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Subject: Re: 2.6.14 kernels and above copy_to_user stupidity with IRQ disabled check
Date: Fri, 27 Jan 2006 15:18:06 -0500
Message-ID: <Pine.LNX.4.61.0601271513360.15124@chaos.analogic.com>
Thread-Topic: 2.6.14 kernels and above copy_to_user stupidity with IRQ disabled check
Thread-Index: AcYjfsjXFEVsIqxES5SquOHiikVbRg==
References: <43DA62CC.8090309@wolfmountaingroup.com>
From: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
To: "Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>
Cc: "linux-kernel" <linux-kernel@vger.kernel.org>
Reply-To: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Fri, 27 Jan 2006, Jeff V. Merkey wrote:

>
> Is there a good reason someone set a disabled_irq() check on 2.6.14 and
> above for copy_to_user to barf out
> tons of bogus stack dump messages if the function is called from within
> a spinlock:
>

This is a joke, right????

> i.e.
>
> spin_lock_irqsave(&regen_lock, regen_flags);
>    v = regen_head;
>    while (v)
>    {
>       if (i >= count)
>          return -EFAULT;

** BUG **  return with spin-lock held!

>
>
>       err = copy_to_user(&s[i++], v, sizeof(VIRTUAL_SETUP));

** BUG ** copy to user with spinlock held!

>       if (err)
>          return err;
>

** BUG ** Return with spin-lock held!
>
>       v = v->next;
>    }
>    spin_unlock_irqrestore(&regen_lock, regen_flags);
>
> is now busted and worked in kernels up to this point.  The error message
> is annoying but non-fatal.
>
> Jeff

It was NEVER supposed to work! The only reason it worked is because
your page(s) copied to, were not swapped out. If they were swapped
out, you are stuck, the page-fault won't occur.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.13.4 on an i686 machine (5589.66 BogoMips).
Warning : 98.36% of all statistics are fiction.
.

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