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Date: Fri, 16 Mar 2007 18:05:05 +0200
From: Zilvinas Valinskas <zilvinas@...ibox.com>
To: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc: Ingo Molnar <mingo@...e.hu>
Subject: Re: LOCKDEP warning if CONFIG_DETECT_SOFTLOCKUP=y
Hello Ingo,
I think I've found a solution for a problem. Is this sane thing to do ?
At least lockdep is happy now, does not complain anymore. It seems that
->pi_lock was not register with lockdep correctly (something about
classes ... 8).
diff --git a/kernel/fork.c b/kernel/fork.c
index d154cc7..6af959c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -933,8 +933,8 @@ asmlinkage long sys_set_tid_address(int __user *tidptr)
static inline void rt_mutex_init_task(struct task_struct *p)
{
-#ifdef CONFIG_RT_MUTEXES
spin_lock_init(&p->pi_lock);
+#ifdef CONFIG_RT_MUTEXES
plist_head_init(&p->pi_waiters, &p->pi_lock);
p->pi_blocked_on = NULL;
#endif
On Fri, 2007-03-16 at 16:55 +0200, Zilvinas Valinskas wrote:
> Hello lkml,
>
> Booting ixp4xx/ARM/BE with lockdep enabled to test my code, I got a
> lockdep warning (see below). Does it mean that soft-lockup detector is
> started too early ? Any advice how to approach and fix the problem are
> appreciated very much. If CONFIG_DETECT_SOFTLOCKUP=n, lockdep does not
> complain.
>
> Kernel is vanilla 2.6.21-rc4 + lockdep-stacktrace.diff from
> http://svn.wantstofly.org/kernel/ repository.
>
>
> [ 0.000000] Linux version 2.6.21-rc4 (zilvinas@zv) (gcc version 4.2.0 20070207 (prerelease) (http://www.wilibox.com)) #12 Fri Mar 16 16:05:39 EET 2007
> [ 0.000000] CPU: XScale-IXP42x Family [690541f1] revision 1 (ARMv5TE), cr=000039ff
> [ 0.000000] Machine: Intel IXDP425 Development Platform
> [ 0.000000] Memory policy: ECC disabled, Data cache writeback
> ...
>
> [ 0.000000] Built 1 zonelists. Total pages: 16256
> [ 0.000000] Kernel command line: initcall_debug loglevel=8 i2c_debug=9 root=/dev/mtdblock2 console=ttyS0,115200 ro init=/linuxrc
> [ 0.000000] PID hash table entries: 256 (order: 8, 1024 bytes)
> [ 0.000000] Lock dependency validator: Copyright (c) 2006 Red Hat, Inc., Ingo Molnar
> [ 0.000000] ... MAX_LOCKDEP_SUBCLASSES: 8
> [ 0.000000] ... MAX_LOCK_DEPTH: 30
> [ 0.000000] ... MAX_LOCKDEP_KEYS: 2048
> [ 0.000000] ... CLASSHASH_SIZE: 1024
> [ 0.000000] ... MAX_LOCKDEP_ENTRIES: 8192
> [ 0.000000] ... MAX_LOCKDEP_CHAINS: 16384
> [ 0.000000] ... CHAINHASH_SIZE: 8192
> [ 0.000000] memory used by lock dependency info: 1096 kB
> [ 0.000000] per task-struct memory footprint: 1200 bytes
> [ 0.000000] ------------------------
> [ 0.000000] | Locking API testsuite:
>
> ... <skiped> ...
>
> [ 0.590000] -------------------------------------------------------
> [ 0.590000] Good, all 218 testcases passed! |
> [ 0.590000] ---------------------------------
> [ 0.590000] Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)
> [ 0.600000] Calibrating delay loop... 265.42 BogoMIPS (lpj=1327104)
> [ 0.840000] Mount-cache hash table entries: 512
> [ 0.840000] CPU: Testing write buffer coherency: ok
> [ 0.840000] INFO: trying to register non-static key.
> [ 0.840000] the code is fine but needs lockdep annotation.
> [ 0.840000] turning off the locking correctness validator.
>
> Don't know how to fix that.
>
> [ 0.840000] [<c0021018>] (dump_stack+0x0/0x14) from [<c0052ccc>] (__lock_acquire+0x640/0x1110)
> [ 0.840000] [<c005268c>] (__lock_acquire+0x0/0x1110) from [<c0053820>] (lock_acquire+0x84/0x98)
> [ 0.840000] [<c005379c>] (lock_acquire+0x0/0x98) from [<c01858b4>] (_spin_lock_irqsave+0x48/0x5c)
> [ 0.840000] [<c018586c>] (_spin_lock_irqsave+0x0/0x5c) from [<c002f358>] (sched_setscheduler+0xd4/0x2a8)
> [ 0.840000] r6 = C04D6000 r5 = C04D1820 r4 = 00000001
> [ 0.840000] [<c002f284>] (sched_setscheduler+0x0/0x2a8) from [<c0058848>] (watchdog+0x30/0x6c)
> [ 0.840000] [<c0058818>] (watchdog+0x0/0x6c) from [<c00494ec>] (kthread+0x108/0x118)
> [ 0.840000] r4 = 00000000
> [ 0.840000] [<c00493e4>] (kthread+0x0/0x118) from [<c0036098>] (do_exit+0x0/0x894)
> [ 0.840000] r7 = 00000000 r6 = 00000000 r5 = 00000000 r4 = 00000000
> [ 0.840000] Calling initcall 0xc0009980: ptrace_break_init+0x0/0x2c()
>
> With gdb it points to *__task_rq_lock(struct task_struct *p)
>
> (gdb) l *sched_setscheduler+0xd4
> 0x1644 is in sched_setscheduler (kernel/sched.c:395).
> 390 {
> 391 struct rq *rq;
> 392
> 393 repeat_lock_task:
> 394 rq = task_rq(p);
> 395 spin_lock(&rq->lock);
> 396 if (unlikely(rq != task_rq(p))) {
> 397 spin_unlock(&rq->lock);
> 398 goto repeat_lock_task;
> 399 }
> (gdb)
>
> I think it is really about ->pi_lock, on line 4134, that lockdep doesn't know
> anything about.
>
> 4130 /*
> 4131 * make sure no PI-waiters arrive (or leave) while we are
> 4132 * changing the priority of the task:
> 4133 */
> 4134 spin_lock_irqsave(&p->pi_lock, flags);
> 4135 /*
> 4136 * To be able to change p->policy safely, the apropriate
> 4137 * runqueue lock must be held.
> 4138 */
> 4139 rq = __task_rq_lock(p);
>
>
> Best regards,
> Žilvinas Valinskas
>
> -
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