[PATCH] [23/50] svcrpc: fix list-corrupting race on nfsd shutdown

Andi Kleen
2011-07-28T23:52:23Z

From: J. Bruce Fields <bfields@redhat.com>

[ upstream commit ebc63e531cc6a457595dd110b07ac530eae788c3 ]

After commit 3262c816a3d7fb1eaabce633caa317887ed549ae "[PATCH] knfsd:
split svc_serv into pools", svc_delete_xprt (then svc_delete_socket) no
longer removed its xpt_ready (then sk_ready) field from whatever list it
was on, noting that there was no point since the whole list was about to
be destroyed anyway.

That was mostly true, but forgot that a few svc_xprt_enqueue()'s might
still be hanging around playing with the about-to-be-destroyed list, and
could get themselves into trouble writing to freed memory if we left
this xprt on the list after freeing it.

(This is actually functionally identical to a patch made first by Ben
Greear, but with more comments.)

Cc: stable@kernel.org
Cc: gnb@fmeh.org
Reported-by: Ben Greear <greearb@candelatech.com>
Tested-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

Index: linux-2.6.35.y/net/sunrpc/svc_xprt.c
===================================================================
--- linux-2.6.35.y.orig/net/sunrpc/svc_xprt.c
+++ linux-2.6.35.y/net/sunrpc/svc_xprt.c
@@ -894,12 +894,13 @@ void svc_delete_xprt(struct svc_xprt *xp
if (!test_and_set_bit(XPT_DETACHED, &xprt->xpt_flags))
list_del_init(&xprt->xpt_list);
/*
- * We used to delete the transport from whichever list
- * it's sk_xprt.xpt_ready node was on, but we don't actually
- * need to. This is because the only time we're called
- * while still attached to a queue, the queue itself
- * is about to be destroyed (in svc_destroy).
+ * The only time we're called while xpt_ready is still on a list
+ * is while the list itself is about to be destroyed (in
+ * svc_destroy). BUT svc_xprt_enqueue could still be attempting
+ * to add new entries to the sp_sockets list, so we can't leave
+ * a freed xprt on it.
*/
+ list_del_init(&xprt->xpt_ready);
if (test_bit(XPT_TEMP, &xprt->xpt_flags))
serv->sv_tmpcnt--;
spin_unlock_bh(&serv->sv_lock);