int ptrace_attach(struct task_struct *task)
{
int retval;
retval = -EPERM;
if (task->pid <= 1)
goto out;
if (task->tgid == current->tgid)
goto out;
repeat:
/*
* Nasty, nasty.
*
* We want to hold both the task-lock and the
* tasklist_lock for writing at the same time.
* But that's against the rules (tasklist_lock
* is taken for reading by interrupts on other
* cpu's that may have task_lock).
*/
task_lock(task);
local_irq_disable();
if (!write_trylock(&tasklist_lock)) {
local_irq_enable();
task_unlock(task);
do {
cpu_relax();
} while (!write_can_lock(&tasklist_lock));
goto repeat;
}
/* the same process cannot be attached many times */
if (task->ptrace & PT_PTRACED)
goto bad;
retval = may_attach(task);
if (retval)
goto bad;
/* Go */
task->ptrace |= PT_PTRACED | ((task->real_parent != current)
? PT_ATTACHED : 0);
if (capable(CAP_SYS_PTRACE))
task->ptrace |= PT_PTRACE_CAP;
__ptrace_link(task, current);
force_sig_specific(SIGSTOP, task);
bad:
write_unlock_irq(&tasklist_lock);
task_unlock(task);
out:
return retval;
}
/*
* returns 1 if we get the read lock and 0 if we don't
* this won't wait for blocking writers or readers
*/
int btrfs_try_tree_write_lock(struct extent_buffer *eb)
{
if (atomic_read(&eb->blocking_writers) ||
atomic_read(&eb->blocking_readers))
return 0;
if (!write_trylock(&eb->lock))
return 0;
if (atomic_read(&eb->blocking_writers) ||
atomic_read(&eb->blocking_readers)) {
write_unlock(&eb->lock);
return 0;
}
atomic_inc(&eb->write_locks);
atomic_inc(&eb->spinning_writers);
eb->lock_owner = current->pid;
return 1;
}
