linux-kernel - Re: [PATCH] dax, pmem: add support for msync

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Date:	Wed, 2 Sep 2015 12:47:39 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Boaz Harrosh <boaz@...xistor.com>
Cc:	Dave Chinner <david@...morbit.com>, Andrew Morton <akpm@...l.org>,
	x86@...nel.org, linux-nvdimm@...ts.01.org,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>, linux-fsdevel@...r.kernel.org,
	Christoph Hellwig <hch@....de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH] dax, pmem: add support for msync

On Wed, Sep 02, 2015 at 12:41:44PM +0300, Boaz Harrosh wrote:
> On 09/02/2015 12:37 PM, Boaz Harrosh wrote:
> >>  
> >> +               /*
> >> +                * Make sure that for VM_MIXEDMAP VMA has both
> >> +                * vm_ops->page_mkwrite and vm_ops->pfn_mkwrite or has none.
> >> +                */
> >> +               if ((vma->vm_ops->page_mkwrite || vma->vm_ops->pfn_mkwrite) &&
> >> +                               vma->vm_flags & VM_MIXEDMAP) {
> >> +                       VM_BUG_ON_VMA(!vma->vm_ops->page_mkwrite, vma);
> >> +                       VM_BUG_ON_VMA(!vma->vm_ops->pfn_mkwrite, vma);
> > 
> > BTW: the page_mkwrite is used for reading of holes that put zero-pages at the radix tree.
> >      One can just map a single global zero-page in pfn-mode for that.
> > 
> > Kirill Hi. Please don't make these BUG_ONs its counter productive believe me.

This is VM_BUG_ON, not normal BUG_ON. VM_BUG_ON is under CONFIG_DEBUG_VM 
which is disabled on production kernels.

> > Please make them WARN_ON_ONCE() it is not a crashing bug to work like this.
> > (Actually it is not a bug at all in some cases, but we can relax that when a user
> >  comes up)
> > 
> > Thanks
> > Boaz
> > 
> 
> Second thought I do not like this patch. This is why we have xftests for, the fact of it
> is that test 080 catches this. For me this is enough.

I don't insist on applying the patch. And I worry about false-positives.

> An FS developer should test his code, and worst case we help him on ML, like we did
> in this case.
> 
> Thanks
> Boaz
> 
> >> +               }
> >>                 addr = vma->vm_start;
> >>                 vm_flags = vma->vm_flags;
> >>         } else if (vm_flags & VM_SHARED) {
> >>
> > 
> 

-- 
 Kirill A. Shutemov
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