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SUNRPC: Fix a backchannel race 

We need to allow the server to send a new request immediately after we've
replied to the previous one. Right now, there is a window between the
send and the release of the old request in rpc_put_task(), where the
server could send us a new backchannel RPC call, and we have no
request to service it.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
This commit is contained in:
Trond Myklebust 2015-06-04 15:37:10 -04:00
parent 1dddda86c0
commit 0d2a970d0a
3 changed files with 31 additions and 15 deletions
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3
include/linux/sunrpc/xprt.h
View File

@ -212,7 +212,8 @@ struct rpc_xprt {
#if defined(CONFIG_SUNRPC_BACKCHANNEL)
struct svc_serv *bc_serv; /* The RPC service which will */
/* process the callback */
unsigned int bc_alloc_count; /* Total number of preallocs */
int bc_alloc_count; /* Total number of preallocs */
atomic_t bc_free_slots;
spinlock_t bc_pa_lock; /* Protects the preallocated
* items */
struct list_head bc_pa_list; /* List of preallocated

37
net/sunrpc/backchannel_rqst.c
View File

@ -37,16 +37,18 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
static inline int xprt_need_to_requeue(struct rpc_xprt *xprt)
{
return xprt->bc_alloc_count > 0;
return xprt->bc_alloc_count < atomic_read(&xprt->bc_free_slots);
}
static inline void xprt_inc_alloc_count(struct rpc_xprt *xprt, unsigned int n)
{
atomic_add(n, &xprt->bc_free_slots);
xprt->bc_alloc_count += n;
}
static inline int xprt_dec_alloc_count(struct rpc_xprt *xprt, unsigned int n)
{
atomic_sub(n, &xprt->bc_free_slots);
return xprt->bc_alloc_count -= n;
}
@ -232,9 +234,15 @@ static struct rpc_rqst *xprt_alloc_bc_request(struct rpc_xprt *xprt, __be32 xid)
struct rpc_rqst *req = NULL;
dprintk("RPC: allocate a backchannel request\n");
if (list_empty(&xprt->bc_pa_list))
if (atomic_read(&xprt->bc_free_slots) <= 0)
goto not_found;
if (list_empty(&xprt->bc_pa_list)) {
req = xprt_alloc_bc_req(xprt, GFP_ATOMIC);
if (!req)
goto not_found;
/* Note: this 'free' request adds it to xprt->bc_pa_list */
xprt_free_bc_request(req);
}
req = list_first_entry(&xprt->bc_pa_list, struct rpc_rqst,
rq_bc_pa_list);
req->rq_reply_bytes_recvd = 0;
@ -260,11 +268,21 @@ void xprt_free_bc_request(struct rpc_rqst *req)
req->rq_connect_cookie = xprt->connect_cookie - 1;
smp_mb__before_atomic();
WARN_ON_ONCE(!test_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state));
clear_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
smp_mb__after_atomic();
if (!xprt_need_to_requeue(xprt)) {
/*
* Return it to the list of preallocations so that it
* may be reused by a new callback request.
*/
spin_lock_bh(&xprt->bc_pa_lock);
if (xprt_need_to_requeue(xprt)) {
list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);
xprt->bc_alloc_count++;
req = NULL;
}
spin_unlock_bh(&xprt->bc_pa_lock);
if (req != NULL) {
/*
* The last remaining session was destroyed while this
* entry was in use. Free the entry and don't attempt
@ -275,14 +293,6 @@ void xprt_free_bc_request(struct rpc_rqst *req)
xprt_free_allocation(req);
return;
}
/*
* Return it to the list of preallocations so that it
* may be reused by a new callback request.
*/
spin_lock_bh(&xprt->bc_pa_lock);
list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);
spin_unlock_bh(&xprt->bc_pa_lock);
}
/*
@ -326,6 +336,7 @@ void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied)
spin_lock(&xprt->bc_pa_lock);
list_del(&req->rq_bc_pa_list);
xprt->bc_alloc_count--;
spin_unlock(&xprt->bc_pa_lock);
req->rq_private_buf.len = copied;

6
net/sunrpc/svc.c
View File

@ -1351,6 +1351,7 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
struct kvec *argv = &rqstp->rq_arg.head[0];
struct kvec *resv = &rqstp->rq_res.head[0];
struct rpc_task *task;
int proc_error;
int error;
dprintk("svc: %s(%p)\n", __func__, req);
@ -1382,7 +1383,10 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
svc_getnl(argv); /* CALLDIR */
/* Parse and execute the bc call */
if (!svc_process_common(rqstp, argv, resv)) {
proc_error = svc_process_common(rqstp, argv, resv);
atomic_inc(&req->rq_xprt->bc_free_slots);
if (!proc_error) {
/* Processing error: drop the request */
xprt_free_bc_request(req);
return 0;