Revision e2093926a098a8ccf0f1d10f6df8dad452cb28d3 authored by Ross Zwisler on 02 June 2017, 21:46:37 UTC, committed by Linus Torvalds on 02 June 2017, 22:07:37 UTC
We currently have two related PMD vs PTE races in the DAX code. These can both be easily triggered by having two threads reading and writing simultaneously to the same private mapping, with the key being that private mapping reads can be handled with PMDs but private mapping writes are always handled with PTEs so that we can COW. Here is the first race: CPU 0 CPU 1 (private mapping write) __handle_mm_fault() create_huge_pmd() - FALLBACK handle_pte_fault() passes check for pmd_devmap() (private mapping read) __handle_mm_fault() create_huge_pmd() dax_iomap_pmd_fault() inserts PMD dax_iomap_pte_fault() does a PTE fault, but we already have a DAX PMD installed in our page tables at this spot. Here's the second race: CPU 0 CPU 1 (private mapping read) __handle_mm_fault() passes check for pmd_none() create_huge_pmd() dax_iomap_pmd_fault() inserts PMD (private mapping write) __handle_mm_fault() create_huge_pmd() - FALLBACK (private mapping read) __handle_mm_fault() passes check for pmd_none() create_huge_pmd() handle_pte_fault() dax_iomap_pte_fault() inserts PTE dax_iomap_pmd_fault() inserts PMD, but we already have a PTE at this spot. The core of the issue is that while there is isolation between faults to the same range in the DAX fault handlers via our DAX entry locking, there is no isolation between faults in the code in mm/memory.c. This means for instance that this code in __handle_mm_fault() can run: if (pmd_none(*vmf.pmd) && transparent_hugepage_enabled(vma)) { ret = create_huge_pmd(&vmf); But by the time we actually get to run the fault handler called by create_huge_pmd(), the PMD is no longer pmd_none() because a racing PTE fault has installed a normal PMD here as a parent. This is the cause of the 2nd race. The first race is similar - there is the following check in handle_pte_fault(): } else { /* See comment in pte_alloc_one_map() */ if (pmd_devmap(*vmf->pmd) || pmd_trans_unstable(vmf->pmd)) return 0; So if a pmd_devmap() PMD (a DAX PMD) has been installed at vmf->pmd, we will bail and retry the fault. This is correct, but there is nothing preventing the PMD from being installed after this check but before we actually get to the DAX PTE fault handlers. In my testing these races result in the following types of errors: BUG: Bad rss-counter state mm:ffff8800a817d280 idx:1 val:1 BUG: non-zero nr_ptes on freeing mm: 15 Fix this issue by having the DAX fault handlers verify that it is safe to continue their fault after they have taken an entry lock to block other racing faults. [ross.zwisler@linux.intel.com: improve fix for colliding PMD & PTE entries] Link: http://lkml.kernel.org/r/20170526195932.32178-1-ross.zwisler@linux.intel.com Link: http://lkml.kernel.org/r/20170522215749.23516-2-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> Reported-by: Pawel Lebioda <pawel.lebioda@intel.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: "Darrick J. Wong" <darrick.wong@oracle.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@lst.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Matthew Wilcox <mawilcox@microsoft.com> Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com> Cc: Pawel Lebioda <pawel.lebioda@intel.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Xiong Zhou <xzhou@redhat.com> Cc: Eryu Guan <eguan@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent d0f0931
fdtget.c
/*
* Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
*
* Portions from U-Boot cmd_fdt.c (C) Copyright 2007
* Gerald Van Baren, Custom IDEAS, vanbaren@cideas.com
* Based on code written by:
* Pantelis Antoniou <pantelis.antoniou@gmail.com> and
* Matthew McClintock <msm@freescale.com>
*
* This program 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.
*
* This program 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
*/
#include <assert.h>
#include <ctype.h>
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libfdt.h>
#include "util.h"
enum display_mode {
MODE_SHOW_VALUE, /* show values for node properties */
MODE_LIST_PROPS, /* list the properties for a node */
MODE_LIST_SUBNODES, /* list the subnodes of a node */
};
/* Holds information which controls our output and options */
struct display_info {
int type; /* data type (s/i/u/x or 0 for default) */
int size; /* data size (1/2/4) */
enum display_mode mode; /* display mode that we are using */
const char *default_val; /* default value if node/property not found */
};
static void report_error(const char *where, int err)
{
fprintf(stderr, "Error at '%s': %s\n", where, fdt_strerror(err));
}
/**
* Displays data of a given length according to selected options
*
* If a specific data type is provided in disp, then this is used. Otherwise
* we try to guess the data type / size from the contents.
*
* @param disp Display information / options
* @param data Data to display
* @param len Maximum length of buffer
* @return 0 if ok, -1 if data does not match format
*/
static int show_data(struct display_info *disp, const char *data, int len)
{
int i, size;
const uint8_t *p = (const uint8_t *)data;
const char *s;
int value;
int is_string;
char fmt[3];
/* no data, don't print */
if (len == 0)
return 0;
is_string = (disp->type) == 's' ||
(!disp->type && util_is_printable_string(data, len));
if (is_string) {
if (data[len - 1] != '\0') {
fprintf(stderr, "Unterminated string\n");
return -1;
}
for (s = data; s - data < len; s += strlen(s) + 1) {
if (s != data)
printf(" ");
printf("%s", (const char *)s);
}
return 0;
}
size = disp->size;
if (size == -1) {
size = (len % 4) == 0 ? 4 : 1;
} else if (len % size) {
fprintf(stderr, "Property length must be a multiple of "
"selected data size\n");
return -1;
}
fmt[0] = '%';
fmt[1] = disp->type ? disp->type : 'd';
fmt[2] = '\0';
for (i = 0; i < len; i += size, p += size) {
if (i)
printf(" ");
value = size == 4 ? fdt32_to_cpu(*(const uint32_t *)p) :
size == 2 ? (*p << 8) | p[1] : *p;
printf(fmt, value);
}
return 0;
}
/**
* List all properties in a node, one per line.
*
* @param blob FDT blob
* @param node Node to display
* @return 0 if ok, or FDT_ERR... if not.
*/
static int list_properties(const void *blob, int node)
{
const struct fdt_property *data;
const char *name;
int prop;
prop = fdt_first_property_offset(blob, node);
do {
/* Stop silently when there are no more properties */
if (prop < 0)
return prop == -FDT_ERR_NOTFOUND ? 0 : prop;
data = fdt_get_property_by_offset(blob, prop, NULL);
name = fdt_string(blob, fdt32_to_cpu(data->nameoff));
if (name)
puts(name);
prop = fdt_next_property_offset(blob, prop);
} while (1);
}
#define MAX_LEVEL 32 /* how deeply nested we will go */
/**
* List all subnodes in a node, one per line
*
* @param blob FDT blob
* @param node Node to display
* @return 0 if ok, or FDT_ERR... if not.
*/
static int list_subnodes(const void *blob, int node)
{
int nextoffset; /* next node offset from libfdt */
uint32_t tag; /* current tag */
int level = 0; /* keep track of nesting level */
const char *pathp;
int depth = 1; /* the assumed depth of this node */
while (level >= 0) {
tag = fdt_next_tag(blob, node, &nextoffset);
switch (tag) {
case FDT_BEGIN_NODE:
pathp = fdt_get_name(blob, node, NULL);
if (level <= depth) {
if (pathp == NULL)
pathp = "/* NULL pointer error */";
if (*pathp == '\0')
pathp = "/"; /* root is nameless */
if (level == 1)
puts(pathp);
}
level++;
if (level >= MAX_LEVEL) {
printf("Nested too deep, aborting.\n");
return 1;
}
break;
case FDT_END_NODE:
level--;
if (level == 0)
level = -1; /* exit the loop */
break;
case FDT_END:
return 1;
case FDT_PROP:
break;
default:
if (level <= depth)
printf("Unknown tag 0x%08X\n", tag);
return 1;
}
node = nextoffset;
}
return 0;
}
/**
* Show the data for a given node (and perhaps property) according to the
* display option provided.
*
* @param blob FDT blob
* @param disp Display information / options
* @param node Node to display
* @param property Name of property to display, or NULL if none
* @return 0 if ok, -ve on error
*/
static int show_data_for_item(const void *blob, struct display_info *disp,
int node, const char *property)
{
const void *value = NULL;
int len, err = 0;
switch (disp->mode) {
case MODE_LIST_PROPS:
err = list_properties(blob, node);
break;
case MODE_LIST_SUBNODES:
err = list_subnodes(blob, node);
break;
default:
assert(property);
value = fdt_getprop(blob, node, property, &len);
if (value) {
if (show_data(disp, value, len))
err = -1;
else
printf("\n");
} else if (disp->default_val) {
puts(disp->default_val);
} else {
report_error(property, len);
err = -1;
}
break;
}
return err;
}
/**
* Run the main fdtget operation, given a filename and valid arguments
*
* @param disp Display information / options
* @param filename Filename of blob file
* @param arg List of arguments to process
* @param arg_count Number of arguments
* @param return 0 if ok, -ve on error
*/
static int do_fdtget(struct display_info *disp, const char *filename,
char **arg, int arg_count, int args_per_step)
{
char *blob;
const char *prop;
int i, node;
blob = utilfdt_read(filename);
if (!blob)
return -1;
for (i = 0; i + args_per_step <= arg_count; i += args_per_step) {
node = fdt_path_offset(blob, arg[i]);
if (node < 0) {
if (disp->default_val) {
puts(disp->default_val);
continue;
} else {
report_error(arg[i], node);
return -1;
}
}
prop = args_per_step == 1 ? NULL : arg[i + 1];
if (show_data_for_item(blob, disp, node, prop))
return -1;
}
return 0;
}
static const char *usage_msg =
"fdtget - read values from device tree\n"
"\n"
"Each value is printed on a new line.\n\n"
"Usage:\n"
" fdtget <options> <dt file> [<node> <property>]...\n"
" fdtget -p <options> <dt file> [<node> ]...\n"
"Options:\n"
"\t-t <type>\tType of data\n"
"\t-p\t\tList properties for each node\n"
"\t-l\t\tList subnodes for each node\n"
"\t-d\t\tDefault value to display when the property is "
"missing\n"
"\t-h\t\tPrint this help\n\n"
USAGE_TYPE_MSG;
static void usage(const char *msg)
{
if (msg)
fprintf(stderr, "Error: %s\n\n", msg);
fprintf(stderr, "%s", usage_msg);
exit(2);
}
int main(int argc, char *argv[])
{
char *filename = NULL;
struct display_info disp;
int args_per_step = 2;
/* set defaults */
memset(&disp, '\0', sizeof(disp));
disp.size = -1;
disp.mode = MODE_SHOW_VALUE;
for (;;) {
int c = getopt(argc, argv, "d:hlpt:");
if (c == -1)
break;
switch (c) {
case 'h':
case '?':
usage(NULL);
case 't':
if (utilfdt_decode_type(optarg, &disp.type,
&disp.size))
usage("Invalid type string");
break;
case 'p':
disp.mode = MODE_LIST_PROPS;
args_per_step = 1;
break;
case 'l':
disp.mode = MODE_LIST_SUBNODES;
args_per_step = 1;
break;
case 'd':
disp.default_val = optarg;
break;
}
}
if (optind < argc)
filename = argv[optind++];
if (!filename)
usage("Missing filename");
argv += optind;
argc -= optind;
/* Allow no arguments, and silently succeed */
if (!argc)
return 0;
/* Check for node, property arguments */
if (args_per_step == 2 && (argc % 2))
usage("Must have an even number of arguments");
if (do_fdtget(&disp, filename, argv, argc, args_per_step))
return 1;
return 0;
}
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