post. Thanks Trond.
Trond
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