linux-kernel - Re: [BUG] bug when enabling VM DEBUG

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Date:	Wed, 12 May 2010 13:53:40 +0200
From:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Robert Hancock <hancockrwd@...il.com>,
	saeed bishara <saeed.bishara@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	DE/ATA development list <linux-ide@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>,
	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Subject: Re: [BUG] bug when enabling VM DEBUG

* Catalin Marinas | 2010-05-12 12:10:39 [+0100]:

>> > --- a/drivers/ata/libata-sff.c
>> > +++ b/drivers/ata/libata-sff.c
>> > @@ -894,7 +894,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
>> >                                         do_write);
>> >          }
>> >
>> > -       if (!do_write)
>> > +       if (!do_write&&  !PageSlab(page))
>> >                  flush_dcache_page(page);
>> 
>> I would think that check belongs inside flush_dcache_page itself, rather
>> than forcing every driver to include it..
>
>Sebastian (cc'ed) reported this as well for MIPS.
Thx. The patch above looks what I've sent a while ago. Jeff was going to
merge it afaik.

>I think it makes sense for this check to be done in the
>flush_dcache_page() function.

Why should flush_dcache_page() not flush pages you tell it?
>From Documentation/cachetlb.txt:
|   NOTE: This routine need only be called for page cache pages
|          which can potentially ever be mapped into the address
|          space of a user process.  So for example, VFS layer code
|          handling vfs symlinks in the page cache need not call
|          this interface at all.

A page from slab or stack is not going to see the sky of user land and
therefore it should not be fed into flush_dcache_page().

Sebastian
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