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Message-Id: <1174056925.17967.15.camel@zv.wilibox.com>
Date: Fri, 16 Mar 2007 16:55:25 +0200
From: Zilvinas Valinskas <zilvinas@...ibox.com>
To: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc: Ingo Molnar <mingo@...e.hu>
Subject: LOCKDEP warning if CONFIG_DETECT_SOFTLOCKUP=y
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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