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author | J. Bruce Fields <bfields@redhat.com> | 2011-11-29 17:00:26 -0500 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2012-01-25 17:24:48 -0800 |
commit | a141a5eb3ab45131cb168e7a561d662722b43ec3 (patch) | |
tree | f72da23ff947391cc5181842a34b39db81f1dc63 | |
parent | 7df22768c0af8769d805f6db21144d71d91fe13d (diff) | |
download | kernel_samsung_crespo-a141a5eb3ab45131cb168e7a561d662722b43ec3.zip kernel_samsung_crespo-a141a5eb3ab45131cb168e7a561d662722b43ec3.tar.gz kernel_samsung_crespo-a141a5eb3ab45131cb168e7a561d662722b43ec3.tar.bz2 |
svcrpc: avoid memory-corruption on pool shutdown
commit b4f36f88b3ee7cf26bf0be84e6c7fc15f84dcb71 upstream.
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@candelatech.com>
Cc: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r-- | net/sunrpc/svc.c | 10 | ||||
-rw-r--r-- | 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 4d5cb99..ce5f111 100644 --- a/net/sunrpc/svc.c +++ b/net/sunrpc/svc.c @@ -475,7 +475,15 @@ 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 9cb2621..9d7ed0b 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -901,14 +901,7 @@ 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); @@ -939,28 +932,45 @@ 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)); - } /* |