From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
"Eric Dumazet" <edumazet@google.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
"Alexandre FOURNIER" <alexandre.fournier@wisp-e.com>,
"Ezequiel Garcia" <ezequiel.garcia@free-electrons.com>,
"Marcin Wojtas" <mw@semihalf.com>,
"Gregory Clément" <gregory.clement@free-electrons.com>
Subject: Re: RCU stall in af_unix.c, should use spin_lock_irqsave?
Date: Tue, 21 Oct 2014 12:10:11 +0200 [thread overview]
Message-ID: <20141021121011.53686d5f@free-electrons.com> (raw)
In-Reply-To: <1413885874.23173.11.camel@edumazet-glaptop2.roam.corp.google.com>
Dear Eric Dumazet,
On Tue, 21 Oct 2014 03:04:34 -0700, Eric Dumazet wrote:
> > So, the question is: is this patch the correct solution (but then other
> > usage of spin_lock in af_unix.c might also need fixing) ? Or is the
> > network driver at fault?
> >
> > Thanks for your input,
> >
> > Thomas
>
> Locks in af_unix do not need to mask irqs. Ever.
>
> skb_queue_tail() uses an irqsave variant because its a generic function,
> and _some_ skb list might be manipulated from hard irq handlers in pre
> NAPI drivers. But af_unix does not have an interrupt handler that could
> potentially try to lock sk_receive_queue.lock
Ok. So it's actually safe to mix spin_lock() and spin_lock_irqsave() on
the same lock, if you know that this lock will never ever be taken in
an interrupt context?
> mvpp2 is seriously brain damaged : on_each_cpu() cannot be used from
> a bottom half handler.
That's what I thought. Back to the drawing board then, to fix mvpp2.
Do you think there is a place where we can write down those
assumptions? It isn't easy to spot whether on_each_cpu() is safe to use
in a bottom half or not.
Anyway, thanks a lot for your quick feedback!
Best regards,
Thomas
--
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
next prev parent reply other threads:[~2014-10-21 10:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-21 8:03 RCU stall in af_unix.c, should use spin_lock_irqsave? Thomas Petazzoni
2014-10-21 10:04 ` Eric Dumazet
2014-10-21 10:10 ` Thomas Petazzoni [this message]
2014-10-21 10:28 ` Eric Dumazet
2014-10-21 11:58 ` Thomas Petazzoni
2014-10-21 10:08 ` Hannes Frederic Sowa
2014-10-21 10:13 ` Thomas Petazzoni
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