[PATCH] Prevent deadlock in svc_defer

[Olaf Kirch <okir@suse.de>]

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Hi,

The svc_defer stuff introduced into svcsock.c recently is using spin_lock
rather than spin_lock_bh when grabbing sv_lock. This can cause deadlocks
as shown in this abridged stack dump:

0xc00000000fff76d0  0xc00000000020f8a0  .__spin_yield +0x44
0xc00000000fff76d0  0xc00000000020fa2c (lr) ._raw_spin_lock +0x58
0xc00000000fff7750  0xc00000000020fa2c  ._raw_spin_lock +0x58
0xc00000000fff77d0  0xc000000000374558  .svc_sock_enqueue +0x80
0xc00000000fff7860  0xc000000000375678  .svc_tcp_data_ready +0x5c
[...]
0xc00000000fff7b20  0xc000000000303c38  .ip_local_deliver +0xf4
[...]
0xc00000000fff7e50  0xc0000000002dba00  .net_rx_action +0x150
0xc00000000fff7f00  0xc000000000064638  .__do_softirq +0xa8
0xc00000000fff7f90  0xc000000000017530  .call_do_softirq +0x14
0xc0000003c0b17520  0xc000000000011f30  .do_softirq +0x90
0xc0000003c0b175b0  0xc000000000012ec8  .do_IRQ +0x10c
0xc0000003c0b17640  0xc00000000000b034  HardwareInterrupt_entry +0x14
--- Exception: 500: (Hardware Interrupt) at ._raw_spin_lock +0x28
0xc0000003c0b17930  0xc00000000020f9fc  ._raw_spin_lock +0x28
0xc0000003c0b17930  0xc00000000037591c (lr) .svc_revisit +0x64
0xc0000003c0b179b0  0xc00000000037591c  .svc_revisit +0x64
0xc0000003c0b17a60  0xc00000000037cb2c  .cache_revisit_request +0x18c
0xc0000003c0b17b00  0xc00000000037ea80  .cache_check +0x2b4
0xc0000003c0b17bc0  0xd0000000008d5ab0  .fh_verify +0x634

The attached patch should fix this problem.

Olaf
-- 
Olaf Kirch     |  The Hardware Gods hate me.
okir@suse.de   |
---------------+ 

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Index: linux-2.6.5/net/sunrpc/svcsock.c
===================================================================
--- linux-2.6.5.orig/net/sunrpc/svcsock.c	2004-08-04 08:58:54.000000000 +0200
+++ linux-2.6.5/net/sunrpc/svcsock.c	2004-08-04 09:04:12.000000000 +0200
@@ -1505,9 +1505,9 @@
 	dprintk("revisit queued\n");
 	svsk = dr->svsk;
 	dr->svsk = NULL;
-	spin_lock(&serv->sv_lock);
+	spin_lock_bh(&serv->sv_lock);
 	list_add(&dr->handle.recent, &svsk->sk_deferred);
-	spin_unlock(&serv->sv_lock);
+	spin_unlock_bh(&serv->sv_lock);
 	set_bit(SK_DEFERRED, &svsk->sk_flags);
 	svc_sock_enqueue(svsk);
 	svc_sock_put(svsk);
@@ -1538,10 +1538,10 @@
 		dr->argslen = rqstp->rq_arg.len >> 2;
 		memcpy(dr->args, rqstp->rq_arg.head[0].iov_base-skip, dr->argslen<<2);
 	}
-	spin_lock(&rqstp->rq_server->sv_lock);
+	spin_lock_bh(&rqstp->rq_server->sv_lock);
 	rqstp->rq_sock->sk_inuse++;
 	dr->svsk = rqstp->rq_sock;
-	spin_unlock(&rqstp->rq_server->sv_lock);
+	spin_unlock_bh(&rqstp->rq_server->sv_lock);
 
 	dr->handle.revisit = svc_revisit;
 	return &dr->handle;
@@ -1571,7 +1571,7 @@
 	
 	if (!test_bit(SK_DEFERRED, &svsk->sk_flags))
 		return NULL;
-	spin_lock(&serv->sv_lock);
+	spin_lock_bh(&serv->sv_lock);
 	clear_bit(SK_DEFERRED, &svsk->sk_flags);
 	if (!list_empty(&svsk->sk_deferred)) {
 		dr = list_entry(svsk->sk_deferred.next,
@@ -1580,6 +1580,6 @@
 		list_del_init(&dr->handle.recent);
 		set_bit(SK_DEFERRED, &svsk->sk_flags);
 	}
-	spin_unlock(&serv->sv_lock);
+	spin_unlock_bh(&serv->sv_lock);
 	return dr;
 }