2008-08-13 16:05:42

by Tom Tucker

[permalink] [raw]
Subject: [PATCH] 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 <[email protected]>

---
include/linux/sunrpc/svc_rdma.h | 1 -
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 8 ++++----
net/sunrpc/xprtrdma/svc_rdma_transport.c | 5 ++---
3 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index ef2e3a2..dc05b54 100644
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h
@@ -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 */
diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index b4b17f4..74de31a 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -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,
diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
index 19ddc38..900cb69 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
@@ -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;



2008-08-13 21:10:20

by [email protected]

[permalink] [raw]
Subject: Re: [PATCH] svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet

On Wed, Aug 13, 2008 at 11:05:41AM -0500, Tom Tucker wrote:
>
> 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 <[email protected]>

OK. As a bugfix, would you like this sent in now for 2.6.27?

--b.

>
> ---
> include/linux/sunrpc/svc_rdma.h | 1 -
> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 8 ++++----
> net/sunrpc/xprtrdma/svc_rdma_transport.c | 5 ++---
> 3 files changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
> index ef2e3a2..dc05b54 100644
> --- a/include/linux/sunrpc/svc_rdma.h
> +++ b/include/linux/sunrpc/svc_rdma.h
> @@ -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 */
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> index b4b17f4..74de31a 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> @@ -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,
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> index 19ddc38..900cb69 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> @@ -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;
>

2008-08-13 21:31:42

by Tom Tucker

[permalink] [raw]
Subject: Re: [PATCH] svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet

J. Bruce Fields wrote:
> On Wed, Aug 13, 2008 at 11:05:41AM -0500, Tom Tucker wrote:
>> 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 <[email protected]>
>
> OK. As a bugfix, would you like this sent in now for 2.6.27?
>

Yes I would if that's possible. I put it before all the other patches so it
would be independent.

Thanks,
Tom

> --b.
>
>> ---
>> include/linux/sunrpc/svc_rdma.h | 1 -
>> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 8 ++++----
>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 5 ++---
>> 3 files changed, 6 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
>> index ef2e3a2..dc05b54 100644
>> --- a/include/linux/sunrpc/svc_rdma.h
>> +++ b/include/linux/sunrpc/svc_rdma.h
>> @@ -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 */
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>> index b4b17f4..74de31a 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>> @@ -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,
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> index 19ddc38..900cb69 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> @@ -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;
>>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html


2009-07-27 21:33:55

by [email protected]

[permalink] [raw]
Subject: Re: [PATCH] svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet

On Tue, Aug 12, 2008 at 05:13:04PM -0500, Tom Tucker wrote:
> 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.

Thanks. Assuming this race has existed from the start (so it's not a
recent regression), and the consequences are no worse than a stall, I'm
inclined to queue this up for 2.6.32--but if I'm wrong about either of
those, we could try for 2.6.31 and/or stable.

--b.

>
> Signed-off-by: Tom Tucker <[email protected]>
>
> ---
> include/linux/sunrpc/svc_rdma.h | 1 -
> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 8 ++++----
> net/sunrpc/xprtrdma/svc_rdma_transport.c | 5 ++---
> 3 files changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
> index ef2e3a2..dc05b54 100644
> --- a/include/linux/sunrpc/svc_rdma.h
> +++ b/include/linux/sunrpc/svc_rdma.h
> @@ -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 */
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> index b4b17f4..74de31a 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> @@ -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,
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> index 19ddc38..900cb69 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> @@ -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;

2009-07-27 21:35:40

by [email protected]

[permalink] [raw]
Subject: Re: [PATCH] svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet

On Mon, Jul 27, 2009 at 05:33:55PM -0400, bfields wrote:
> On Tue, Aug 12, 2008 at 05:13:04PM -0500, Tom Tucker wrote:
> > 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.
>
> Thanks. Assuming this race has existed from the start (so it's not a
> recent regression), and the consequences are no worse than a stall, I'm
> inclined to queue this up for 2.6.32--but if I'm wrong about either of
> those, we could try for 2.6.31 and/or stable.

Erp, cripes, sorry--only just noticed all this mail seems to have been
delayed a year! OK....--b.

>
> --b.
>
> >
> > Signed-off-by: Tom Tucker <[email protected]>
> >
> > ---
> > include/linux/sunrpc/svc_rdma.h | 1 -
> > net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 8 ++++----
> > net/sunrpc/xprtrdma/svc_rdma_transport.c | 5 ++---
> > 3 files changed, 6 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
> > index ef2e3a2..dc05b54 100644
> > --- a/include/linux/sunrpc/svc_rdma.h
> > +++ b/include/linux/sunrpc/svc_rdma.h
> > @@ -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 */
> > diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > index b4b17f4..74de31a 100644
> > --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> > @@ -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,
> > diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> > index 19ddc38..900cb69 100644
> > --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
> > +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> > @@ -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;

2009-07-27 22:06:10

by Tom Tucker

[permalink] [raw]
Subject: Re: [PATCH] svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet

Please disregard this mail! I fixed a relayhost parameter in a lab
machine and this queued mail was sent. My apologies.

Tom

J. Bruce Fields wrote:
> On Mon, Jul 27, 2009 at 05:33:55PM -0400, bfields wrote:
>
>> On Tue, Aug 12, 2008 at 05:13:04PM -0500, Tom Tucker wrote:
>>
>>> 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.
>>>
>> Thanks. Assuming this race has existed from the start (so it's not a
>> recent regression), and the consequences are no worse than a stall, I'm
>> inclined to queue this up for 2.6.32--but if I'm wrong about either of
>> those, we could try for 2.6.31 and/or stable.
>>
>
> Erp, cripes, sorry--only just noticed all this mail seems to have been
> delayed a year! OK....--b.
>
>
>> --b.
>>
>>
>>> Signed-off-by: Tom Tucker <[email protected]>
>>>
>>> ---
>>> include/linux/sunrpc/svc_rdma.h | 1 -
>>> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 8 ++++----
>>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 5 ++---
>>> 3 files changed, 6 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
>>> index ef2e3a2..dc05b54 100644
>>> --- a/include/linux/sunrpc/svc_rdma.h
>>> +++ b/include/linux/sunrpc/svc_rdma.h
>>> @@ -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 */
>>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>> index b4b17f4..74de31a 100644
>>> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>> @@ -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,
>>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>> index 19ddc38..900cb69 100644
>>> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>> @@ -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;
>>>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>


2009-07-27 22:09:32

by [email protected]

[permalink] [raw]
Subject: Re: [PATCH] svcrdma: Fix race between svc_rdma_recvfrom thread and the dto_tasklet

On Mon, Jul 27, 2009 at 04:43:21PM -0500, Tom Tucker wrote:
> Please disregard this mail! I fixed a relayhost parameter in a lab
> machine and this queued mail was sent. My apologies.

No problem! I didn't recognize that first patch, but then got to the
following series and said hey, wait a minute, we already did this....

--b.

>
> Tom
>
> J. Bruce Fields wrote:
>> On Mon, Jul 27, 2009 at 05:33:55PM -0400, bfields wrote:
>>
>>> On Tue, Aug 12, 2008 at 05:13:04PM -0500, Tom Tucker wrote:
>>>
>>>> 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.
>>>>
>>> Thanks. Assuming this race has existed from the start (so it's not a
>>> recent regression), and the consequences are no worse than a stall, I'm
>>> inclined to queue this up for 2.6.32--but if I'm wrong about either of
>>> those, we could try for 2.6.31 and/or stable.
>>>
>>
>> Erp, cripes, sorry--only just noticed all this mail seems to have been
>> delayed a year! OK....--b.
>>
>>
>>> --b.
>>>
>>>
>>>> Signed-off-by: Tom Tucker <[email protected]>
>>>>
>>>> ---
>>>> include/linux/sunrpc/svc_rdma.h | 1 -
>>>> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 8 ++++----
>>>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 5 ++---
>>>> 3 files changed, 6 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
>>>> index ef2e3a2..dc05b54 100644
>>>> --- a/include/linux/sunrpc/svc_rdma.h
>>>> +++ b/include/linux/sunrpc/svc_rdma.h
>>>> @@ -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 */
>>>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>>> index b4b17f4..74de31a 100644
>>>> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>>> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>>>> @@ -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,
>>>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>>> index 19ddc38..900cb69 100644
>>>> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>>> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>>>> @@ -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;
>>>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>> the body of a message to [email protected]
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>
>