diff mbox series

[2/3] SUNRPC: Fix trace_xprt_transmit_queued()

Message ID 161721134086.515091.16531400209127881709.stgit@manet.1015granger.net (mailing list archive)
State New
Headers show
Series [1/3] SUNRPC: Move fault injection call sites | expand

Commit Message

Chuck Lever III March 31, 2021, 5:22 p.m. UTC
This tracepoint can crash when dereferencing snd_task because
when some transports connect, they put a cookie in that field
instead of a pointer to an rpc_task.

BUG: KASAN: use-after-free in trace_event_raw_event_xprt_writelock_event+0x141/0x18e [sunrpc]
Read of size 2 at addr ffff8881a83bd3a0 by task git/331872

CPU: 11 PID: 331872 Comm: git Tainted: G S                5.12.0-rc2-00007-g3ab6e585a7f9 #1453
Hardware name: Supermicro SYS-6028R-T/X10DRi, BIOS 1.1a 10/16/2015
Call Trace:
 dump_stack+0x9c/0xcf
 print_address_description.constprop.0+0x18/0x239
 kasan_report+0x174/0x1b0
 trace_event_raw_event_xprt_writelock_event+0x141/0x18e [sunrpc]
 xprt_prepare_transmit+0x8e/0xc1 [sunrpc]
 call_transmit+0x4d/0xc6 [sunrpc]

Fixes: 9ce07ae5eb1d ("SUNRPC: Replace dprintk() call site in xprt_prepare_transmit")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/trace/events/sunrpc.h |   35 ++++++++++++++++++++++++++++++++++-
 net/sunrpc/xprt.c             |    2 +-
 2 files changed, 35 insertions(+), 2 deletions(-)

Comments

Trond Myklebust March 31, 2021, 5:52 p.m. UTC | #1
On Wed, 2021-03-31 at 13:22 -0400, Chuck Lever wrote:
> This tracepoint can crash when dereferencing snd_task because
> when some transports connect, they put a cookie in that field
> instead of a pointer to an rpc_task.
> 
> BUG: KASAN: use-after-free in
> trace_event_raw_event_xprt_writelock_event+0x141/0x18e [sunrpc]
> Read of size 2 at addr ffff8881a83bd3a0 by task git/331872
> 
> CPU: 11 PID: 331872 Comm: git Tainted: G S                5.12.0-rc2-
> 00007-g3ab6e585a7f9 #1453
> Hardware name: Supermicro SYS-6028R-T/X10DRi, BIOS 1.1a 10/16/2015
> Call Trace:
>  dump_stack+0x9c/0xcf
>  print_address_description.constprop.0+0x18/0x239
>  kasan_report+0x174/0x1b0
>  trace_event_raw_event_xprt_writelock_event+0x141/0x18e [sunrpc]
>  xprt_prepare_transmit+0x8e/0xc1 [sunrpc]
>  call_transmit+0x4d/0xc6 [sunrpc]
> 
> Fixes: 9ce07ae5eb1d ("SUNRPC: Replace dprintk() call site in
> xprt_prepare_transmit")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  include/trace/events/sunrpc.h |   35
> ++++++++++++++++++++++++++++++++++-
>  net/sunrpc/xprt.c             |    2 +-
>  2 files changed, 35 insertions(+), 2 deletions(-)
> 
> diff --git a/include/trace/events/sunrpc.h
> b/include/trace/events/sunrpc.h
> index 036eb1f5c133..690988530d60 100644
> --- a/include/trace/events/sunrpc.h
> +++ b/include/trace/events/sunrpc.h
> @@ -1141,7 +1141,40 @@ DECLARE_EVENT_CLASS(xprt_writelock_event,
>  
>  DEFINE_WRITELOCK_EVENT(reserve_xprt);
>  DEFINE_WRITELOCK_EVENT(release_xprt);
> -DEFINE_WRITELOCK_EVENT(transmit_queued);
> +
> +TRACE_EVENT(xprt_transmit_queued,
> +       TP_PROTO(
> +               const struct rpc_task *task
> +       ),
> +
> +       TP_ARGS(task),
> +
> +       TP_STRUCT__entry(
> +               __field(unsigned int, task_id)
> +               __field(unsigned int, client_id)
> +               __field(unsigned long, runstate)
> +               __field(u32, xid)
> +               __field(int, status)
> +               __field(unsigned short, flags)
> +       ),
> +
> +       TP_fast_assign(
> +               __entry->task_id = task->tk_pid;
> +               __entry->client_id =
> +                       task->tk_client ? task->tk_client->cl_clid :
> -1;
> +               __entry->runstate = task->tk_runstate;
> +               __entry->xid = be32_to_cpu(task->tk_rqstp->rq_xid);
> +               __entry->status = task->tk_status;
> +               __entry->flags = task->tk_flags;
> +       ),
> +
> +       TP_printk("task:%u@%u xid=0x%08x flags=%s runstate=%s
> status=%d",
> +               __entry->task_id, __entry->client_id, __entry->xid,
> +               rpc_show_task_flags(__entry->flags),
> +               rpc_show_runstate(__entry->runstate),
> +               __entry->status
> +       )
> +);
>  
>  DECLARE_EVENT_CLASS(xprt_cong_event,
>         TP_PROTO(
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index d616b93751d8..b694af4504c4 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -1469,7 +1469,7 @@ bool xprt_prepare_transmit(struct rpc_task
> *task)
>         struct rpc_xprt *xprt = req->rq_xprt;
>  
>         if (!xprt_lock_write(xprt, task)) {
> -               trace_xprt_transmit_queued(xprt, task);
> +               trace_xprt_transmit_queued(task);

Why do we need this tracepoint? The event we're logging is just
"grabbing the transport write lock failed due to external
circumstances".
 
>                 /* Race breaker: someone may have transmitted us */
>                 if (!test_bit(RPC_TASK_NEED_XMIT, &task-
> >tk_runstate))
> 
>
Chuck Lever III March 31, 2021, 7:22 p.m. UTC | #2
> On Mar 31, 2021, at 1:52 PM, Trond Myklebust <trondmy@hammerspace.com> wrote:
> 
> On Wed, 2021-03-31 at 13:22 -0400, Chuck Lever wrote:
>> This tracepoint can crash when dereferencing snd_task because
>> when some transports connect, they put a cookie in that field
>> instead of a pointer to an rpc_task.
>> 
>> BUG: KASAN: use-after-free in
>> trace_event_raw_event_xprt_writelock_event+0x141/0x18e [sunrpc]
>> Read of size 2 at addr ffff8881a83bd3a0 by task git/331872
>> 
>> CPU: 11 PID: 331872 Comm: git Tainted: G S                5.12.0-rc2-
>> 00007-g3ab6e585a7f9 #1453
>> Hardware name: Supermicro SYS-6028R-T/X10DRi, BIOS 1.1a 10/16/2015
>> Call Trace:
>>  dump_stack+0x9c/0xcf
>>  print_address_description.constprop.0+0x18/0x239
>>  kasan_report+0x174/0x1b0
>>  trace_event_raw_event_xprt_writelock_event+0x141/0x18e [sunrpc]
>>  xprt_prepare_transmit+0x8e/0xc1 [sunrpc]
>>  call_transmit+0x4d/0xc6 [sunrpc]
>> 
>> Fixes: 9ce07ae5eb1d ("SUNRPC: Replace dprintk() call site in
>> xprt_prepare_transmit")
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>> ---
>>  include/trace/events/sunrpc.h |   35
>> ++++++++++++++++++++++++++++++++++-
>>  net/sunrpc/xprt.c             |    2 +-
>>  2 files changed, 35 insertions(+), 2 deletions(-)
>> 
>> diff --git a/include/trace/events/sunrpc.h
>> b/include/trace/events/sunrpc.h
>> index 036eb1f5c133..690988530d60 100644
>> --- a/include/trace/events/sunrpc.h
>> +++ b/include/trace/events/sunrpc.h
>> @@ -1141,7 +1141,40 @@ DECLARE_EVENT_CLASS(xprt_writelock_event,
>>  
>>  DEFINE_WRITELOCK_EVENT(reserve_xprt);
>>  DEFINE_WRITELOCK_EVENT(release_xprt);
>> -DEFINE_WRITELOCK_EVENT(transmit_queued);
>> +
>> +TRACE_EVENT(xprt_transmit_queued,
>> +       TP_PROTO(
>> +               const struct rpc_task *task
>> +       ),
>> +
>> +       TP_ARGS(task),
>> +
>> +       TP_STRUCT__entry(
>> +               __field(unsigned int, task_id)
>> +               __field(unsigned int, client_id)
>> +               __field(unsigned long, runstate)
>> +               __field(u32, xid)
>> +               __field(int, status)
>> +               __field(unsigned short, flags)
>> +       ),
>> +
>> +       TP_fast_assign(
>> +               __entry->task_id = task->tk_pid;
>> +               __entry->client_id =
>> +                       task->tk_client ? task->tk_client->cl_clid :
>> -1;
>> +               __entry->runstate = task->tk_runstate;
>> +               __entry->xid = be32_to_cpu(task->tk_rqstp->rq_xid);
>> +               __entry->status = task->tk_status;
>> +               __entry->flags = task->tk_flags;
>> +       ),
>> +
>> +       TP_printk("task:%u@%u xid=0x%08x flags=%s runstate=%s
>> status=%d",
>> +               __entry->task_id, __entry->client_id, __entry->xid,
>> +               rpc_show_task_flags(__entry->flags),
>> +               rpc_show_runstate(__entry->runstate),
>> +               __entry->status
>> +       )
>> +);
>>  
>>  DECLARE_EVENT_CLASS(xprt_cong_event,
>>         TP_PROTO(
>> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
>> index d616b93751d8..b694af4504c4 100644
>> --- a/net/sunrpc/xprt.c
>> +++ b/net/sunrpc/xprt.c
>> @@ -1469,7 +1469,7 @@ bool xprt_prepare_transmit(struct rpc_task
>> *task)
>>         struct rpc_xprt *xprt = req->rq_xprt;
>>  
>>         if (!xprt_lock_write(xprt, task)) {
>> -               trace_xprt_transmit_queued(xprt, task);
>> +               trace_xprt_transmit_queued(task);
> 
> Why do we need this tracepoint? The event we're logging is just
> "grabbing the transport write lock failed due to external
> circumstances".

This tracepoint records the decision to queue rather than send immediately.

You can count the number of these to get an idea whether the transport
is backed up.

You can trigger on this event if you want to capture the events that
lead up to queuing a request.

You can see whether the client logic is making the right choice when
congestion control is in play.


>>                 /* Race breaker: someone may have transmitted us */
>>                 if (!test_bit(RPC_TASK_NEED_XMIT, &task-
>>> tk_runstate))
>> 
>> 
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com

--
Chuck Lever
Trond Myklebust March 31, 2021, 7:40 p.m. UTC | #3
On Wed, 2021-03-31 at 19:22 +0000, Chuck Lever III wrote:
> 
> 
> > On Mar 31, 2021, at 1:52 PM, Trond Myklebust <
> > trondmy@hammerspace.com> wrote:
> > 
> > On Wed, 2021-03-31 at 13:22 -0400, Chuck Lever wrote:
> > > This tracepoint can crash when dereferencing snd_task because
> > > when some transports connect, they put a cookie in that field
> > > instead of a pointer to an rpc_task.
> > > 
> > > BUG: KASAN: use-after-free in
> > > trace_event_raw_event_xprt_writelock_event+0x141/0x18e [sunrpc]
> > > Read of size 2 at addr ffff8881a83bd3a0 by task git/331872
> > > 
> > > CPU: 11 PID: 331872 Comm: git Tainted: G S                5.12.0-
> > > rc2-
> > > 00007-g3ab6e585a7f9 #1453
> > > Hardware name: Supermicro SYS-6028R-T/X10DRi, BIOS 1.1a
> > > 10/16/2015
> > > Call Trace:
> > >  dump_stack+0x9c/0xcf
> > >  print_address_description.constprop.0+0x18/0x239
> > >  kasan_report+0x174/0x1b0
> > >  trace_event_raw_event_xprt_writelock_event+0x141/0x18e [sunrpc]
> > >  xprt_prepare_transmit+0x8e/0xc1 [sunrpc]
> > >  call_transmit+0x4d/0xc6 [sunrpc]
> > > 
> > > Fixes: 9ce07ae5eb1d ("SUNRPC: Replace dprintk() call site in
> > > xprt_prepare_transmit")
> > > Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> > > ---
> > >  include/trace/events/sunrpc.h |   35
> > > ++++++++++++++++++++++++++++++++++-
> > >  net/sunrpc/xprt.c             |    2 +-
> > >  2 files changed, 35 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/trace/events/sunrpc.h
> > > b/include/trace/events/sunrpc.h
> > > index 036eb1f5c133..690988530d60 100644
> > > --- a/include/trace/events/sunrpc.h
> > > +++ b/include/trace/events/sunrpc.h
> > > @@ -1141,7 +1141,40 @@ DECLARE_EVENT_CLASS(xprt_writelock_event,
> > >  
> > >  DEFINE_WRITELOCK_EVENT(reserve_xprt);
> > >  DEFINE_WRITELOCK_EVENT(release_xprt);
> > > -DEFINE_WRITELOCK_EVENT(transmit_queued);
> > > +
> > > +TRACE_EVENT(xprt_transmit_queued,
> > > +       TP_PROTO(
> > > +               const struct rpc_task *task
> > > +       ),
> > > +
> > > +       TP_ARGS(task),
> > > +
> > > +       TP_STRUCT__entry(
> > > +               __field(unsigned int, task_id)
> > > +               __field(unsigned int, client_id)
> > > +               __field(unsigned long, runstate)
> > > +               __field(u32, xid)
> > > +               __field(int, status)
> > > +               __field(unsigned short, flags)
> > > +       ),
> > > +
> > > +       TP_fast_assign(
> > > +               __entry->task_id = task->tk_pid;
> > > +               __entry->client_id =
> > > +                       task->tk_client ? task->tk_client-
> > > >cl_clid :
> > > -1;
> > > +               __entry->runstate = task->tk_runstate;
> > > +               __entry->xid = be32_to_cpu(task->tk_rqstp-
> > > >rq_xid);
> > > +               __entry->status = task->tk_status;
> > > +               __entry->flags = task->tk_flags;
> > > +       ),
> > > +
> > > +       TP_printk("task:%u@%u xid=0x%08x flags=%s runstate=%s
> > > status=%d",
> > > +               __entry->task_id, __entry->client_id, __entry-
> > > >xid,
> > > +               rpc_show_task_flags(__entry->flags),
> > > +               rpc_show_runstate(__entry->runstate),
> > > +               __entry->status
> > > +       )
> > > +);
> > >  
> > >  DECLARE_EVENT_CLASS(xprt_cong_event,
> > >         TP_PROTO(
> > > diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> > > index d616b93751d8..b694af4504c4 100644
> > > --- a/net/sunrpc/xprt.c
> > > +++ b/net/sunrpc/xprt.c
> > > @@ -1469,7 +1469,7 @@ bool xprt_prepare_transmit(struct rpc_task
> > > *task)
> > >         struct rpc_xprt *xprt = req->rq_xprt;
> > >  
> > >         if (!xprt_lock_write(xprt, task)) {
> > > -               trace_xprt_transmit_queued(xprt, task);
> > > +               trace_xprt_transmit_queued(task);
> > 
> > Why do we need this tracepoint? The event we're logging is just
> > "grabbing the transport write lock failed due to external
> > circumstances".
> 
> This tracepoint records the decision to queue rather than send
> immediately.

The request is already queued before we call xprt_prepare_transmit().

The decision being made here is whether or not we can move forward with
driving the bind or connect or transmission. This tracepoint just
records the case where something is blocking this specific rpc_task
from doing so.

> You can count the number of these to get an idea whether the
> transport
> is backed up.
> 
> You can trigger on this event if you want to capture the events that
> lead up to queuing a request.

The lock can be unavailable simply because some other rpc_task is
already in the process of draining the queue.

If you want to find out if transmission is actually blocked, you're
better off triggering on the event that caused the blockage (either a
disconnect or a failure to reconnect or rebind). This tracepoint is
going to cause way too many false positives to be of any use for
tracing blockage.

> You can see whether the client logic is making the right choice when
> congestion control is in play.

Don't we already have a tracepoint in xprt_reserve_xprt_cong() for
this?

> 
> 
> > >                 /* Race breaker: someone may have transmitted us
> > > */
> > >                 if (!test_bit(RPC_TASK_NEED_XMIT, &task-
> > > > tk_runstate))
> > > 
> > > 
> > 
> > -- 
> > Trond Myklebust
> > Linux NFS client maintainer, Hammerspace
> > trond.myklebust@hammerspace.com
> 
> --
> Chuck Lever
> 
> 
>
diff mbox series

Patch

diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 036eb1f5c133..690988530d60 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -1141,7 +1141,40 @@  DECLARE_EVENT_CLASS(xprt_writelock_event,
 
 DEFINE_WRITELOCK_EVENT(reserve_xprt);
 DEFINE_WRITELOCK_EVENT(release_xprt);
-DEFINE_WRITELOCK_EVENT(transmit_queued);
+
+TRACE_EVENT(xprt_transmit_queued,
+	TP_PROTO(
+		const struct rpc_task *task
+	),
+
+	TP_ARGS(task),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, task_id)
+		__field(unsigned int, client_id)
+		__field(unsigned long, runstate)
+		__field(u32, xid)
+		__field(int, status)
+		__field(unsigned short, flags)
+	),
+
+	TP_fast_assign(
+		__entry->task_id = task->tk_pid;
+		__entry->client_id =
+			task->tk_client ? task->tk_client->cl_clid : -1;
+		__entry->runstate = task->tk_runstate;
+		__entry->xid = be32_to_cpu(task->tk_rqstp->rq_xid);
+		__entry->status = task->tk_status;
+		__entry->flags = task->tk_flags;
+	),
+
+	TP_printk("task:%u@%u xid=0x%08x flags=%s runstate=%s status=%d",
+		__entry->task_id, __entry->client_id, __entry->xid,
+		rpc_show_task_flags(__entry->flags),
+		rpc_show_runstate(__entry->runstate),
+		__entry->status
+	)
+);
 
 DECLARE_EVENT_CLASS(xprt_cong_event,
 	TP_PROTO(
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index d616b93751d8..b694af4504c4 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1469,7 +1469,7 @@  bool xprt_prepare_transmit(struct rpc_task *task)
 	struct rpc_xprt	*xprt = req->rq_xprt;
 
 	if (!xprt_lock_write(xprt, task)) {
-		trace_xprt_transmit_queued(xprt, task);
+		trace_xprt_transmit_queued(task);
 
 		/* Race breaker: someone may have transmitted us */
 		if (!test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))