Re: cassini: possible recursive locking detected

[Emil Goode <emilgoode@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 3463 bytes --]

Hello Meelis,

I think this warning happens because we acquire multiple locks
in a loop in cas_lock_tx() and I believe we should use nested
lock annotation here.

Perhaps you would like to try the attached patch?

It won't fix the deadlock that you mentioned though.

Best regards,

Emil Goode

On Tue, May 06, 2014 at 12:39:48PM +0300, Meelis Roos wrote:
> While installing Linux on Sun Fire V480, any traffic on builtin cassini 
> NIC caused a hang. Worked this around by using Broadcom NIC and tried a 
> kernel with most debugging options. This resulted in the following 
> warning. Maybe this is the deadlonck I was seeing?
> 
> [   88.316595] =============================================
> [   88.316597] [ INFO: possible recursive locking detected ]
> [   88.316603] 3.15.0-rc4-00202-g30321c7-dirty #11 Not tainted
> [   88.316605] ---------------------------------------------
> [   88.316608] swapper/3/1 is trying to acquire lock:
> [   88.316644]  (&(&cp->tx_lock[i])->rlock){..-...}, at: [<0000000000745da0>] cas_link_timer+0xa0/0x460
> [   88.316646]
> [   88.316646] but task is already holding lock:
> [   88.316657]  (&(&cp->tx_lock[i])->rlock){..-...}, at: [<0000000000745da0>] cas_link_timer+0xa0/0x460
> [   88.316659]
> [   88.316659] other info that might help us debug this:
> [   88.316661]  Possible unsafe locking scenario:
> [   88.316661]
> [   88.316662]        CPU0
> [   88.316664]        ----
> [   88.316668]   lock(&(&cp->tx_lock[i])->rlock);
> [   88.316671]   lock(&(&cp->tx_lock[i])->rlock);
> [   88.316672]
> [   88.316672]  *** DEADLOCK ***
> [   88.316672]
> [   88.316674]  May be due to missing lock nesting notation
> [   88.316674]
> [   88.316677] 3 locks held by swapper/3/1:
> [   88.316694]  #0:  ((&cp->link_timer)){+.-...}, at: [<0000000000465f80>] call_timer_fn+0x0/0xe0
> [   88.316706]  #1:  (&(&cp->lock)->rlock){..-...}, at: [<0000000000745d80>] cas_link_timer+0x80/0x460
> [   88.316716]  #2:  (&(&cp->tx_lock[i])->rlock){..-...}, at: [<0000000000745da0>] cas_link_timer+0xa0/0x460
> [   88.316718]
> [   88.316718] stack backtrace:
> [   88.316724] CPU: 2 PID: 1 Comm: swapper/3 Not tainted 3.15.0-rc4-00202-g30321c7-dirty #11
> [   88.316727] Call Trace:
> [   88.316743]  [00000000004a2c5c] __lock_acquire+0x10fc/0x1fa0
> [   88.316749]  [00000000004a406c] lock_acquire+0x4c/0x80
> [   88.316760]  [000000000083e07c] _raw_spin_lock+0x1c/0x40
> [   88.316765]  [0000000000745da0] cas_link_timer+0xa0/0x460
> [   88.316769]  [0000000000465fc8] call_timer_fn+0x48/0xe0
> [   88.316775]  [00000000004665d4] run_timer_softirq+0x214/0x280
> [   88.316788]  [000000000045f650] __do_softirq+0xf0/0x240
> [   88.316800]  [000000000042bd0c] do_softirq_own_stack+0x2c/0x40
> [   88.316804]  [000000000045fb44] irq_exit+0xc4/0xe0
> [   88.316814]  [000000000042fcc8] timer_interrupt+0x88/0xc0
> [   88.316819]  [0000000000426b84] valid_addr_bitmap_patch+0xbc/0x238
> [   88.316826]  [00000000004ab2f8] vprintk_emit+0x1d8/0x540
> [   88.316842]  [0000000000835fb8] printk+0x34/0x48
> [   88.316847]  [00000000004ac3e0] register_console+0x340/0x3e0
> [   88.316862]  [0000000000a74f2c] init_netconsole+0x180/0x20c
> [   88.316867]  [0000000000426eb0] do_one_initcall+0x110/0x1a0
> 
> -- 
> Meelis Roos (mroos@linux.ee)
> --
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[-- Attachment #2: 0001-net-cassini-use-nested-lock-annotation.patch --]
[-- Type: text/x-diff, Size: 936 bytes --]

>From 1f3fcb0cb141e167c5389861eb0a6cb935f6a3d5 Mon Sep 17 00:00:00 2001
From: Emil Goode <emilgoode@gmail.com>
Date: Thu, 8 May 2014 12:49:24 +0200
Subject: [PATCH] net: cassini: use nested lock annotation

In the cas_lock_tx function we acquire multiple locks in a loop and
need to use nested lock annotation to prevent lockdep warnings.

Signed-off-by: Emil Goode <emilgoode@gmail.com>
---
 drivers/net/ethernet/sun/cassini.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/sun/cassini.c b/drivers/net/ethernet/sun/cassini.c
index df8d383..b9ac20f 100644
--- a/drivers/net/ethernet/sun/cassini.c
+++ b/drivers/net/ethernet/sun/cassini.c
@@ -246,7 +246,7 @@ static inline void cas_lock_tx(struct cas *cp)
 	int i;
 
 	for (i = 0; i < N_TX_RINGS; i++)
-		spin_lock(&cp->tx_lock[i]);
+		spin_lock_nested(&cp->tx_lock[i], i);
 }
 
 static inline void cas_lock_all(struct cas *cp)
-- 
1.7.10.4