linux-kernel - Re: [RFC patch] vsprintf: Add %pav extension for print_vma

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Message-Id: <20150527141908.4cf02ef4456201ad7db78883@linux-foundation.org>
Date:	Wed, 27 May 2015 14:19:08 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joe Perches <joe@...ches.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC patch] vsprintf: Add %pav extension for print_vma_addr

On Wed, 27 May 2015 14:09:31 -0700 Joe Perches <joe@...ches.com> wrote:

> > Problems when CONFIG_PREEMPT=n.
> > 
> > > +	down_read(&mm->mmap_sem);
> > > +	vma = find_vma(mm, ip);
> > > +	if (vma && vma->vm_file) {
> > > +		struct file *f = vma->vm_file;
> > > +		char *gfp_buf = (char *)__get_free_page(GFP_KERNEL);
> > 
> > We shouldn't assume we can use GFP_KERNEL here.  Even if the
> > preempt_count() worked, we might be in a context which requires
> > GFP_NOFS or GFP_NOIO.
> 
> This code is basically a copy of the existing print_vma_addr()
> so is that true for all the existing uses too?

Yeah, the current code is pretty junky.  But normally print_vma_addr()
should never be called so nobody noticed...

In e8bff74a Ingo did a fiddle to preempt_conditional_sti() which looks
like it will address the CONFIG_PREEMPT=n issue, but only on x86.
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