linux-kernel - Re: when spin_lock_irq (as opposed to spin_lock

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Message-Id: <200810111955.14667.arvidjaar@mail.ru>
Date:	Sat, 11 Oct 2008 19:55:13 +0400
From:	Andrey Borzenkov <arvidjaar@...l.ru>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: when spin_lock_irq (as opposed to spin_lock_irqsave) is appropriate?

On Saturday 11 October 2008, Oliver Neukum wrote:
> Am Samstag, 11. Oktober 2008 17:29:01 schrieb Andrey Borzenkov:
> > Logically, one piece of kernel code has no way to know whether another
> > piece of kernel code (or may be hard-/firmware) has disabled some
> > interrupt line. So it looks like spin_lock_irq should not even exist,
> > except may be for very specific cases (where we are sure no other piece
> > of kernel code may run concurrently)?
> > 
> > Sorry for stupid question, I an not actually a HW type of person ...
> > 
> 
> This has no connection with individual irq lines. It's about being able
> to sleep. Kernel code usually knows whether it can sleep.
> If it knows to be able to sleep it can use spin_lock_irq() which is
> more efficient than spin_lock_irqsave()
> 

Sorry? I can't sleep under spinlock ... *any* spinlock? Or has this changed?

May I be I was not clear with question. spin_lock_irq implies spin_unlock_irq,
which unconditionally enables interrupts. But I have no idea which interrupts
were disabled before spin_lock_irq; so I may accidentally enable too much?

Or what exactly "irq" in spin_(un-)lock_irq means?

TIA

-andrey

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