Commit 286c171b authored by Dominique Martinet's avatar Dominique Martinet Committed by Dominique Martinet
Browse files

9p fid refcount: add a 9p_fid_ref tracepoint 

This adds a tracepoint event for 9p fid lifecycle tracing: when a fid
is created, its reference count increased/decreased, and freed.
The new 9p_fid_ref tracepoint should help anyone wishing to debug any
fid problem such as missing clunk (destroy) or use-after-free.

Link: https://lkml.kernel.org/r/20220612085330.1451496-6-asmadeus@codewreck.org


Signed-off-by: default avatarDominique Martinet <asmadeus@codewreck.org>
parent b48dbb99

include/net/9p/client.h

+13 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 


#include <linux/utsname.h>

#include <linux/idr.h>

#include <linux/tracepoint-defs.h>



/* Number of requests per row */

#define P9_ROW_MAXTAG 255
@@ -237,6 +238,12 @@ static inline int p9_req_try_get(struct p9_req_t *r) 


int p9_req_put(struct p9_req_t *r);



/* We cannot have the real tracepoints in header files,

 * use a wrapper function */

DECLARE_TRACEPOINT(9p_fid_ref);

void do_trace_9p_fid_get(struct p9_fid *fid);

void do_trace_9p_fid_put(struct p9_fid *fid);



/* fid reference counting helpers:

 *  - fids used for any length of time should always be referenced through

 *    p9_fid_get(), and released with p9_fid_put()
@@ -249,6 +256,9 @@ int p9_req_put(struct p9_req_t *r); 
 */

static inline struct p9_fid *p9_fid_get(struct p9_fid *fid)

{

	if (tracepoint_enabled(9p_fid_ref))

		do_trace_9p_fid_get(fid);



	refcount_inc(&fid->count);



	return fid;
@@ -259,6 +269,9 @@ static inline int p9_fid_put(struct p9_fid *fid) 
	if (!fid || IS_ERR(fid))

		return 0;



	if (tracepoint_enabled(9p_fid_ref))

		do_trace_9p_fid_put(fid);



	if (!refcount_dec_and_test(&fid->count))

		return 0;

include/trace/events/9p.h

+48 −0
Original line number Diff line number Diff line
@@ -77,6 +77,13 @@ 
		EM( P9_TWSTAT,		"P9_TWSTAT" )			\

		EMe(P9_RWSTAT,		"P9_RWSTAT" )





#define P9_FID_REFTYPE							\

		EM( P9_FID_REF_CREATE,	"create " )			\

		EM( P9_FID_REF_GET,	"get    " )			\

		EM( P9_FID_REF_PUT,	"put    " )			\

		EMe(P9_FID_REF_DESTROY,	"destroy" )



/* Define EM() to export the enums to userspace via TRACE_DEFINE_ENUM() */

#undef EM

#undef EMe
@@ -84,6 +91,21 @@ 
#define EMe(a, b)	TRACE_DEFINE_ENUM(a);



P9_MSG_T

P9_FID_REFTYPE



/* And also use EM/EMe to define helper enums -- once */

#ifndef __9P_DECLARE_TRACE_ENUMS_ONLY_ONCE

#define __9P_DECLARE_TRACE_ENUMS_ONLY_ONCE

#undef EM

#undef EMe

#define EM(a, b)	a,

#define EMe(a, b)	a



enum p9_fid_reftype {

	P9_FID_REFTYPE

} __mode(byte);



#endif



/*

 * Now redefine the EM() and EMe() macros to map the enums to the strings
@@ -96,6 +118,8 @@ P9_MSG_T 


#define show_9p_op(type)						\

	__print_symbolic(type, P9_MSG_T)

#define show_9p_fid_reftype(type)					\

	__print_symbolic(type, P9_FID_REFTYPE)



TRACE_EVENT(9p_client_req,

	    TP_PROTO(struct p9_client *clnt, int8_t type, int tag),
@@ -168,6 +192,30 @@ TRACE_EVENT(9p_protocol_dump, 
		      __entry->tag, 0, __entry->line, 16, __entry->line + 16)

 );





TRACE_EVENT(9p_fid_ref,

	    TP_PROTO(struct p9_fid *fid, __u8 type),



	    TP_ARGS(fid, type),



	    TP_STRUCT__entry(

		    __field(	int,	fid		)

		    __field(	int,	refcount	)

		    __field(	__u8, type	)

		    ),



	    TP_fast_assign(

		    __entry->fid = fid->fid;

		    __entry->refcount = refcount_read(&fid->count);

		    __entry->type = type;

		    ),



	    TP_printk("%s fid %d, refcount %d",

		      show_9p_fid_reftype(__entry->type),

		      __entry->fid, __entry->refcount)

);





#endif /* _TRACE_9P_H */



/* This part must be outside protection */

net/9p/client.c

+19 −1
Original line number Diff line number Diff line
@@ -907,8 +907,10 @@ static struct p9_fid *p9_fid_create(struct p9_client *clnt) 
			    GFP_NOWAIT);

	spin_unlock_irq(&clnt->lock);

	idr_preload_end();

	if (!ret)

	if (!ret) {

		trace_9p_fid_ref(fid, P9_FID_REF_CREATE);

		return fid;

	}



	kfree(fid);

	return NULL;
@@ -920,6 +922,7 @@ static void p9_fid_destroy(struct p9_fid *fid) 
	unsigned long flags;



	p9_debug(P9_DEBUG_FID, "fid %d\n", fid->fid);

	trace_9p_fid_ref(fid, P9_FID_REF_DESTROY);

	clnt = fid->clnt;

	spin_lock_irqsave(&clnt->lock, flags);

	idr_remove(&clnt->fids, fid->fid);
@@ -928,6 +931,21 @@ static void p9_fid_destroy(struct p9_fid *fid) 
	kfree(fid);

}



/* We also need to export tracepoint symbols for tracepoint_enabled() */

EXPORT_TRACEPOINT_SYMBOL(9p_fid_ref);



void do_trace_9p_fid_get(struct p9_fid *fid)

{

	trace_9p_fid_ref(fid, P9_FID_REF_GET);

}

EXPORT_SYMBOL(do_trace_9p_fid_get);



void do_trace_9p_fid_put(struct p9_fid *fid)

{

	trace_9p_fid_ref(fid, P9_FID_REF_PUT);

}

EXPORT_SYMBOL(do_trace_9p_fid_put);



static int p9_client_version(struct p9_client *c)

{

	int err = 0;