[PATCH] 2.5.4 Can't use spin_lock_* with wait_queue_head_t object.

[PATCH] 2.5.4 Can't use spin_lock_* with wait_queue_head_t object.

[Bob Miller]

There is code in sched.c that uses the spin_lock_* interfaces to acquire and
release the lock in the wait_queue_head_t embedded in the struct completion.

This is wrong and causes the system to OPPs on startup when compiled with
wait.h:USE_RW_WAIT_QUEUE_SPINLOCK set to 1.  The patch below changes the
spin_lock_* calls to wq_write_lock_*.


-- 
Bob Miller					Email: rem@osdl.org
Open Software Development Lab			Phone: 503.626.2455 Ext. 17



diff -ru linux.2.5.4-orig/include/linux/wait.h linux.2.5.4/include/linux/wait.h
--- linux.2.5.4-orig/include/linux/wait.h	Sun Feb 10 17:50:07 2002
+++ linux.2.5.4/include/linux/wait.h	Mon Feb 11 11:22:21 2002
@@ -45,6 +45,7 @@
 # define wq_read_unlock read_unlock
 # define wq_write_lock_irq write_lock_irq
 # define wq_write_lock_irqsave write_lock_irqsave
+# define wq_write_unlock_irq write_unlock_irq
 # define wq_write_unlock_irqrestore write_unlock_irqrestore
 # define wq_write_unlock write_unlock
 #else
@@ -57,6 +58,7 @@
 # define wq_read_unlock_irqrestore spin_unlock_irqrestore
 # define wq_write_lock_irq spin_lock_irq
 # define wq_write_lock_irqsave spin_lock_irqsave
+# define wq_write_unlock_irq spin_unlock_irq
 # define wq_write_unlock_irqrestore spin_unlock_irqrestore
 # define wq_write_unlock spin_unlock
 #endif
diff -ru linux.2.5.4-orig/kernel/sched.c linux.2.5.4/kernel/sched.c
--- linux.2.5.4-orig/kernel/sched.c	Sun Feb 10 17:50:12 2002
+++ linux.2.5.4/kernel/sched.c	Mon Feb 11 11:22:21 2002
@@ -806,15 +806,15 @@
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&x->wait.lock, flags);
+	wq_write_lock_irqsave(&x->wait.lock, flags);
 	x->done++;
 	__wake_up_common(&x->wait, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1, 0);
-	spin_unlock_irqrestore(&x->wait.lock, flags);
+	wq_write_unlock_irqrestore(&x->wait.lock, flags);
 }
 
 void wait_for_completion(struct completion *x)
 {
-	spin_lock_irq(&x->wait.lock);
+	wq_write_lock_irq(&x->wait.lock);
 	if (!x->done) {
 		DECLARE_WAITQUEUE(wait, current);
 
@@ -822,14 +822,14 @@
 		__add_wait_queue_tail(&x->wait, &wait);
 		do {
 			__set_current_state(TASK_UNINTERRUPTIBLE);
-			spin_unlock_irq(&x->wait.lock);
+			wq_write_unlock_irq(&x->wait.lock);
 			schedule();
-			spin_lock_irq(&x->wait.lock);
+			wq_write_lock_irq(&x->wait.lock);
 		} while (!x->done);
 		__remove_wait_queue(&x->wait, &wait);
 	}
 	x->done--;
-	spin_unlock_irq(&x->wait.lock);
+	wq_write_unlock_irq(&x->wait.lock);
 }
 
 #define	SLEEP_ON_VAR				\

Re: [PATCH] 2.5.4 Can't use spin_lock_* with wait_queue_head_t object.

[Richard B. Johnson]

On Tue, 12 Feb 2002, Bob Miller wrote:

> There is code in sched.c that uses the spin_lock_* interfaces to acquire and
> release the lock in the wait_queue_head_t embedded in the struct completion.
> 
Isn't it just that the spin_lock wasn't initialized at the start?


Cheers,
Dick Johnson

Penguin : Linux version 2.4.1 on an i686 machine (797.90 BogoMips).

    I was going to compile a list of innovations that could be
    attributed to Microsoft. Once I realized that Ctrl-Alt-Del
    was handled in the BIOS, I found that there aren't any.

Re: [PATCH] 2.5.4 Can't use spin_lock_* with wait_queue_head_t object.

[Bob Miller]

On Tue, Feb 12, 2002 at 04:23:39PM -0500, Richard B. Johnson wrote:

> On Tue, 12 Feb 2002, Bob Miller wrote:
> 
> > There is code in sched.c that uses the spin_lock_* interfaces to acquire and
> > release the lock in the wait_queue_head_t embedded in the struct completion.
> > 
> Isn't it just that the spin_lock wasn't initialized at the start?
> 

No.  The DECLARE_COMPLETION() macro was called in the case that oops'd.

The problem is that when wait.h:USE_RW_WAIT_QUEUE_SPINLOCK is set
the type of lock in the wait_queue_head_t changes from being a
spinlock_t to a rwlock_t.

If you also set CONFIG_DEBUG_SPINLOCK, the wq_lock_t in the
wait_queue_head_t is initialized with a rwlock_t magic number
(0xdeaf1eed), but the spin_lock_XXX() code checks for the spinlock_t
magic number (0xdead4ead) and calls BUG() when the check fails.


-- 
Bob Miller					Email: rem@osdl.org
Open Software Development Lab			Phone: 503.626.2455 Ext. 17