> The tasklist_lock is a rw spinlock. It is again a
> macro defined in <linux/spinlock.h>
I donot think it is a macro as I could see it in
fork.c
rwlock_t tasklist_lock __cacheline_aligned =
RW_LOCK_UNLOCKED;
This is a different thing from the error which I
encountered:
But getting following error:
unresolved symbol __read_lock_failed
I can see that tasklist_lock is exported. Pls see
below output
ksyms -a | grep tasklist
c0370a80 tasklist_lock_R999c80a2
c011f8e0 check_tasklist_locked_R15bb5893
The cause of problem is something else. On further
study, I found that read_lock invokes
__read_lock_failed if it fails in acquiring lock and
the __read_lock_failed is invoked which again tries to
achieve lock.
As __read_lock_failed is a function in assembly and
not exported, therefore it gives unresolved error.
For temporary fix, I defined this function in my
module
which is as below:
void __read_lock_failed(void)
{
printk("<1> LOCKING FAILED");
}
This change helped me to get rid of unresolved error.
But when I load this module, I could see that
__read_lock_failed has invoked.
//Code Snippet
read_lock(&tasklist_lock);
printk("<1> Iterating ");
for_each_process(p) {
printk ("<1> Iterating Task List " );
printk ("<1> Process PID=%i,
State=%i\n",p->pid,p->state);
}
Output of code :
LOCKING FAILED<1> Iterating <1> Iterating Task List
<1> Process PID=1, State=1
Iterating Task List <1> Process PID=2, State=1
Iterating Task List <1> Process PID=3, State=1
I am able to print the task list details successfully.
But could nopt able to understand why I failed in
obtaining lock.
Regards
Dinesh
--- Manish Regmi <regmi.manish@xxxxxxxxx> wrote:
> On 8/13/06, Dinesh Ahuja <mdlinux7@xxxxxxxxxxx>
> wrote:
> > Hi Manish,
> >
> > It is just a macro that expands to a for loop. It
> is
> > deffined in
> > sched.h
> >
> > #define for_each_process(p) \
> > for (p = &init_task ; (p = next_task(p)) !=
> > &init_task ; )
> >
> > Right this is a macro. On further investigation, I
> > found that init_task access init_task_union.task
> > {defined in include/asm-i386/processor.h} and
> > next_task is again a macro defined as
> > #define next_task(p)
> list_entry((p)->tasks.next,
> > struct task_struct, tasks)
> >
> > list_entry is again a macro defined in
> > {include/linux/list.h} as
> > #define list_entry(ptr, type, member) \
> > ((type *)((char *)(ptr)-(unsigned
> > long)(&((type *)0)->member)))
> >
> > In this case, macro uses a init_task_union which
> is
> > exported by kernel and that should be sufficient
> for
> > module to iterate over list. But if macro is using
> an
> > kernel symbol i.e function or a global variable,
> then
> > these symbols should be exported otherwise use of
> > macro will give unresolved symbols. Please verfiy
> my
> > understanding.
>
> correct.
>
> > I am trying to use read lock before iterating a
> task
> > list.
> >
> > read_lock(&tasklist_lock);
> > for_each_process(p) {
> > printk ("<1> Iterating
> Task
> > List" );
> > }
> > read_unlock(&tasklist_lock);
> >
> > But getting following error:
> > unresolved symbol __read_lock_failed
>
>
> The tasklist_lock is a rw spinlock. It is again a
> macro defined in
> <linux/spinlock.h>
>
> regards
> Manish Regmi
>
__________________________________________________________
Yahoo! India Answers: Share what you know. Learn something new
http://in.answers.yahoo.com/
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive: http://mail.nl.linux.org/kernelnewbies/
FAQ: http://kernelnewbies.org/faq/
