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bdc54d8e3c
If there were less than 2 entries in the multipath list, then
xprt_iter_next_entry_multiple() would never advance beyond the
first entry, which is correct for round robin behaviour, but not
for the list iteration.
The end result would be infinite looping in rpc_clnt_iterate_for_each_xprt()
as we would never see the xprt == NULL condition fulfilled.
Reported-by: Oleg Drokin <green@linuxhacker.ru>
Fixes: 80b14d5e61 ("SUNRPC: Add a structure to track multiple transports")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
474 lines
12 KiB
C
474 lines
12 KiB
C
/*
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* Multipath support for RPC
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*
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* Copyright (c) 2015, 2016, Primary Data, Inc. All rights reserved.
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*
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* Trond Myklebust <trond.myklebust@primarydata.com>
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*
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*/
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#include <linux/types.h>
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#include <linux/kref.h>
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#include <linux/list.h>
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#include <linux/rcupdate.h>
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#include <linux/rculist.h>
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#include <linux/slab.h>
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#include <asm/cmpxchg.h>
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#include <linux/spinlock.h>
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#include <linux/sunrpc/xprt.h>
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#include <linux/sunrpc/xprtmultipath.h>
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typedef struct rpc_xprt *(*xprt_switch_find_xprt_t)(struct list_head *head,
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const struct rpc_xprt *cur);
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static const struct rpc_xprt_iter_ops rpc_xprt_iter_singular;
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static const struct rpc_xprt_iter_ops rpc_xprt_iter_roundrobin;
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static const struct rpc_xprt_iter_ops rpc_xprt_iter_listall;
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static void xprt_switch_add_xprt_locked(struct rpc_xprt_switch *xps,
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struct rpc_xprt *xprt)
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{
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if (unlikely(xprt_get(xprt) == NULL))
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return;
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list_add_tail_rcu(&xprt->xprt_switch, &xps->xps_xprt_list);
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smp_wmb();
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if (xps->xps_nxprts == 0)
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xps->xps_net = xprt->xprt_net;
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xps->xps_nxprts++;
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}
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/**
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* rpc_xprt_switch_add_xprt - Add a new rpc_xprt to an rpc_xprt_switch
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* @xps: pointer to struct rpc_xprt_switch
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* @xprt: pointer to struct rpc_xprt
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*
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* Adds xprt to the end of the list of struct rpc_xprt in xps.
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*/
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void rpc_xprt_switch_add_xprt(struct rpc_xprt_switch *xps,
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struct rpc_xprt *xprt)
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{
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if (xprt == NULL)
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return;
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spin_lock(&xps->xps_lock);
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if (xps->xps_net == xprt->xprt_net || xps->xps_net == NULL)
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xprt_switch_add_xprt_locked(xps, xprt);
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spin_unlock(&xps->xps_lock);
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}
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static void xprt_switch_remove_xprt_locked(struct rpc_xprt_switch *xps,
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struct rpc_xprt *xprt)
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{
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if (unlikely(xprt == NULL))
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return;
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xps->xps_nxprts--;
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if (xps->xps_nxprts == 0)
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xps->xps_net = NULL;
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smp_wmb();
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list_del_rcu(&xprt->xprt_switch);
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}
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/**
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* rpc_xprt_switch_remove_xprt - Removes an rpc_xprt from a rpc_xprt_switch
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* @xps: pointer to struct rpc_xprt_switch
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* @xprt: pointer to struct rpc_xprt
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*
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* Removes xprt from the list of struct rpc_xprt in xps.
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*/
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void rpc_xprt_switch_remove_xprt(struct rpc_xprt_switch *xps,
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struct rpc_xprt *xprt)
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{
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spin_lock(&xps->xps_lock);
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xprt_switch_remove_xprt_locked(xps, xprt);
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spin_unlock(&xps->xps_lock);
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xprt_put(xprt);
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}
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/**
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* xprt_switch_alloc - Allocate a new struct rpc_xprt_switch
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* @xprt: pointer to struct rpc_xprt
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* @gfp_flags: allocation flags
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*
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* On success, returns an initialised struct rpc_xprt_switch, containing
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* the entry xprt. Returns NULL on failure.
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*/
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struct rpc_xprt_switch *xprt_switch_alloc(struct rpc_xprt *xprt,
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gfp_t gfp_flags)
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{
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struct rpc_xprt_switch *xps;
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xps = kmalloc(sizeof(*xps), gfp_flags);
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if (xps != NULL) {
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spin_lock_init(&xps->xps_lock);
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kref_init(&xps->xps_kref);
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xps->xps_nxprts = 0;
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INIT_LIST_HEAD(&xps->xps_xprt_list);
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xps->xps_iter_ops = &rpc_xprt_iter_singular;
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xprt_switch_add_xprt_locked(xps, xprt);
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}
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return xps;
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}
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static void xprt_switch_free_entries(struct rpc_xprt_switch *xps)
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{
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spin_lock(&xps->xps_lock);
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while (!list_empty(&xps->xps_xprt_list)) {
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struct rpc_xprt *xprt;
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xprt = list_first_entry(&xps->xps_xprt_list,
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struct rpc_xprt, xprt_switch);
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xprt_switch_remove_xprt_locked(xps, xprt);
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spin_unlock(&xps->xps_lock);
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xprt_put(xprt);
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spin_lock(&xps->xps_lock);
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}
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spin_unlock(&xps->xps_lock);
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}
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static void xprt_switch_free(struct kref *kref)
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{
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struct rpc_xprt_switch *xps = container_of(kref,
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struct rpc_xprt_switch, xps_kref);
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xprt_switch_free_entries(xps);
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kfree_rcu(xps, xps_rcu);
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}
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/**
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* xprt_switch_get - Return a reference to a rpc_xprt_switch
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* @xps: pointer to struct rpc_xprt_switch
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*
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* Returns a reference to xps unless the refcount is already zero.
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*/
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struct rpc_xprt_switch *xprt_switch_get(struct rpc_xprt_switch *xps)
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{
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if (xps != NULL && kref_get_unless_zero(&xps->xps_kref))
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return xps;
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return NULL;
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}
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/**
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* xprt_switch_put - Release a reference to a rpc_xprt_switch
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* @xps: pointer to struct rpc_xprt_switch
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*
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* Release the reference to xps, and free it once the refcount is zero.
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*/
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void xprt_switch_put(struct rpc_xprt_switch *xps)
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{
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if (xps != NULL)
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kref_put(&xps->xps_kref, xprt_switch_free);
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}
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/**
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* rpc_xprt_switch_set_roundrobin - Set a round-robin policy on rpc_xprt_switch
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* @xps: pointer to struct rpc_xprt_switch
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*
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* Sets a round-robin default policy for iterators acting on xps.
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*/
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void rpc_xprt_switch_set_roundrobin(struct rpc_xprt_switch *xps)
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{
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if (READ_ONCE(xps->xps_iter_ops) != &rpc_xprt_iter_roundrobin)
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WRITE_ONCE(xps->xps_iter_ops, &rpc_xprt_iter_roundrobin);
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}
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static
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const struct rpc_xprt_iter_ops *xprt_iter_ops(const struct rpc_xprt_iter *xpi)
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{
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if (xpi->xpi_ops != NULL)
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return xpi->xpi_ops;
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return rcu_dereference(xpi->xpi_xpswitch)->xps_iter_ops;
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}
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static
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void xprt_iter_no_rewind(struct rpc_xprt_iter *xpi)
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{
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}
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static
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void xprt_iter_default_rewind(struct rpc_xprt_iter *xpi)
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{
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WRITE_ONCE(xpi->xpi_cursor, NULL);
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}
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static
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struct rpc_xprt *xprt_switch_find_first_entry(struct list_head *head)
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{
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return list_first_or_null_rcu(head, struct rpc_xprt, xprt_switch);
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}
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static
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struct rpc_xprt *xprt_iter_first_entry(struct rpc_xprt_iter *xpi)
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{
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struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
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if (xps == NULL)
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return NULL;
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return xprt_switch_find_first_entry(&xps->xps_xprt_list);
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}
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static
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struct rpc_xprt *xprt_switch_find_current_entry(struct list_head *head,
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const struct rpc_xprt *cur)
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{
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struct rpc_xprt *pos;
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list_for_each_entry_rcu(pos, head, xprt_switch) {
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if (cur == pos)
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return pos;
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}
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return NULL;
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}
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static
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struct rpc_xprt *xprt_iter_current_entry(struct rpc_xprt_iter *xpi)
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{
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struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
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struct list_head *head;
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if (xps == NULL)
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return NULL;
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head = &xps->xps_xprt_list;
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if (xpi->xpi_cursor == NULL || xps->xps_nxprts < 2)
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return xprt_switch_find_first_entry(head);
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return xprt_switch_find_current_entry(head, xpi->xpi_cursor);
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}
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static
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struct rpc_xprt *xprt_switch_find_next_entry(struct list_head *head,
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const struct rpc_xprt *cur)
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{
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struct rpc_xprt *pos, *prev = NULL;
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list_for_each_entry_rcu(pos, head, xprt_switch) {
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if (cur == prev)
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return pos;
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prev = pos;
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}
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return NULL;
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}
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static
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struct rpc_xprt *xprt_switch_set_next_cursor(struct list_head *head,
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struct rpc_xprt **cursor,
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xprt_switch_find_xprt_t find_next)
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{
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struct rpc_xprt *cur, *pos, *old;
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cur = READ_ONCE(*cursor);
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for (;;) {
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old = cur;
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pos = find_next(head, old);
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if (pos == NULL)
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break;
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cur = cmpxchg_relaxed(cursor, old, pos);
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if (cur == old)
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break;
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}
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return pos;
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}
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static
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struct rpc_xprt *xprt_iter_next_entry_multiple(struct rpc_xprt_iter *xpi,
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xprt_switch_find_xprt_t find_next)
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{
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struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
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if (xps == NULL)
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return NULL;
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return xprt_switch_set_next_cursor(&xps->xps_xprt_list,
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&xpi->xpi_cursor,
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find_next);
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}
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static
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struct rpc_xprt *xprt_switch_find_next_entry_roundrobin(struct list_head *head,
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const struct rpc_xprt *cur)
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{
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struct rpc_xprt *ret;
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ret = xprt_switch_find_next_entry(head, cur);
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if (ret != NULL)
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return ret;
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return xprt_switch_find_first_entry(head);
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}
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static
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struct rpc_xprt *xprt_iter_next_entry_roundrobin(struct rpc_xprt_iter *xpi)
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{
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return xprt_iter_next_entry_multiple(xpi,
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xprt_switch_find_next_entry_roundrobin);
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}
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static
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struct rpc_xprt *xprt_iter_next_entry_all(struct rpc_xprt_iter *xpi)
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{
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return xprt_iter_next_entry_multiple(xpi, xprt_switch_find_next_entry);
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}
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/*
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* xprt_iter_rewind - Resets the xprt iterator
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* @xpi: pointer to rpc_xprt_iter
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*
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* Resets xpi to ensure that it points to the first entry in the list
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* of transports.
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*/
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static
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void xprt_iter_rewind(struct rpc_xprt_iter *xpi)
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{
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rcu_read_lock();
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xprt_iter_ops(xpi)->xpi_rewind(xpi);
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rcu_read_unlock();
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}
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static void __xprt_iter_init(struct rpc_xprt_iter *xpi,
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struct rpc_xprt_switch *xps,
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const struct rpc_xprt_iter_ops *ops)
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{
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rcu_assign_pointer(xpi->xpi_xpswitch, xprt_switch_get(xps));
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xpi->xpi_cursor = NULL;
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xpi->xpi_ops = ops;
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}
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/**
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* xprt_iter_init - Initialise an xprt iterator
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* @xpi: pointer to rpc_xprt_iter
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* @xps: pointer to rpc_xprt_switch
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*
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* Initialises the iterator to use the default iterator ops
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* as set in xps. This function is mainly intended for internal
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* use in the rpc_client.
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*/
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void xprt_iter_init(struct rpc_xprt_iter *xpi,
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struct rpc_xprt_switch *xps)
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{
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__xprt_iter_init(xpi, xps, NULL);
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}
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/**
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* xprt_iter_init_listall - Initialise an xprt iterator
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* @xpi: pointer to rpc_xprt_iter
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* @xps: pointer to rpc_xprt_switch
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*
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* Initialises the iterator to iterate once through the entire list
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* of entries in xps.
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*/
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void xprt_iter_init_listall(struct rpc_xprt_iter *xpi,
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struct rpc_xprt_switch *xps)
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{
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__xprt_iter_init(xpi, xps, &rpc_xprt_iter_listall);
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}
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/**
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* xprt_iter_xchg_switch - Atomically swap out the rpc_xprt_switch
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* @xpi: pointer to rpc_xprt_iter
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* @xps: pointer to a new rpc_xprt_switch or NULL
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*
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* Swaps out the existing xpi->xpi_xpswitch with a new value.
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*/
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struct rpc_xprt_switch *xprt_iter_xchg_switch(struct rpc_xprt_iter *xpi,
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struct rpc_xprt_switch *newswitch)
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{
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struct rpc_xprt_switch __rcu *oldswitch;
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/* Atomically swap out the old xpswitch */
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oldswitch = xchg(&xpi->xpi_xpswitch, RCU_INITIALIZER(newswitch));
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if (newswitch != NULL)
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xprt_iter_rewind(xpi);
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return rcu_dereference_protected(oldswitch, true);
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}
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/**
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* xprt_iter_destroy - Destroys the xprt iterator
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* @xpi pointer to rpc_xprt_iter
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*/
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void xprt_iter_destroy(struct rpc_xprt_iter *xpi)
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{
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xprt_switch_put(xprt_iter_xchg_switch(xpi, NULL));
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}
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/**
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* xprt_iter_xprt - Returns the rpc_xprt pointed to by the cursor
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* @xpi: pointer to rpc_xprt_iter
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*
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* Returns a pointer to the struct rpc_xprt that is currently
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* pointed to by the cursor.
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* Caller must be holding rcu_read_lock().
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*/
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struct rpc_xprt *xprt_iter_xprt(struct rpc_xprt_iter *xpi)
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{
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WARN_ON_ONCE(!rcu_read_lock_held());
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return xprt_iter_ops(xpi)->xpi_xprt(xpi);
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}
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static
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struct rpc_xprt *xprt_iter_get_helper(struct rpc_xprt_iter *xpi,
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struct rpc_xprt *(*fn)(struct rpc_xprt_iter *))
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{
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struct rpc_xprt *ret;
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do {
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ret = fn(xpi);
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if (ret == NULL)
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break;
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ret = xprt_get(ret);
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} while (ret == NULL);
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return ret;
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}
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/**
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* xprt_iter_get_xprt - Returns the rpc_xprt pointed to by the cursor
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* @xpi: pointer to rpc_xprt_iter
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*
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* Returns a reference to the struct rpc_xprt that is currently
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* pointed to by the cursor.
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*/
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struct rpc_xprt *xprt_iter_get_xprt(struct rpc_xprt_iter *xpi)
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{
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struct rpc_xprt *xprt;
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rcu_read_lock();
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xprt = xprt_iter_get_helper(xpi, xprt_iter_ops(xpi)->xpi_xprt);
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rcu_read_unlock();
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return xprt;
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}
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/**
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* xprt_iter_get_next - Returns the next rpc_xprt following the cursor
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* @xpi: pointer to rpc_xprt_iter
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*
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* Returns a reference to the struct rpc_xprt that immediately follows the
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* entry pointed to by the cursor.
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*/
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struct rpc_xprt *xprt_iter_get_next(struct rpc_xprt_iter *xpi)
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{
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struct rpc_xprt *xprt;
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rcu_read_lock();
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xprt = xprt_iter_get_helper(xpi, xprt_iter_ops(xpi)->xpi_next);
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rcu_read_unlock();
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return xprt;
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}
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/* Policy for always returning the first entry in the rpc_xprt_switch */
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static
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const struct rpc_xprt_iter_ops rpc_xprt_iter_singular = {
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.xpi_rewind = xprt_iter_no_rewind,
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.xpi_xprt = xprt_iter_first_entry,
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.xpi_next = xprt_iter_first_entry,
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};
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/* Policy for round-robin iteration of entries in the rpc_xprt_switch */
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static
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const struct rpc_xprt_iter_ops rpc_xprt_iter_roundrobin = {
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.xpi_rewind = xprt_iter_default_rewind,
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.xpi_xprt = xprt_iter_current_entry,
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.xpi_next = xprt_iter_next_entry_roundrobin,
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};
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/* Policy for once-through iteration of entries in the rpc_xprt_switch */
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static
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const struct rpc_xprt_iter_ops rpc_xprt_iter_listall = {
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.xpi_rewind = xprt_iter_default_rewind,
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.xpi_xprt = xprt_iter_current_entry,
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.xpi_next = xprt_iter_next_entry_all,
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};
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