[PATCH 35/91] svcrpc: fix list-corrupting race on nfsd shutdown

From: Willy Tarreau
Date: Sun Feb 05 2012 - 17:41:31 EST

2.6.27-longterm review patch. If anyone has any objections, please let us know.


commit ebc63e531cc6a457595dd110b07ac530eae788c3 upstream.

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: gnb@xxxxxxxx
Reported-by: Ben Greear <greearb@xxxxxxxxxxxxxxx>
Tested-by: Ben Greear <greearb@xxxxxxxxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
net/sunrpc/svc_xprt.c | 11 ++++++-----
1 files changed, 6 insertions(+), 5 deletions(-)

Index: longterm-2.6.27/net/sunrpc/svc_xprt.c
--- longterm-2.6.27.orig/net/sunrpc/svc_xprt.c 2012-02-05 22:34:33.947915241 +0100
+++ longterm-2.6.27/net/sunrpc/svc_xprt.c 2012-02-05 22:34:39.823917910 +0100
@@ -830,12 +830,13 @@
if (!test_and_set_bit(XPT_DETACHED, &xprt->xpt_flags))
- * 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))

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