From: Uladzislau Rezki <urezki@gmail.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Joel Fernandes <joel@joelfernandes.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
Ext4 Developers List <linux-ext4@vger.kernel.org>,
Suraj Jitindar Singh <surajjs@amazon.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC] ext4: fix potential race between online resizing and write operations
Date: Sun, 1 Mar 2020 13:07:02 +0100 [thread overview]
Message-ID: <20200301120702.GA9762@pc636> (raw)
In-Reply-To: <20200301110843.GA8725@pc636>
> > > So in CONFIG_PREEMPT kernel we can identify if we are in atomic or not by
> > > using rcu_preempt_depth() and in_atomic(). When it comes to !CONFIG_PREEMPT
> > > then we skip it and consider as atomic. Something like:
> > >
> > > <snip>
> > > static bool is_current_in_atomic()
> >
> > Would be good to change this to is_current_in_rcu_reader() since
> > rcu_preempt_depth() does not imply atomicity.
> >
> can_current_synchronize_rcu()? If can we just call:
>
> <snip>
> synchronize_rcu() or synchronize_rcu_expedited();
> kvfree();
> <snip>
>
> > > {
> > > #ifdef CONFIG_PREEMPT_RCU
> > > if (!rcu_preempt_depth() && !in_atomic())
> > > return false;
> >
> > I think use if (!rcu_preempt_depth() && preemptible()) here.
> >
> > preemptible() checks for IRQ disabled section as well.
> >
> Yes but in_atomic() does it as well, it also checks other atomic
> contexts like softirq handlers and NMI ones. So calling there
> synchronize_rcu() is not allowed.
>
Ahh. Right you are. We also have to check if irqs are disabled
or not. preemptible() has to be added as well.
<snip>
can_current_synchronize_rcu()
{
if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
if (!rcu_preempt_depth() && !in_atomic() && preemptible()) {
might_sleep();
return true;
}
}
return false;
}
<snip>
if we can synchronize:
- we can directly inline kvfree() to current context;
- we can attached the head using GFP_KERNEL | __GFP_RETRY_MAYFAIL.
Otherwise attached the rcu_head under atomic or as we are in RCU reader section.
Thoughts?
--
Vlad Rezki
next prev parent reply other threads:[~2020-03-01 12:07 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200215233817.GA670792@mit.edu>
[not found] ` <20200216121246.GG2935@paulmck-ThinkPad-P72>
[not found] ` <20200217160827.GA5685@pc636>
[not found] ` <20200217193314.GA12604@mit.edu>
2020-02-18 17:08 ` [PATCH RFC] ext4: fix potential race between online resizing and write operations Uladzislau Rezki
2020-02-20 4:52 ` Theodore Y. Ts'o
2020-02-21 0:30 ` Paul E. McKenney
2020-02-21 13:14 ` Uladzislau Rezki
2020-02-21 20:22 ` Paul E. McKenney
2020-02-22 22:24 ` Joel Fernandes
2020-02-23 1:10 ` Paul E. McKenney
2020-02-24 17:40 ` Uladzislau Rezki
2020-02-25 2:07 ` Joel Fernandes
2020-02-25 3:55 ` Paul E. McKenney
2020-02-25 14:17 ` Joel Fernandes
2020-02-25 16:38 ` Paul E. McKenney
2020-02-25 17:00 ` Joel Fernandes
2020-02-25 18:54 ` Uladzislau Rezki
2020-02-25 22:47 ` Paul E. McKenney
2020-02-26 13:04 ` Uladzislau Rezki
2020-02-26 15:06 ` Paul E. McKenney
2020-02-26 15:53 ` Uladzislau Rezki
2020-02-27 14:08 ` Joel Fernandes
2020-03-01 11:13 ` Uladzislau Rezki
2020-02-27 13:37 ` Joel Fernandes
2020-03-01 11:08 ` Uladzislau Rezki
2020-03-01 12:07 ` Uladzislau Rezki [this message]
2020-02-25 2:11 ` Joel Fernandes
2020-02-21 12:06 ` Joel Fernandes
2020-02-21 13:28 ` Joel Fernandes
2020-02-21 19:21 ` Uladzislau Rezki
2020-02-21 19:25 ` Uladzislau Rezki
2020-02-22 22:12 ` Joel Fernandes
2020-02-24 17:02 ` Uladzislau Rezki
2020-02-24 23:14 ` Paul E. McKenney
2020-02-25 1:48 ` Joel Fernandes
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