From mboxrd@z Thu Jan  1 00:00:00 1970
From: premdas.prajosh@gmail.com (Prajosh Premdas)
Date: Wed, 2 Nov 2011 19:23:25 +0530
Subject: spin_lock behavior
Message-ID: <CAAFf3B9v-XSySh5nB6XLN1c_AWdeHhDfaybz_hDopasmfy6TgA@mail.gmail.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

Hi

I wrote a sample module which looked like this and i expected the module to
hang as i have used 2 spin_lock simultaneously. But i find the print after
the second spin_lock being printed and the module works perfectly fine. Can
any body please help me in understanding this? I got this problem from a
driver i wrote and had a typo "spin_lock" instead of "spin_unlock" the
driver worked fine and i caught the mistake only during a review

*#include <linux/module.h>*
*#include <linux/spinlock.h>*
*
*
*struct sp_q {*
*spinlock_t spinlock;*
*uint8_t data;*
*};*
*
*
*static int __init sp_lck_init(void)*
*{*
*
*
*   struct sp_q test;*
*   *
*   /* Spin lock Init */*
*
*
*   spin_lock_init(&test.spinlock);*
*    *
*   printk("<1>Test start\n");*
*   *
*   spin_lock(&test.spinlock);*
*   test.data = 0;   *
*   spin_lock(&test.spinlock);   *
*   *
*   printk("<1>How come???\n");*
*   return 0;*
*
*
*}*
*
*
*static void __exit sp_lck_exit(void)*
*{*
*
*
*}*
*
*
*module_init(sp_lck_init);*
*module_exit(sp_lck_exit);*
*MODULE_LICENSE("GPL");*

-- 
Regards,

Prajosh Premdas
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