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Subject[PATCH 2/2] afs: Fix access after dec in put functions
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Date
Reference-putting functions should not access the object being put after
decrementing the refcount unless they reduce the refcount to zero.

Fix a couple of instances of this in afs by copying the information to be
logged by tracepoint to local variables before doing the decrement.

Fixes: 341f741f04be ("afs: Refcount the afs_call struct")
Fixes: 452181936931 ("afs: Trace afs_server usage")
Fixes: 977e5f8ed0ab ("afs: Split the usage count on struct afs_server")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
---

fs/afs/cmservice.c | 2 +-
fs/afs/rxrpc.c | 11 ++++++-----
fs/afs/server.c | 22 +++++++++++++---------
include/trace/events/afs.h | 12 ++++++------
4 files changed, 26 insertions(+), 21 deletions(-)

diff --git a/fs/afs/cmservice.c b/fs/afs/cmservice.c
index cedd627e1fae..0a090d614e76 100644
--- a/fs/afs/cmservice.c
+++ b/fs/afs/cmservice.c
@@ -212,7 +212,7 @@ static void SRXAFSCB_CallBack(struct work_struct *work)
* to maintain cache coherency.
*/
if (call->server) {
- trace_afs_server(call->server,
+ trace_afs_server(call->server->debug_id,
refcount_read(&call->server->ref),
atomic_read(&call->server->active),
afs_server_trace_callback);
diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index d9acc43cb6f0..d5c4785c862d 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -152,7 +152,7 @@ static struct afs_call *afs_alloc_call(struct afs_net *net,
call->iter = &call->def_iter;

o = atomic_inc_return(&net->nr_outstanding_calls);
- trace_afs_call(call, afs_call_trace_alloc, 1, o,
+ trace_afs_call(call->debug_id, afs_call_trace_alloc, 1, o,
__builtin_return_address(0));
return call;
}
@@ -163,12 +163,13 @@ static struct afs_call *afs_alloc_call(struct afs_net *net,
void afs_put_call(struct afs_call *call)
{
struct afs_net *net = call->net;
+ unsigned int debug_id = call->debug_id;
bool zero;
int r, o;

zero = __refcount_dec_and_test(&call->ref, &r);
o = atomic_read(&net->nr_outstanding_calls);
- trace_afs_call(call, afs_call_trace_put, r - 1, o,
+ trace_afs_call(debug_id, afs_call_trace_put, r - 1, o,
__builtin_return_address(0));

if (zero) {
@@ -186,7 +187,7 @@ void afs_put_call(struct afs_call *call)
afs_put_addrlist(call->alist);
kfree(call->request);

- trace_afs_call(call, afs_call_trace_free, 0, o,
+ trace_afs_call(call->debug_id, afs_call_trace_free, 0, o,
__builtin_return_address(0));
kfree(call);

@@ -203,7 +204,7 @@ static struct afs_call *afs_get_call(struct afs_call *call,

__refcount_inc(&call->ref, &r);

- trace_afs_call(call, why, r + 1,
+ trace_afs_call(call->debug_id, why, r + 1,
atomic_read(&call->net->nr_outstanding_calls),
__builtin_return_address(0));
return call;
@@ -677,7 +678,7 @@ static void afs_wake_up_async_call(struct sock *sk, struct rxrpc_call *rxcall,
call->need_attention = true;

if (__refcount_inc_not_zero(&call->ref, &r)) {
- trace_afs_call(call, afs_call_trace_wake, r + 1,
+ trace_afs_call(call->debug_id, afs_call_trace_wake, r + 1,
atomic_read(&call->net->nr_outstanding_calls),
__builtin_return_address(0));

diff --git a/fs/afs/server.c b/fs/afs/server.c
index ffed828622b6..bca4b4c55c14 100644
--- a/fs/afs/server.c
+++ b/fs/afs/server.c
@@ -243,7 +243,7 @@ static struct afs_server *afs_alloc_server(struct afs_cell *cell,
server->rtt = UINT_MAX;

afs_inc_servers_outstanding(net);
- trace_afs_server(server, 1, 1, afs_server_trace_alloc);
+ trace_afs_server(server->debug_id, 1, 1, afs_server_trace_alloc);
_leave(" = %p", server);
return server;

@@ -352,10 +352,12 @@ void afs_servers_timer(struct timer_list *timer)
struct afs_server *afs_get_server(struct afs_server *server,
enum afs_server_trace reason)
{
+ unsigned int a;
int r;

__refcount_inc(&server->ref, &r);
- trace_afs_server(server, r + 1, atomic_read(&server->active), reason);
+ a = atomic_read(&server->active);
+ trace_afs_server(server->debug_id, r + 1, a, reason);
return server;
}

@@ -372,7 +374,7 @@ static struct afs_server *afs_maybe_use_server(struct afs_server *server,
return NULL;

a = atomic_inc_return(&server->active);
- trace_afs_server(server, r + 1, a, reason);
+ trace_afs_server(server->debug_id, r + 1, a, reason);
return server;
}

@@ -387,7 +389,7 @@ struct afs_server *afs_use_server(struct afs_server *server, enum afs_server_tra
__refcount_inc(&server->ref, &r);
a = atomic_inc_return(&server->active);

- trace_afs_server(server, r + 1, a, reason);
+ trace_afs_server(server->debug_id, r + 1, a, reason);
return server;
}

@@ -397,14 +399,16 @@ struct afs_server *afs_use_server(struct afs_server *server, enum afs_server_tra
void afs_put_server(struct afs_net *net, struct afs_server *server,
enum afs_server_trace reason)
{
+ unsigned int a;
bool zero;
int r;

if (!server)
return;

+ a = atomic_inc_return(&server->active);
zero = __refcount_dec_and_test(&server->ref, &r);
- trace_afs_server(server, r - 1, atomic_read(&server->active), reason);
+ trace_afs_server(server->debug_id, r - 1, a, reason);
if (unlikely(zero))
__afs_put_server(net, server);
}
@@ -441,7 +445,7 @@ static void afs_server_rcu(struct rcu_head *rcu)
{
struct afs_server *server = container_of(rcu, struct afs_server, rcu);

- trace_afs_server(server, refcount_read(&server->ref),
+ trace_afs_server(server->debug_id, refcount_read(&server->ref),
atomic_read(&server->active), afs_server_trace_free);
afs_put_addrlist(rcu_access_pointer(server->addresses));
kfree(server);
@@ -492,7 +496,7 @@ static void afs_gc_servers(struct afs_net *net, struct afs_server *gc_list)

active = atomic_read(&server->active);
if (active == 0) {
- trace_afs_server(server, refcount_read(&server->ref),
+ trace_afs_server(server->debug_id, refcount_read(&server->ref),
active, afs_server_trace_gc);
next = rcu_dereference_protected(
server->uuid_next, lockdep_is_held(&net->fs_lock.lock));
@@ -558,7 +562,7 @@ void afs_manage_servers(struct work_struct *work)
_debug("manage %pU %u", &server->uuid, active);

if (purging) {
- trace_afs_server(server, refcount_read(&server->ref),
+ trace_afs_server(server->debug_id, refcount_read(&server->ref),
active, afs_server_trace_purging);
if (active != 0)
pr_notice("Can't purge s=%08x\n", server->debug_id);
@@ -638,7 +642,7 @@ static noinline bool afs_update_server_record(struct afs_operation *op,

_enter("");

- trace_afs_server(server, refcount_read(&server->ref),
+ trace_afs_server(server->debug_id, refcount_read(&server->ref),
atomic_read(&server->active),
afs_server_trace_update);

diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index aa60f42a9763..e9d412d19dbb 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -727,10 +727,10 @@ TRACE_EVENT(afs_cb_call,
);

TRACE_EVENT(afs_call,
- TP_PROTO(struct afs_call *call, enum afs_call_trace op,
+ TP_PROTO(unsigned int call_debug_id, enum afs_call_trace op,
int ref, int outstanding, const void *where),

- TP_ARGS(call, op, ref, outstanding, where),
+ TP_ARGS(call_debug_id, op, ref, outstanding, where),

TP_STRUCT__entry(
__field(unsigned int, call )
@@ -741,7 +741,7 @@ TRACE_EVENT(afs_call,
),

TP_fast_assign(
- __entry->call = call->debug_id;
+ __entry->call = call_debug_id;
__entry->op = op;
__entry->ref = ref;
__entry->outstanding = outstanding;
@@ -1433,10 +1433,10 @@ TRACE_EVENT(afs_cb_miss,
);

TRACE_EVENT(afs_server,
- TP_PROTO(struct afs_server *server, int ref, int active,
+ TP_PROTO(unsigned int server_debug_id, int ref, int active,
enum afs_server_trace reason),

- TP_ARGS(server, ref, active, reason),
+ TP_ARGS(server_debug_id, ref, active, reason),

TP_STRUCT__entry(
__field(unsigned int, server )
@@ -1446,7 +1446,7 @@ TRACE_EVENT(afs_server,
),

TP_fast_assign(
- __entry->server = server->debug_id;
+ __entry->server = server_debug_id;
__entry->ref = ref;
__entry->active = active;
__entry->reason = reason;

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