From b4f36f88b3ee7cf26bf0be84e6c7fc15f84dcb71 Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Tue, 29 Nov 2011 17:00:26 -0500 Subject: [PATCH] svcrpc: avoid memory-corruption on pool shutdown 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 Cc: Jeff Layton Cc: stable@kernel.org Signed-off-by: J. Bruce Fields --- net/sunrpc/svc.c | 10 ++++++++- net/sunrpc/svc_xprt.c | 48 ++++++++++++++++++++++++++----------------- 2 files changed, 38 insertions(+), 20 deletions(-) diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c index 60babf0a9847..1a6c16ed7fa6 100644 --- a/net/sunrpc/svc.c +++ b/net/sunrpc/svc.c @@ -527,7 +527,15 @@ svc_destroy(struct svc_serv *serv) printk("svc_destroy: no threads for serv=%p!\n", serv); del_timer_sync(&serv->sv_temptimer); - + /* + * The set of xprts (contained in the sv_tempsocks and + * sv_permsocks lists) is now constant, since it is modified + * only by accepting new sockets (done by service threads in + * svc_recv) or aging old ones (done by sv_temptimer), or + * configuration changes (excluded by whatever locking the + * caller is using--nfsd_mutex in the case of nfsd). So it's + * safe to traverse those lists and shut everything down: + */ svc_close_all(serv); if (serv->sv_shutdown) diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index 099ddf99d2a1..0d80c064e634 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)); - } /*