linux-kernel - Re: [PATCH] fs/proc: Move kfree outside pde_unload

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Message-ID: <CACVxJT_ZRvznb3M=jq_du_aJvRmjcAb3=LSXFGYFWe5W2xo93A@mail.gmail.com>
Date:	Wed, 29 Aug 2012 16:50:50 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Nathan Zimmer <nzimmer@....com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] fs/proc: Move kfree outside pde_unload_lock

On Wed, Aug 29, 2012 at 7:11 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> I'll polish this patch once LKS/LPC is over...

It should oops in the following way (excuse Gmail please):
PDEO is removed from lists
->pde_users is 0
PDE won't be in purge queue -- no ->release while module is alive

Current code removes PDEO and checks if PDE scheduled for removal atomically.

proc_reg_release                                        remove_proc_entry

                                                        de->proc_fops = NULL;
release = pde_opener_del(inode, file);
rcu_read_lock();
                                                        synchronize_rcu();
fops = rcu_dereference(pde->proc_fops);
if (!fops) {
        rcu_read_unlock();
                         ----------------------------------
                                                        /* NOP */
                                                        while
(atomic_read(&de->pde_users))
                                                                ...
                                                        /* NOP */

pde_openers_purge(de, &purge_queue);
                                                        /* NOP */
                                                        while
(!list_empty(&purge_queue))
                                                                ...
                                                        rmmod

        if (release)
                release(inode, file) /* OOPS */
--
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