Re: [PATCH_V3 1/7] NFS dont free shared socket on backchannel put xprt

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On Dec 14, 2010, at 5:36 PM, J. Bruce Fields wrote:

On Tue, Dec 14, 2010 at 05:28:51PM -0500, Andy Adamson wrote:

On Dec 14, 2010, at 4:56 PM, J. Bruce Fields wrote:

On Tue, Dec 14, 2010 at 04:44:58PM -0500, Andy Adamson wrote:

On Dec 14, 2010, at 1:19 PM, J. Bruce Fields wrote:

On Mon, Dec 13, 2010 at 03:19:39PM -0500, Andy Adamson wrote:
Fixes this bug:
fedora-64 kernel: Invoking bc_svc_procass()
fedora-64 kernel: nfs_callback_authenticate SVC_DROP
fedora-64 kernel: BUG: unable to handle kernel NULL pointer
dereference at 0000000000000018 IP: [<ffffffffa0156140>]
svc_sock_free+0x32/0x56 [sunrpc]

Signed-off-by: Andy Adamson <andros@xxxxxxxxxx>
---
fs/nfs/callback.c               |    3 +++
include/linux/sunrpc/svc_xprt.h |    1 +
net/sunrpc/svc_xprt.c           |    3 ++-
3 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 93a8b3b..023a9eb 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -193,6 +193,9 @@ nfs41_callback_up(struct svc_serv *serv,
struct rpc_xprt *xprt)
	serv->bc_xprt = bc_xprt;
	xprt->bc_serv = serv;

+	/* socket is shared with the fore channel */
+	set_bit(XPT_SHARE_SOCK, &bc_xprt->xpt_flags);
+
	INIT_LIST_HEAD(&serv->sv_cb_list);
	spin_lock_init(&serv->sv_cb_lock);
	init_waitqueue_head(&serv->sv_cb_waitq);
diff --git a/include/linux/sunrpc/svc_xprt.h
b/include/linux/sunrpc/svc_xprt.h
index aea0d43..600c669 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -62,6 +62,7 @@ struct svc_xprt {
#define	XPT_DETACHED	10		/* detached from tempsocks list */
#define XPT_LISTENER	11		/* listening endpoint */
#define XPT_CACHE_AUTH	12		/* cache auth info */
+#define XPT_SHARE_SOCK	13		/* fore and back channel share
socket */

	struct svc_pool		*xpt_pool;	/* current pool iff queued */
	struct svc_serv		*xpt_server;	/* service for transport */
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index ea2ff78..8c4d9ad 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -128,7 +128,8 @@ static void svc_xprt_free(struct kref *kref)
	if (test_bit(XPT_CACHE_AUTH, &xprt->xpt_flags))
		svcauth_unix_info_release(xprt);
	put_net(xprt->xpt_net);
-	xprt->xpt_ops->xpo_free(xprt);
+	if (!test_bit(XPT_SHARE_SOCK, &xprt->xpt_flags))
+		xprt->xpt_ops->xpo_free(xprt);

So when does the svc_xprt get freed if not here?

svc_sock_destroy frees the bc_xprt, called by svc_destroy on the
serv->bc_xprt.

Can you remove the

	#if defined(CONFIG_NFS_V4_1)
     	svc_sock_destroy(serv->bc_xprt);
	#endif /* CONFIG_NFS_V4_1 */

from svc_destroy instead?

Instead of what?

Instead of the patch above.

Sorry, I just don't understand how that will solve the sock_free BUG above.

-->Andy

--b.

Where do you want svc_sock_destroy to be called?

From svc_xprt_free?


And why is it OK to do
the put_net() and module_put() but not the xpo_free()?

svc_sock_create()  called only by nfs41_callback_up creates the
bc_xprt. It calls svc_xprt_init which calls get_net(), so put_net is
needed.

Hmmm. It looks like the module_put is also not needed - the matching
module_get is in svc_create_xprt() which is not called for the
NFSv4.1 callback service. (but is called for the NFSv4.0 callback
service ... sheese).

I'll move the module_put so it is also not called when the
XPT_SHARE_SOCK flag is set.

The xpt_net reference counting doesn't look right either.

I'm not familiar with the xpt_net reference counting.


I think we shouldn't need XPT_SHARE_SOCK if we just get the
reference counting
on the svc_xprt right instead.

At the end of the day svc_xprt_free will be called on this svc_xprt.
At that time, xpo_free can not be called because xpo_create was not
used to create it. svc_sock_destroy needs to be called to free the
storage kzalloc'ed in svc_sock_create.

I don't get what you are suggesting.....




Something feels wrong here....

Yeah - how about naming the server back channel xprt (bc_xprt) the
same as the client back channel xprt (bc_xprt)!!! How confusing is
THAT! :)

Well, and it's also the name of a field in svc_serv.  If nothing
else, would
you mind renaming that to sv_bc_xprt?

I can clean up the naming after we figure out the above.

-->Andy


--b.


Thanks for the review.

-->Andy


--b.

	module_put(owner);
}

--
1.6.6

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