From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
Socket callbacks use svc_xprt_enqueue() to add an xprt to a
pool->sp_sockets list. In normal operation a server thread will later
come along and take the xprt off that list. On shutdown, after all the
threads have exited, we instead manually walk the sv_tempsocks and
sv_permsocks lists to find all the xprt's and delete them.
So the sp_sockets lists don't really matter any more. As a result,
we've mostly just ignored them and hoped they would go away.
Which has gotten us into trouble; witness for example ebc63e531cc6
"svcrpc: fix list-corrupting race on nfsd shutdown", the result of Ben
Greear noticing that a still-running svc_xprt_enqueue() could re-add an
xprt to an sp_sockets list just before it was deleted. The fix was to
remove it from the list at the end of svc_delete_xprt(). But that only
made corruption less likely--I can see nothing that prevents a
svc_xprt_enqueue() from adding another xprt to the list at the same
moment that we're removing this xprt from the list. In fact, despite
the earlier xpo_detach(), I don't even see what guarantees that
svc_xprt_enqueue() couldn't still be running on this xprt.
So, instead, note that svc_xprt_enqueue() essentially does:
lock sp_lock
if XPT_BUSY unset
add to sp_sockets
unlock sp_lock
So, if we do:
set XPT_BUSY on every xprt.
Empty every sp_sockets list, under the sp_socks locks.
Then we're left knowing that the sp_sockets lists are all empty and will
stay that way, since any svc_xprt_enqueue() will check XPT_BUSY under
the sp_lock and see it set.
And *then* we can continue deleting the xprt's.
(Thanks to Jeff Layton for being correctly suspicious of this code....)
Cc: Ben Greear <greearb@xxxxxxxxxxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
---
net/sunrpc/svc_xprt.c | 48 +++++++++++++++++++++++++++++-------------------
1 files changed, 29 insertions(+), 19 deletions(-)
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 099ddf9..0d80c06 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -894,14 +894,7 @@ static void svc_delete_xprt(struct svc_xprt *xprt)
spin_lock_bh(&serv->sv_lock);
if (!test_and_set_bit(XPT_DETACHED, &xprt->xpt_flags))
list_del_init(&xprt->xpt_list);
- /*
- * 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);
+ BUG_ON(!list_empty(&xprt->xpt_ready));
if (test_bit(XPT_TEMP, &xprt->xpt_flags))
serv->sv_tmpcnt--;
spin_unlock_bh(&serv->sv_lock);
@@ -932,28 +925,45 @@ EXPORT_SYMBOL_GPL(svc_close_xprt);
static void svc_close_list(struct list_head *xprt_list)
{
struct svc_xprt *xprt;
- struct svc_xprt *tmp;
- /*
- * The server is shutting down, and no more threads are running.
- * svc_xprt_enqueue() might still be running, but at worst it
- * will re-add the xprt to sp_sockets, which will soon get
- * freed. So we don't bother with any more locking, and don't
- * leave the close to the (nonexistent) server threads:
- */
- list_for_each_entry_safe(xprt, tmp, xprt_list, xpt_list) {
+ list_for_each_entry(xprt, xprt_list, xpt_list) {
set_bit(XPT_CLOSE, &xprt->xpt_flags);
- svc_delete_xprt(xprt);
+ set_bit(XPT_BUSY, &xprt->xpt_flags);
}
}
void svc_close_all(struct svc_serv *serv)
{
+ struct svc_pool *pool;
+ struct svc_xprt *xprt;
+ struct svc_xprt *tmp;
+ int i;
+
svc_close_list(&serv->sv_tempsocks);
svc_close_list(&serv->sv_permsocks);
+
+ for (i = 0; i < serv->sv_nrpools; i++) {
+ pool = &serv->sv_pools[i];
+
+ spin_lock_bh(&pool->sp_lock);
+ while (!list_empty(&pool->sp_sockets)) {
+ xprt = list_first_entry(&pool->sp_sockets, struct svc_xprt, xpt_ready);
+ list_del_init(&xprt->xpt_ready);
+ }
+ spin_unlock_bh(&pool->sp_lock);
+ }
+ /*
+ * At this point the sp_sockets lists will stay empty, since
+ * svc_enqueue will not add new entries without taking the
+ * sp_lock and checking XPT_BUSY.
+ */
+ list_for_each_entry_safe(xprt, tmp, &serv->sv_tempsocks, xpt_list)
+ svc_delete_xprt(xprt);
+ list_for_each_entry_safe(xprt, tmp, &serv->sv_permsocks, xpt_list)
+ svc_delete_xprt(xprt);
+
BUG_ON(!list_empty(&serv->sv_permsocks));
BUG_ON(!list_empty(&serv->sv_tempsocks));
-
}
/*
--
1.7.5.4
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