linux-kernel - Re: spinlock_irqsave() && flags (Was: pm80xx: Spinlock fix)

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Message-ID: <CA+55aFy_y45feJNJgFa=Taks0GpxiXEMJexhjVVYH-vVFkPmkA@mail.gmail.com>
Date:	Mon, 23 Dec 2013 10:12:57 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Jason Seba <jason.seba42@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Tomas Henzl <thenzl@...hat.com>, Jack Wang <xjtuwjp@...il.com>,
	Suresh Thiagarajan <Suresh.Thiagarajan@...s.com>,
	Viswas G <Viswas.G@...s.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"JBottomley@...allels.com" <JBottomley@...allels.com>,
	Vasanthalakshmi Tharmarajan 
	<Vasanthalakshmi.Tharmarajan@...s.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: spinlock_irqsave() && flags (Was: pm80xx: Spinlock fix)

On Mon, Dec 23, 2013 at 9:27 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> In short, is this code
>
>         spinlock_t LOCK;
>         unsigned long FLAGS;
>
>         void my_lock(void)
>         {
>                 spin_lock_irqsave(&LOCK, FLAGS);
>         }
>
>         void my_unlock(void)
>         {
>                 spin_unlock_irqrestore(&LOCK, FLAGS);
>         }
>
> correct or not?

Hell no. "flags" needs to be a thread-private variable, or at least
protected some way (ie the above could work if everything is inside a
bigger lock, to serialize access to FLAGS).

                    Linus
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