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authorDavid Howells <dhowells@redhat.com>2016-08-03 14:11:40 +0100
committerDavid S. Miller <davem@davemloft.net>2016-08-06 00:08:40 -0400
commit372ee16386bbf6dc5eeb0387e1ede963debba82a (patch)
tree4c5cd4fa95199f9a3fe4a8bcd172a1eb11a3a52c /net/rxrpc/skbuff.c
parent54447f1ad73414ebb052e9a33d079cabed3a03e8 (diff)
downloadlinux-372ee16386bbf6dc5eeb0387e1ede963debba82a.tar.bz2
rxrpc: Fix races between skb free, ACK generation and replying
Inside the kafs filesystem it is possible to occasionally have a call processed and terminated before we've had a chance to check whether we need to clean up the rx queue for that call because afs_send_simple_reply() ends the call when it is done, but this is done in a workqueue item that might happen to run to completion before afs_deliver_to_call() completes. Further, it is possible for rxrpc_kernel_send_data() to be called to send a reply before the last request-phase data skb is released. The rxrpc skb destructor is where the ACK processing is done and the call state is advanced upon release of the last skb. ACK generation is also deferred to a work item because it's possible that the skb destructor is not called in a context where kernel_sendmsg() can be invoked. To this end, the following changes are made: (1) kernel_rxrpc_data_consumed() is added. This should be called whenever an skb is emptied so as to crank the ACK and call states. This does not release the skb, however. kernel_rxrpc_free_skb() must now be called to achieve that. These together replace rxrpc_kernel_data_delivered(). (2) kernel_rxrpc_data_consumed() is wrapped by afs_data_consumed(). This makes afs_deliver_to_call() easier to work as the skb can simply be discarded unconditionally here without trying to work out what the return value of the ->deliver() function means. The ->deliver() functions can, via afs_data_complete(), afs_transfer_reply() and afs_extract_data() mark that an skb has been consumed (thereby cranking the state) without the need to conditionally free the skb to make sure the state is correct on an incoming call for when the call processor tries to send the reply. (3) rxrpc_recvmsg() now has to call kernel_rxrpc_data_consumed() when it has finished with a packet and MSG_PEEK isn't set. (4) rxrpc_packet_destructor() no longer calls rxrpc_hard_ACK_data(). Because of this, we no longer need to clear the destructor and put the call before we free the skb in cases where we don't want the ACK/call state to be cranked. (5) The ->deliver() call-type callbacks are made to return -EAGAIN rather than 0 if they expect more data (afs_extract_data() returns -EAGAIN to the delivery function already), and the caller is now responsible for producing an abort if that was the last packet. (6) There are many bits of unmarshalling code where: ret = afs_extract_data(call, skb, last, ...); switch (ret) { case 0: break; case -EAGAIN: return 0; default: return ret; } is to be found. As -EAGAIN can now be passed back to the caller, we now just return if ret < 0: ret = afs_extract_data(call, skb, last, ...); if (ret < 0) return ret; (7) Checks for trailing data and empty final data packets has been consolidated as afs_data_complete(). So: if (skb->len > 0) return -EBADMSG; if (!last) return 0; becomes: ret = afs_data_complete(call, skb, last); if (ret < 0) return ret; (8) afs_transfer_reply() now checks the amount of data it has against the amount of data desired and the amount of data in the skb and returns an error to induce an abort if we don't get exactly what we want. Without these changes, the following oops can occasionally be observed, particularly if some printks are inserted into the delivery path: general protection fault: 0000 [#1] SMP Modules linked in: kafs(E) af_rxrpc(E) [last unloaded: af_rxrpc] CPU: 0 PID: 1305 Comm: kworker/u8:3 Tainted: G E 4.7.0-fsdevel+ #1303 Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014 Workqueue: kafsd afs_async_workfn [kafs] task: ffff88040be041c0 ti: ffff88040c070000 task.ti: ffff88040c070000 RIP: 0010:[<ffffffff8108fd3c>] [<ffffffff8108fd3c>] __lock_acquire+0xcf/0x15a1 RSP: 0018:ffff88040c073bc0 EFLAGS: 00010002 RAX: 6b6b6b6b6b6b6b6b RBX: 0000000000000000 RCX: ffff88040d29a710 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88040d29a710 RBP: ffff88040c073c70 R08: 0000000000000001 R09: 0000000000000001 R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: ffff88040be041c0 R15: ffffffff814c928f FS: 0000000000000000(0000) GS:ffff88041fa00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa4595f4750 CR3: 0000000001c14000 CR4: 00000000001406f0 Stack: 0000000000000006 000000000be04930 0000000000000000 ffff880400000000 ffff880400000000 ffffffff8108f847 ffff88040be041c0 ffffffff81050446 ffff8803fc08a920 ffff8803fc08a958 ffff88040be041c0 ffff88040c073c38 Call Trace: [<ffffffff8108f847>] ? mark_held_locks+0x5e/0x74 [<ffffffff81050446>] ? __local_bh_enable_ip+0x9b/0xa1 [<ffffffff8108f9ca>] ? trace_hardirqs_on_caller+0x16d/0x189 [<ffffffff810915f4>] lock_acquire+0x122/0x1b6 [<ffffffff810915f4>] ? lock_acquire+0x122/0x1b6 [<ffffffff814c928f>] ? skb_dequeue+0x18/0x61 [<ffffffff81609dbf>] _raw_spin_lock_irqsave+0x35/0x49 [<ffffffff814c928f>] ? skb_dequeue+0x18/0x61 [<ffffffff814c928f>] skb_dequeue+0x18/0x61 [<ffffffffa009aa92>] afs_deliver_to_call+0x344/0x39d [kafs] [<ffffffffa009ab37>] afs_process_async_call+0x4c/0xd5 [kafs] [<ffffffffa0099e9c>] afs_async_workfn+0xe/0x10 [kafs] [<ffffffff81063a3a>] process_one_work+0x29d/0x57c [<ffffffff81064ac2>] worker_thread+0x24a/0x385 [<ffffffff81064878>] ? rescuer_thread+0x2d0/0x2d0 [<ffffffff810696f5>] kthread+0xf3/0xfb [<ffffffff8160a6ff>] ret_from_fork+0x1f/0x40 [<ffffffff81069602>] ? kthread_create_on_node+0x1cf/0x1cf Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/rxrpc/skbuff.c')
-rw-r--r--net/rxrpc/skbuff.c41
1 files changed, 34 insertions, 7 deletions
diff --git a/net/rxrpc/skbuff.c b/net/rxrpc/skbuff.c
index eee0cfd9ac8c..06c51d4b622d 100644
--- a/net/rxrpc/skbuff.c
+++ b/net/rxrpc/skbuff.c
@@ -98,11 +98,39 @@ static void rxrpc_hard_ACK_data(struct rxrpc_call *call,
spin_unlock_bh(&call->lock);
}
+/**
+ * rxrpc_kernel_data_consumed - Record consumption of data message
+ * @call: The call to which the message pertains.
+ * @skb: Message holding data
+ *
+ * Record the consumption of a data message and generate an ACK if appropriate.
+ * The call state is shifted if this was the final packet. The caller must be
+ * in process context with no spinlocks held.
+ *
+ * TODO: Actually generate the ACK here rather than punting this to the
+ * workqueue.
+ */
+void rxrpc_kernel_data_consumed(struct rxrpc_call *call, struct sk_buff *skb)
+{
+ struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+
+ _enter("%d,%p{%u}", call->debug_id, skb, sp->hdr.seq);
+
+ ASSERTCMP(sp->call, ==, call);
+ ASSERTCMP(sp->hdr.type, ==, RXRPC_PACKET_TYPE_DATA);
+
+ /* TODO: Fix the sequence number tracking */
+ ASSERTCMP(sp->hdr.seq, >=, call->rx_data_recv);
+ ASSERTCMP(sp->hdr.seq, <=, call->rx_data_recv + 1);
+ ASSERTCMP(sp->hdr.seq, >, call->rx_data_eaten);
+
+ call->rx_data_recv = sp->hdr.seq;
+ rxrpc_hard_ACK_data(call, sp);
+}
+EXPORT_SYMBOL(rxrpc_kernel_data_consumed);
+
/*
- * destroy a packet that has an RxRPC control buffer
- * - advance the hard-ACK state of the parent call (done here in case something
- * in the kernel bypasses recvmsg() and steals the packet directly off of the
- * socket receive queue)
+ * Destroy a packet that has an RxRPC control buffer
*/
void rxrpc_packet_destructor(struct sk_buff *skb)
{
@@ -112,9 +140,8 @@ void rxrpc_packet_destructor(struct sk_buff *skb)
_enter("%p{%p}", skb, call);
if (call) {
- /* send the final ACK on a client call */
- if (sp->hdr.type == RXRPC_PACKET_TYPE_DATA)
- rxrpc_hard_ACK_data(call, sp);
+ if (atomic_dec_return(&call->skb_count) < 0)
+ BUG();
rxrpc_put_call(call);
sp->call = NULL;
}