Re: deadlock avoidance?

Davide Libenzi (dlibenzi@maticad.it)
Wed, 8 Dec 1999 11:50:00 +0100

Wednesday, December 08, 1999 1:53 AM
Johannes Erdfelt <jerdfelt@sventech.com> wrote :
> > All pid and count modify fall inside 1) a nested lock ( ie. the task
> > already own the lock : ++lock->count )
> > 2) a lock acquired : lock->pid = getpid() and ++lock->count
>
> The setting is, but not all of the reading.
>

Hi Johannes,

There is not test & set operations other than spin_... in my code.
Look at it better and try to find a sequence of operations that stall it.

struct s_nested_lock {
spinlock_t lock;
short int pid;
short int count;
};

#define nested_lock(lock, flags) \
if (lock->pid == getpid()) { \
++lock->count; \
} else { \
spin_lock_irqsave(&lock->lock, flags); \
++lock->count; \
lock->pid = getpid(); \
}

#define nested_unlock(lock, flags) \
if (--lock->count == 0) { \
lock->pid = 0; \
spin_unlock_irqrestore(&lock->lock, flags); \
}

Cheers,
Davide.

--
"Debian, the Freedom in Freedom."






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