linux-kernel - BUG: spinlock lockup

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Date:	Sat, 18 Jan 2014 12:55:51 +0530
From:	naveen yadav <yad.naveen@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org, will.deacon@....com
Subject: BUG: spinlock lockup

Dear All,

We are using 3.8.x  kernel on ARM, We are facing soft lockup issue.
Following are the logs.

BUG: spinlock lockup suspected on CPU#0, process1/525
lock: 0xd8ac9a64, .magic: dead4ead, .owner: <none>/-1, .owner_cpu: -1

1 . Looks like lock is available as owner is -1, why arch_spin_trylock
is getting failed ?

2. There is a patch : ARM: spinlock: retry trylock operation if strex
fails on free lock
http://permalink.gmane.org/gmane.linux.ports.arm.kernel/240913
In this patch, A loop has been added around strexeq %2, %0, [%3]".
{Comment "retry the trylock operation if the lock appears
to be free but the strex reported failure"}

but arch_spin_trylock is called by __spin_lock_debug and its already
getting called in loops. So what purpose is resolves?

static void __spin_lock_debug(raw_spinlock_t *lock)
{
        u64 i;
        u64 loops = loops_per_jiffy * HZ;

        for (i = 0; i < loops; i++) {
                if (arch_spin_trylock(&lock->raw_lock))
                        return;
                __delay(1);
        }
        /* lockup suspected: */
        spin_dump(lock, "lockup suspected");
}

3. Is this patch useful to us, How can we reproduce this scenario ?
Scenario : Lock is available but arch_spin_trylock  is returning as failure

Thanks
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