[v2] afs: Fix lock recursion

Commit Message

David Howells Oct. 17, 2024, 10:58 a.m. UTC

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 <[e-mail]>
cc: Marc Dionne <[e-mail]>
cc: [e-mail]
cc: [e-mail]
---
 fs/afs/internal.h |    2 +
 fs/afs/rxrpc.c    |   83 ++++++++++++++++++++++++++++++++++++++----------------
 2 files changed, 61 insertions(+), 24 deletions(-)

Comments

Christian Brauner Oct. 17, 2024, 1:34 p.m. UTC | #1

On Thu, 17 Oct 2024 11:58:52 +0100, David Howells wrote:
> 
> 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.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] afs: Fix lock recursion
      https://git.kernel.org/vfs/vfs/c/610a79ffea02

Patch

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);
 	}
 }