linux-kernel - Re: RCU stall in af_unix.c, should use spin_lock

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Message-ID: <1413887300.23173.14.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 21 Oct 2014 03:28:20 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Alexandre FOURNIER <alexandre.fournier@...p-e.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Marcin Wojtas <mw@...ihalf.com>,
	Gregory Clément 
	<gregory.clement@...e-electrons.com>
Subject: Re: RCU stall in af_unix.c, should use spin_lock_irqsave?

On Tue, 2014-10-21 at 12:10 +0200, Thomas Petazzoni wrote:

> 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?

Sure.

> 
> > 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.
> 

Really ? kernel/smp.c is full of comments.

Too many comments and people seem to not read them ;)

Take a look at smp_call_function(), which is called from on_each_cpu()


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