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9p fid refcount: add a 9p_fid_ref tracepoint

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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: Dominique Martinet <asmadeus@codewreck.org>
This commit is contained in:
Dominique Martinet 2022-06-13 08:32:06 +09:00 committed by Dominique Martinet
parent b48dbb998d
commit 286c171b86
3 changed files with 80 additions and 1 deletions
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13
include/net/9p/client.h
View File

@ -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;

48
include/trace/events/9p.h
View File

@ -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 */

20
net/9p/client.c
View File

@ -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;