linux-kernel - Re: another pmem variant V2

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Message-ID: <20150402093721.GD14209@lst.de>
Date:	Thu, 2 Apr 2015 11:37:21 +0200
From:	Christoph Hellwig <hch@....de>
To:	"Elliott, Robert (Server Storage)" <Elliott@...com>
Cc:	Christoph Hellwig <hch@....de>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
	"axboe@...nel.dk" <axboe@...nel.dk>,
	"boaz@...xistor.com" <boaz@...xistor.com>,
	"Kani, Toshimitsu" <toshi.kani@...com>
Subject: Re: another pmem variant V2

On Wed, Apr 01, 2015 at 07:33:38PM +0000, Elliott, Robert (Server Storage) wrote:
> I triggered a paging error in the memcpy call for a block read
> from system-udevd (actually in a modified memcpy() for the cache
> attribute experiments).  
> 
> 1. This triggered an illegal schedule() call from an atomic context.
> The call trace is shown below.
> 
> 2. memcpy() doesn't provide exception handling or error reporting.
> Some functions like do so, like __copy_user_nocache in
> arch/x85/lib/copy_user_nocache_64.S.  
> 
> Should pmem only use functions that do so, if available on the
> architecture?

We'll need to define an interface for the function to use if it isn't
plain memcpy, which would include that detail.

But I can't see how that memcpy should ever have to handle a page fault,
I'd be curious how your reproduces this issue.
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