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Revision 4adaa611020fa6ac65b0ac8db78276af4ec04e63 authored by Chris Mason on 26 March 2013, 17:07:00 UTC, committed by Chris Mason on 26 March 2013, 17:19:14 UTC 
Btrfs: fix race between mmap writes and compression
 
Btrfs uses page_mkwrite to ensure stable pages during
crc calculations and mmap workloads.  We call clear_page_dirty_for_io
before we do any crcs, and this forces any application with the file
mapped to wait for the crc to finish before it is allowed to change
the file.

With compression on, the clear_page_dirty_for_io step is happening after
we've compressed the pages.  This means the applications might be
changing the pages while we are compressing them, and some of those
modifications might not hit the disk.

This commit adds the clear_page_dirty_for_io before compression starts
and makes sure to redirty the page if we have to fallback to
uncompressed IO as well.

Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Reported-by: Alexandre Oliva <oliva@gnu.org>
cc: stable@vger.kernel.org
1 parent 1dd0568
Raw File
generic_mpih-add1.c 
/* mpihelp-add_1.c  -  MPI helper functions
 * Copyright (C) 1994, 1996, 1997, 1998,
 *               2000 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 *
 * Note: This code is heavily based on the GNU MP Library.
 *	 Actually it's the same code with only minor changes in the
 *	 way the data is stored; this is to support the abstraction
 *	 of an optional secure memory allocation which may be used
 *	 to avoid revealing of sensitive data due to paging etc.
 *	 The GNU MP Library itself is published under the LGPL;
 *	 however I decided to publish this code under the plain GPL.
 */

#include "mpi-internal.h"
#include "longlong.h"

mpi_limb_t
mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
	      mpi_ptr_t s2_ptr, mpi_size_t size)
{
	mpi_limb_t x, y, cy;
	mpi_size_t j;

	/* The loop counter and index J goes from -SIZE to -1.  This way
	   the loop becomes faster.  */
	j = -size;

	/* Offset the base pointers to compensate for the negative indices. */
	s1_ptr -= j;
	s2_ptr -= j;
	res_ptr -= j;

	cy = 0;
	do {
		y = s2_ptr[j];
		x = s1_ptr[j];
		y += cy;	/* add previous carry to one addend */
		cy = y < cy;	/* get out carry from that addition */
		y += x;		/* add other addend */
		cy += y < x;	/* get out carry from that add, combine */
		res_ptr[j] = y;
	} while (++j);

	return cy;
}
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