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 ebc63e531c
"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>
Cc: stable@kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
parent
2fefb8a09e
commit
b4f36f88b3
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@ -527,7 +527,15 @@ svc_destroy(struct svc_serv *serv)
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printk("svc_destroy: no threads for serv=%p!\n", serv);
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del_timer_sync(&serv->sv_temptimer);
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/*
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* The set of xprts (contained in the sv_tempsocks and
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* sv_permsocks lists) is now constant, since it is modified
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* only by accepting new sockets (done by service threads in
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* svc_recv) or aging old ones (done by sv_temptimer), or
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* configuration changes (excluded by whatever locking the
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* caller is using--nfsd_mutex in the case of nfsd). So it's
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* safe to traverse those lists and shut everything down:
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*/
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svc_close_all(serv);
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if (serv->sv_shutdown)
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@ -894,14 +894,7 @@ static void svc_delete_xprt(struct svc_xprt *xprt)
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spin_lock_bh(&serv->sv_lock);
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if (!test_and_set_bit(XPT_DETACHED, &xprt->xpt_flags))
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list_del_init(&xprt->xpt_list);
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/*
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* The only time we're called while xpt_ready is still on a list
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* is while the list itself is about to be destroyed (in
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* svc_destroy). BUT svc_xprt_enqueue could still be attempting
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* to add new entries to the sp_sockets list, so we can't leave
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* a freed xprt on it.
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*/
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list_del_init(&xprt->xpt_ready);
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BUG_ON(!list_empty(&xprt->xpt_ready));
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if (test_bit(XPT_TEMP, &xprt->xpt_flags))
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serv->sv_tmpcnt--;
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spin_unlock_bh(&serv->sv_lock);
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@ -932,28 +925,45 @@ EXPORT_SYMBOL_GPL(svc_close_xprt);
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static void svc_close_list(struct list_head *xprt_list)
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{
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struct svc_xprt *xprt;
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struct svc_xprt *tmp;
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/*
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* The server is shutting down, and no more threads are running.
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* svc_xprt_enqueue() might still be running, but at worst it
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* will re-add the xprt to sp_sockets, which will soon get
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* freed. So we don't bother with any more locking, and don't
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* leave the close to the (nonexistent) server threads:
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*/
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list_for_each_entry_safe(xprt, tmp, xprt_list, xpt_list) {
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list_for_each_entry(xprt, xprt_list, xpt_list) {
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set_bit(XPT_CLOSE, &xprt->xpt_flags);
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svc_delete_xprt(xprt);
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set_bit(XPT_BUSY, &xprt->xpt_flags);
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}
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}
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void svc_close_all(struct svc_serv *serv)
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{
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struct svc_pool *pool;
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struct svc_xprt *xprt;
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struct svc_xprt *tmp;
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int i;
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svc_close_list(&serv->sv_tempsocks);
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svc_close_list(&serv->sv_permsocks);
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for (i = 0; i < serv->sv_nrpools; i++) {
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pool = &serv->sv_pools[i];
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spin_lock_bh(&pool->sp_lock);
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while (!list_empty(&pool->sp_sockets)) {
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xprt = list_first_entry(&pool->sp_sockets, struct svc_xprt, xpt_ready);
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list_del_init(&xprt->xpt_ready);
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}
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spin_unlock_bh(&pool->sp_lock);
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}
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/*
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* At this point the sp_sockets lists will stay empty, since
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* svc_enqueue will not add new entries without taking the
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* sp_lock and checking XPT_BUSY.
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*/
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list_for_each_entry_safe(xprt, tmp, &serv->sv_tempsocks, xpt_list)
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svc_delete_xprt(xprt);
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list_for_each_entry_safe(xprt, tmp, &serv->sv_permsocks, xpt_list)
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svc_delete_xprt(xprt);
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BUG_ON(!list_empty(&serv->sv_permsocks));
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BUG_ON(!list_empty(&serv->sv_tempsocks));
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}
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/*
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