linux-kernel - Re: [PATCH] sunrpc: Fix trace events to store data in the struct

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Message-ID: <CAHQdGtS4s6A=woScsXTwmnRmCSCEWcUNoUGMmXCF_E=+BBH73w@mail.gmail.com>
Date:	Tue, 24 Feb 2015 08:36:48 -0500
From:	Trond Myklebust <trond.myklebust@...marydata.com>
To:	James Hogan <james.hogan@...tec.com>
Cc:	Jeff Layton <jlayton@...marydata.com>,
	"J. Bruce Fields" <bfields@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Stable Tree Mailing List <stable@...r.kernel.org>
Subject: Re: [PATCH] sunrpc: Fix trace events to store data in the struct

On Tue, Feb 24, 2015 at 6:47 AM, James Hogan <james.hogan@...tec.com> wrote:
> Commit 83a712e0afef ("sunrpc: add some tracepoints around enqueue and
> dequeue of svc_xprt") merged in v3.19-rc1 added some new trace events,
> however a couple of them printed data from dereferenced pointers rather
> than storing the data in the struct. In general this isn't safe as the
> print may not happen until later when the data may have changed or been
> freed, and nor is it portable as userland won't have access to that
> other data in order to interpret the trace data itself.
>
> Fix by copying the data into the struct and printing from there.
>
> Fixes: 83a712e0afef ("sunrpc: add some tracepoints around enqueue ...")
> Signed-off-by: James Hogan <james.hogan@...tec.com>
> Cc: Jeff Layton <jlayton@...marydata.com>
> Cc: J. Bruce Fields <bfields@...hat.com>
> Cc: Trond Myklebust <trond.myklebust@...marydata.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: <stable@...r.kernel.org> # v3.19+
> ---
> Build tested only. Perhaps somebody familiar with the code could give it
> a spin to sanity check the trace output.
> ---
>  include/trace/events/sunrpc.h | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
> index b9c1dc6c825a..47dfcaebfaaf 100644
> --- a/include/trace/events/sunrpc.h
> +++ b/include/trace/events/sunrpc.h
> @@ -503,18 +503,22 @@ TRACE_EVENT(svc_xprt_do_enqueue,
>
>         TP_STRUCT__entry(
>                 __field(struct svc_xprt *, xprt)
> -               __field(struct svc_rqst *, rqst)
> +               __field_struct(struct sockaddr_storage, ss)
> +               __field(unsigned long, flags);
> +               __field(int, pid)
>         ),
>
>         TP_fast_assign(
>                 __entry->xprt = xprt;
> -               __entry->rqst = rqst;
> +               xprt ? memcpy(&__entry->ss, &xprt->xpt_remote, sizeof(__entry->ss)) : memset(&__entry->ss, 0, sizeof(__entry->ss));

How could xprt ever be NULL here, and even if it was, why the esoteric
C instead of a simple 'if' statement?

> +               __entry->flags = xprt ? xprt->xpt_flags : 0;
> +               __entry->pid = rqst ? rqst->rq_task->pid : 0;
>         ),
>
>         TP_printk("xprt=0x%p addr=%pIScp pid=%d flags=%s", __entry->xprt,
> -               (struct sockaddr *)&__entry->xprt->xpt_remote,
> -               __entry->rqst ? __entry->rqst->rq_task->pid : 0,
> -               show_svc_xprt_flags(__entry->xprt->xpt_flags))
> +               (struct sockaddr *)&__entry->ss,
> +               __entry->pid,
> +               show_svc_xprt_flags(__entry->flags))
>  );
>
>  TRACE_EVENT(svc_xprt_dequeue,
> @@ -562,17 +566,21 @@ TRACE_EVENT(svc_handle_xprt,
>
>         TP_STRUCT__entry(
>                 __field(struct svc_xprt *, xprt)
> +               __field_struct(struct sockaddr_storage, ss)
> +               __field(unsigned long, flags);
>                 __field(int, len)
>         ),
>
>         TP_fast_assign(
>                 __entry->xprt = xprt;
> +               xprt ? memcpy(&__entry->ss, &xprt->xpt_remote, sizeof(__entry->ss)) : memset(&__entry->ss, 0, sizeof(__entry->ss));

Ditto.

> +               __entry->flags = xprt ? xprt->xpt_flags : 0;
>                 __entry->len = len;
>         ),
>
>         TP_printk("xprt=0x%p addr=%pIScp len=%d flags=%s", __entry->xprt,
> -               (struct sockaddr *)&__entry->xprt->xpt_remote, __entry->len,
> -               show_svc_xprt_flags(__entry->xprt->xpt_flags))
> +               (struct sockaddr *)&__entry->ss, __entry->len,
> +               show_svc_xprt_flags(__entry->flags))
>  );
>  #endif /* _TRACE_SUNRPC_H */
>
> --
> 2.0.5
>



-- 
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@...marydata.com
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