Re: uml-patch-2.5.42-1

Oleg Drokin
2002-10-15T11:55:07Z

Hello!

On Mon, Oct 14, 2002 at 07:58:28PM -0500, Jeff Dike wrote:
> UML has been updated to 2.5.42 and UML 2.4.19-12. In non-numeric terms,
> this means the following:
> the usual build fixes to keep up with kbuild
> the SMP work from UML 2.4.19-12 - it seems reasonably functional
> and stable, but there are some unexplained crashes still. Also, the fixes
> from UML 2.4.19-13 aren't in yet, so an SMP UML will leave children around
> after exiting (the idle threads for processors 1 ... ncpus - 1). These
> children will interfere with rebooting, and will also hold down host memory.
> various cleanups and bug fixes

Reviewing your patch I spotted some locking inconsistencies.
Also Nikita Danilov have spotted a double unlock in irq_user.c:reactivate_fd(),
you forgot to do return before "out" label.
Below is quotes from the patch, and at the very end of the message
there is a my proposed patch to fix all uncovered problems, patch was tested
as in "compiles and runs ok for me".

Also
arch/um/drivers/ubd_kern.c:
@@ -892,8 +948,11 @@

n = minor(rdev) >> UBD_SHIFT;
dev = &ubd_dev[n];
+
+ err = 0;
+ spin_lock(&ubd_lock);
if(dev->is_dir)
- return(0);
+ goto out;

err = ubd_file_size(dev, &size);
if (!err) {
@@ -902,7 +961,8 @@
set_capacity(fake_gendisk[n], size / 512);
dev->size = size;
}
-
+ spin_unlock(&ubd_lock);
+ out:
return err;
}

Here you forget to unlock ubd_lock if dev->is_dir is true.

arch/um/kernel/irq_user.c
+ /* Actually, it only looks like it can be called from interrupt
+ * context. The culprit is reactivate_fd, which calls
+ * maybe_sigio_broken, which calls write_sigio_workaround,
+ * which calls activate_fd. However, write_sigio_workaround should
+ * only be called once, at boot time. That would make it clear that
+ * this is called only from process context, and can be locked with
+ * a semaphore.
+ */
+ flags = irq_lock();
+ for(irq_fd = active_fds; irq_fd != NULL; irq_fd = irq_fd->next){
+ if((irq_fd->fd == fd) && (irq_fd->type == type)){
+ printk("Registering fd %d twice\n", fd);
+ printk("Irqs : %d, %d\n", irq_fd->irq, irq);
+ printk("Ids : 0x%x, 0x%x\n", irq_fd->id, dev_id);
+ goto out_free;
+ }
+ }
...
+ out_unlock:
+ irq_unlock(flags);
+ out_free:
kfree(new_fd);
+ out:
return(err);

Here you forgot to do irq_unlock()

Also there are number "32" is hardcoded into arch/um/kernel/trap_user.c
in some arrays, taht you probably actually want to make dependent on
CONFIG_NR_CPUS

Bye,
Oleg
===== arch/um/drivers/ubd_kern.c 1.9 vs edited =====
--- 1.9/arch/um/drivers/ubd_kern.c Tue Oct 15 10:44:19 2002
+++ edited/arch/um/drivers/ubd_kern.c Tue Oct 15 15:18:43 2002
@@ -961,8 +961,8 @@
set_capacity(fake_gendisk[n], size / 512);
dev->size = size;
}
- spin_unlock(&ubd_lock);
out:
+ spin_unlock(&ubd_lock);
return err;
}

===== arch/um/kernel/irq_user.c 1.3 vs edited =====
--- 1.3/arch/um/kernel/irq_user.c Tue Oct 15 10:44:20 2002
+++ edited/arch/um/kernel/irq_user.c Tue Oct 15 15:21:16 2002
@@ -157,7 +157,7 @@
printk("Registering fd %d twice\n", fd);
printk("Irqs : %d, %d\n", irq_fd->irq, irq);
printk("Ids : 0x%x, 0x%x\n", irq_fd->id, dev_id);
- goto out_free;
+ goto out_unlock;
}
}

@@ -209,7 +209,6 @@

out_unlock:
irq_unlock(flags);
- out_free:
kfree(new_fd);
out:
return(err);
@@ -344,6 +343,7 @@
* section.
*/
maybe_sigio_broken(fd, irq->type);
+ return;
out:
irq_unlock(flags);
}