Re: The recent kref_put warning (was: [PATCH] sunrpc: remove unnecessary svc_xprt_put)

J. Bruce Fields
2010-03-01T03:45:42Z

On Mon, Mar 01, 2010 at 10:57:34AM +1100, Neil Brown wrote:
> No, you are correct. "return 0" is wrong, it should be "return -EAGAIN",
> both in the XPT_CLOSE case and the XPT_LISTENER case.
>
> I observed that in both those cases, 'len' remained at 0 and we didn't do
> much else but 'return len', so I optimised.
> I forgot to factor in:
>
> if (len == 0 || len == -EAGAIN) {
> rqstp->rq_res.len = 0;
> svc_xprt_release(rqstp);
> return -EAGAIN;
> }
>
> So the svc_xprt_release needs to be moved in there as well, I'm not sure
> about the rq_res.len = 0.
> Maybe that was a bad case of premature-optimisation :-)
>
> We should probably leave that last else clause as it is and just have a
> single return from the function.

OK, so the below is what I'm thinking of sending, after some testing;
really just a split-up version of your patches (uh, so credits may be
wrong) with the final cleanup removed:

1. remove the extra put from svc_delete_xprt().
2,3. Revert 2 problematic patches which caused the oops people
are seeing.
4. Fix the original bug from the rdma series.

And the first 3 will go to stable as well. The 4th might eventually
too, it just seems less urgent.

I also agree with the cleanup that moves the svc_xprt_received to one
place, I'm just hoping you won't mind regenerating it against this.

--b.

>From ab1b18f70a007ea6caeb007d269abb75b131a410 Mon Sep 17 00:00:00 2001
From: Neil Brown <neilb@suse.de>
Date: Sat, 27 Feb 2010 09:33:40 +1100
Subject: [PATCH 1/4] sunrpc: remove unnecessary svc_xprt_put

The 'struct svc_deferred_req's on the xpt_deferred queue do not
own a reference to the owning xprt. This is seen in svc_revisit
which is where things are added to this queue. dr->xprt is set to
NULL and the reference to the xprt it put.

So when this list is cleaned up in svc_delete_xprt, we mustn't
put the reference.

Also, replace the 'for' with a 'while' which is arguably
simpler and more likely to compile efficiently.

Cc: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
---
net/sunrpc/svc_xprt.c | 5 +----
1 files changed, 1 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index d7ec5ca..0983830 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -896,11 +896,8 @@ void svc_delete_xprt(struct svc_xprt *xprt)
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);
+ while ((dr = svc_deferred_dequeue(xprt)) != NULL)
kfree(dr);
- }

svc_xprt_put(xprt);
spin_unlock_bh(&serv->sv_lock);
--
1.6.3.3

>From 56dd703462dad7311f3c5a736343f38d7b34b965 Mon Sep 17 00:00:00 2001
From: J. Bruce Fields <bfields@citi.umich.edu>
Date: Sun, 28 Feb 2010 16:32:51 -0500
Subject: [PATCH 2/4] Revert "sunrpc: fix peername failed on closed listener"

This reverts commit b292cf9ce70d221c3f04ff62db5ab13d9a249ca8. The
commit that it attempted to patch up, b0401d "sunrpc: fix peername
failed on closed listener" was fundamentally wrong, and will also be
reverted.

Cc: stable@kernel.org
Cc: Xiaotian Feng <dfeng@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
---
net/sunrpc/svc_xprt.c | 3 +--
1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 0983830..818c4c3 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -706,8 +706,7 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
spin_unlock_bh(&pool->sp_lock);

len = 0;
- if (test_bit(XPT_LISTENER, &xprt->xpt_flags) &&
- !test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
+ if (test_bit(XPT_LISTENER, &xprt->xpt_flags)) {
struct svc_xprt *newxpt;
newxpt = xprt->xpt_ops->xpo_accept(xprt);
if (newxpt) {
--
1.6.3.3

>From 4d87b1d6c9832b19068f662101d27c82f3bb659d Mon Sep 17 00:00:00 2001
From: J. Bruce Fields <bfields@citi.umich.edu>
Date: Sun, 28 Feb 2010 16:33:31 -0500
Subject: [PATCH 3/4] Revert "sunrpc: move the close processing after do recvfrom method"

This reverts commit b0401d725334a94d57335790b8ac2404144748ee, which
moved svc_delete_xprt() outside of XPT_BUSY, and allowed it to be called
after svc_xpt_recived(), removing the xprt's last reference and
destroying the xprt after it had already been queued for future
processing.

Cc: Wei Yongjun <yjwei@cn.fujitsu.com>
Cc: stable_kernel.org
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
---
net/sunrpc/svc_xprt.c | 12 +++++-------
1 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 818c4c3..8f0f1fb 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -706,7 +706,10 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
spin_unlock_bh(&pool->sp_lock);

len = 0;
- if (test_bit(XPT_LISTENER, &xprt->xpt_flags)) {
+ if (test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
+ dprintk("svc_recv: found XPT_CLOSE\n");
+ svc_delete_xprt(xprt);
+ } else if (test_bit(XPT_LISTENER, &xprt->xpt_flags)) {
struct svc_xprt *newxpt;
newxpt = xprt->xpt_ops->xpo_accept(xprt);
if (newxpt) {
@@ -732,7 +735,7 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
svc_xprt_received(newxpt);
}
svc_xprt_received(xprt);
- } else if (!test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
+ } else {
dprintk("svc: server %p, pool %u, transport %p, inuse=%d\n",
rqstp, pool->sp_id, xprt,
atomic_read(&xprt->xpt_ref.refcount));
@@ -745,11 +748,6 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
dprintk("svc: got len=%d\n", len);
}

- if (test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
- dprintk("svc_recv: found XPT_CLOSE\n");
- svc_delete_xprt(xprt);
- }
-
/* No data, incomplete (TCP) read, or accept() */
if (len == 0 || len == -EAGAIN) {
rqstp->rq_res.len = 0;
--
1.6.3.3

>From f41357becb29e874a7adf4d77d52c31cb7b91820 Mon Sep 17 00:00:00 2001
From: Neil Brown <neilb@suse.de>
Date: Sun, 28 Feb 2010 22:01:05 -0500
Subject: [PATCH 4/4] nfsd: ensure sockets are closed on error

One of the changes in commit d7979ae4a "svc: Move close processing to a
single place" is:

err_delete:
- svc_delete_socket(svsk);
+ set_bit(SK_CLOSE, &svsk->sk_flags);
return -EAGAIN;

This is insufficient. The recvfrom methods must always call
svc_xprt_received on completion so that the socket gets re-queued if
there is any more work to do. This particular path did not make that
call because it actually destroyed the svsk, making requeue pointless.
When the svc_delete_socket was change to just set a bit, we should have
added a call to svc_xprt_received,

This is the problem that b0401d7253 attempted to fix, incorrectly.

Cc: Tom Tucker <tom@opengridcomputing.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Greg Banks <gnb-xTcybq6BZ68@public.gmane.org>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
---
net/sunrpc/svcsock.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 9e09391..a29f259 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -968,6 +968,7 @@ static int svc_tcp_recv_record(struct svc_sock *svsk, struct svc_rqst *rqstp)
return len;
err_delete:
set_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags);
+ svc_xprt_received(&svsk->sk_xprt);
err_again:
return -EAGAIN;
}
--
1.6.3.3