Re: [PATCH 0/4] Was: deferring __fput()

From: Al Viro
Date: Sun Jul 01 2012 - 16:57:26 EST

On Sun, Jul 01, 2012 at 03:50:02PM -0400, Mimi Zohar wrote:
> I haven't mentioned the "ima: defer calling __fput()" patch, since I've
> compiled git://
> #untested with a .config based on config-3.4.2-1.fc16.x86_64 and am
> having this problem. No need to add more confusion. The "ima: defer
> calling __fput()" will be dropped from the patchset, as soon as the
> general method works.
> I've isolated the problem to the PF_KTHREAD section of fput().
> void fput(struct file *file)
> {
> if (atomic_long_dec_and_test(&file->f_count)) {
> struct task_struct *task = current;
> file_sb_list_del(file);
> if (unlikely(in_interrupt() || task->flags & PF_KTHREAD)) {
> unsigned long flags;
> spin_lock_irqsave(&delayed_fput_lock, flags);
> list_add(&file->f_u.fu_list, &delayed_fput_list);
> schedule_work(&delayed_fput_work);
> spin_unlock_irqrestore(&delayed_fput_lock, flags);
> return;
> }
> init_task_work(&file->f_u.fu_rcuhead, ____fput);
> task_work_add(task, &file->f_u.fu_rcuhead, true);
> }
> }
> Replacing it with a call to __fput(), the system boots.

"it" being just the part under that if (unlikely(...)))? Very interesting... If so, we
have some kernel thread ending up with delayed __fput() which somehow makes dracut (assuimg
you are using fedora initramfs to go with fedora config) unhappy. With your own patch,
doing async __fput() in a lot of cases when this one doesn't delay past the return to
userland managing to survive the boot... I wonder which files end up triggering that fun
and which kernel thread is responsible... Could you slap a printk() in there, showing
file->f_dentry->d_inode->i_mode (octal) and at least file->f_dentry->
Along with the current->comm[], all under that inner if (). And see which ones end up
going that way by the time execve() of /sbin/init fails.

It would be nice to see which sys_mount() calls are made and which (if any) fail, BTW.
I wonder if it even gets to mounting the right root...
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