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Message-ID: <1394602.1729162732@warthog.procyon.org.uk>
Date: Thu, 17 Oct 2024 11:58:52 +0100
From: David Howells <dhowells@...hat.com>
To: Christian Brauner <brauner@...nel.org>
Cc: dhowells@...hat.com, Marc Dionne <marc.dionne@...istor.com>,
linux-afs@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v2] afs: Fix lock recursion
afs_wake_up_async_call() can incur lock recursion. The problem is that it
is called from AF_RXRPC whilst holding the ->notify_lock, but it tries to
take a ref on the afs_call struct in order to pass it to a work queue - but
if the afs_call is already queued, we then have an extraneous ref that must
be put... calling afs_put_call() may call back down into AF_RXRPC through
rxrpc_kernel_shutdown_call(), however, which might try taking the
->notify_lock again.
This case isn't very common, however, so defer it to a workqueue. The oops
looks something like:
BUG: spinlock recursion on CPU#0, krxrpcio/7001/1646
lock: 0xffff888141399b30, .magic: dead4ead, .owner: krxrpcio/7001/1646, .owner_cpu: 0
CPU: 0 UID: 0 PID: 1646 Comm: krxrpcio/7001 Not tainted 6.12.0-rc2-build3+ #4351
Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
Call Trace:
<TASK>
dump_stack_lvl+0x47/0x70
do_raw_spin_lock+0x3c/0x90
rxrpc_kernel_shutdown_call+0x83/0xb0
afs_put_call+0xd7/0x180
rxrpc_notify_socket+0xa0/0x190
rxrpc_input_split_jumbo+0x198/0x1d0
rxrpc_input_data+0x14b/0x1e0
? rxrpc_input_call_packet+0xc2/0x1f0
rxrpc_input_call_event+0xad/0x6b0
rxrpc_input_packet_on_conn+0x1e1/0x210
rxrpc_input_packet+0x3f2/0x4d0
rxrpc_io_thread+0x243/0x410
? __pfx_rxrpc_io_thread+0x10/0x10
kthread+0xcf/0xe0
? __pfx_kthread+0x10/0x10
ret_from_fork+0x24/0x40
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Marc Dionne <marc.dionne@...istor.com>
cc: linux-afs@...ts.infradead.org
cc: linux-fsdevel@...r.kernel.org
---
fs/afs/internal.h | 2 +
fs/afs/rxrpc.c | 83 ++++++++++++++++++++++++++++++++++++++----------------
2 files changed, 61 insertions(+), 24 deletions(-)
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 6e1d3c4daf72..52aab09a32a9 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -130,6 +130,7 @@ struct afs_call {
wait_queue_head_t waitq; /* processes awaiting completion */
struct work_struct async_work; /* async I/O processor */
struct work_struct work; /* actual work processor */
+ struct work_struct free_work; /* Deferred free processor */
struct rxrpc_call *rxcall; /* RxRPC call handle */
struct rxrpc_peer *peer; /* Remote endpoint */
struct key *key; /* security for this call */
@@ -1331,6 +1332,7 @@ extern int __net_init afs_open_socket(struct afs_net *);
extern void __net_exit afs_close_socket(struct afs_net *);
extern void afs_charge_preallocation(struct work_struct *);
extern void afs_put_call(struct afs_call *);
+void afs_deferred_put_call(struct afs_call *call);
void afs_make_call(struct afs_call *call, gfp_t gfp);
void afs_wait_for_call_to_complete(struct afs_call *call);
extern struct afs_call *afs_alloc_flat_call(struct afs_net *,
diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index c453428f3c8b..9f2a3bb56ec6 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -18,6 +18,7 @@
struct workqueue_struct *afs_async_calls;
+static void afs_deferred_free_worker(struct work_struct *work);
static void afs_wake_up_call_waiter(struct sock *, struct rxrpc_call *, unsigned long);
static void afs_wake_up_async_call(struct sock *, struct rxrpc_call *, unsigned long);
static void afs_process_async_call(struct work_struct *);
@@ -149,6 +150,7 @@ static struct afs_call *afs_alloc_call(struct afs_net *net,
call->debug_id = atomic_inc_return(&rxrpc_debug_id);
refcount_set(&call->ref, 1);
INIT_WORK(&call->async_work, afs_process_async_call);
+ INIT_WORK(&call->free_work, afs_deferred_free_worker);
init_waitqueue_head(&call->waitq);
spin_lock_init(&call->state_lock);
call->iter = &call->def_iter;
@@ -159,6 +161,36 @@ static struct afs_call *afs_alloc_call(struct afs_net *net,
return call;
}
+static void afs_free_call(struct afs_call *call)
+{
+ struct afs_net *net = call->net;
+ int o;
+
+ ASSERT(!work_pending(&call->async_work));
+
+ rxrpc_kernel_put_peer(call->peer);
+
+ if (call->rxcall) {
+ rxrpc_kernel_shutdown_call(net->socket, call->rxcall);
+ rxrpc_kernel_put_call(net->socket, call->rxcall);
+ call->rxcall = NULL;
+ }
+ if (call->type->destructor)
+ call->type->destructor(call);
+
+ afs_unuse_server_notime(call->net, call->server, afs_server_trace_put_call);
+ kfree(call->request);
+
+ o = atomic_read(&net->nr_outstanding_calls);
+ trace_afs_call(call->debug_id, afs_call_trace_free, 0, o,
+ __builtin_return_address(0));
+ kfree(call);
+
+ o = atomic_dec_return(&net->nr_outstanding_calls);
+ if (o == 0)
+ wake_up_var(&net->nr_outstanding_calls);
+}
+
/*
* Dispose of a reference on a call.
*/
@@ -173,32 +205,34 @@ void afs_put_call(struct afs_call *call)
o = atomic_read(&net->nr_outstanding_calls);
trace_afs_call(debug_id, afs_call_trace_put, r - 1, o,
__builtin_return_address(0));
+ if (zero)
+ afs_free_call(call);
+}
- if (zero) {
- ASSERT(!work_pending(&call->async_work));
- ASSERT(call->type->name != NULL);
-
- rxrpc_kernel_put_peer(call->peer);
-
- if (call->rxcall) {
- rxrpc_kernel_shutdown_call(net->socket, call->rxcall);
- rxrpc_kernel_put_call(net->socket, call->rxcall);
- call->rxcall = NULL;
- }
- if (call->type->destructor)
- call->type->destructor(call);
+static void afs_deferred_free_worker(struct work_struct *work)
+{
+ struct afs_call *call = container_of(work, struct afs_call, free_work);
- afs_unuse_server_notime(call->net, call->server, afs_server_trace_put_call);
- kfree(call->request);
+ afs_free_call(call);
+}
- trace_afs_call(call->debug_id, afs_call_trace_free, 0, o,
- __builtin_return_address(0));
- kfree(call);
+/*
+ * Dispose of a reference on a call, deferring the cleanup to a workqueue
+ * to avoid lock recursion.
+ */
+void afs_deferred_put_call(struct afs_call *call)
+{
+ struct afs_net *net = call->net;
+ unsigned int debug_id = call->debug_id;
+ bool zero;
+ int r, o;
- o = atomic_dec_return(&net->nr_outstanding_calls);
- if (o == 0)
- wake_up_var(&net->nr_outstanding_calls);
- }
+ zero = __refcount_dec_and_test(&call->ref, &r);
+ o = atomic_read(&net->nr_outstanding_calls);
+ trace_afs_call(debug_id, afs_call_trace_put, r - 1, o,
+ __builtin_return_address(0));
+ if (zero)
+ schedule_work(&call->free_work);
}
static struct afs_call *afs_get_call(struct afs_call *call,
@@ -640,7 +674,8 @@ static void afs_wake_up_call_waiter(struct sock *sk, struct rxrpc_call *rxcall,
}
/*
- * wake up an asynchronous call
+ * Wake up an asynchronous call. The caller is holding the call notify
+ * spinlock around this, so we can't call afs_put_call().
*/
static void afs_wake_up_async_call(struct sock *sk, struct rxrpc_call *rxcall,
unsigned long call_user_ID)
@@ -657,7 +692,7 @@ static void afs_wake_up_async_call(struct sock *sk, struct rxrpc_call *rxcall,
__builtin_return_address(0));
if (!queue_work(afs_async_calls, &call->async_work))
- afs_put_call(call);
+ afs_deferred_put_call(call);
}
}
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