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svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet 

RDMA_READ completions are kept on a separate queue from the general
I/O request queue. Since a separate lock is used to protect the RDMA_READ
completion queue, a race exists between the dto_tasklet and the
svc_rdma_recvfrom thread where the dto_tasklet sets the XPT_DATA
bit and adds I/O to the read-completion queue. Concurrently, the
recvfrom thread checks the generic queue, finds it empty and resets
the XPT_DATA bit. A subsequent svc_xprt_enqueue will fail to enqueue
the transport for I/O and cause the transport to "stall".

The fix is to protect both lists with the same lock and set the XPT_DATA
bit with this lock held.

Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
This commit is contained in:
Tom Tucker 2008-08-13 11:05:41 -05:00 committed by J. Bruce Fields
parent 30a2f3c60a
commit 24b8b44780
3 changed files with 6 additions and 8 deletions
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1
include/linux/sunrpc/svc_rdma.h
View File

@ -143,7 +143,6 @@ struct svcxprt_rdma {
unsigned long sc_flags;
struct list_head sc_dto_q; /* DTO tasklet I/O pending Q */
struct list_head sc_read_complete_q;
spinlock_t sc_read_complete_lock;
struct work_struct sc_work;
};
/* sc_flags */

8
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
View File

@ -443,18 +443,18 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
dprintk("svcrdma: rqstp=%p\n", rqstp);
spin_lock_bh(&rdma_xprt->sc_read_complete_lock);
spin_lock_bh(&rdma_xprt->sc_rq_dto_lock);
if (!list_empty(&rdma_xprt->sc_read_complete_q)) {
ctxt = list_entry(rdma_xprt->sc_read_complete_q.next,
struct svc_rdma_op_ctxt,
dto_q);
list_del_init(&ctxt->dto_q);
}
spin_unlock_bh(&rdma_xprt->sc_read_complete_lock);
if (ctxt)
if (ctxt) {
spin_unlock_bh(&rdma_xprt->sc_rq_dto_lock);
return rdma_read_complete(rqstp, ctxt);
}
spin_lock_bh(&rdma_xprt->sc_rq_dto_lock);
if (!list_empty(&rdma_xprt->sc_rq_dto_q)) {
ctxt = list_entry(rdma_xprt->sc_rq_dto_q.next,
struct svc_rdma_op_ctxt,

5
net/sunrpc/xprtrdma/svc_rdma_transport.c
View File

@ -359,11 +359,11 @@ static void sq_cq_reap(struct svcxprt_rdma *xprt)
if (test_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags)) {
struct svc_rdma_op_ctxt *read_hdr = ctxt->read_hdr;
BUG_ON(!read_hdr);
spin_lock_bh(&xprt->sc_rq_dto_lock);
set_bit(XPT_DATA, &xprt->sc_xprt.xpt_flags);
spin_lock_bh(&xprt->sc_read_complete_lock);
list_add_tail(&read_hdr->dto_q,
&xprt->sc_read_complete_q);
spin_unlock_bh(&xprt->sc_read_complete_lock);
spin_unlock_bh(&xprt->sc_rq_dto_lock);
svc_xprt_enqueue(&xprt->sc_xprt);
}
svc_rdma_put_context(ctxt, 0);
@ -428,7 +428,6 @@ static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
init_waitqueue_head(&cma_xprt->sc_send_wait);
spin_lock_init(&cma_xprt->sc_lock);
spin_lock_init(&cma_xprt->sc_read_complete_lock);
spin_lock_init(&cma_xprt->sc_rq_dto_lock);
cma_xprt->sc_ord = svcrdma_ord;