Revision 03049269de433cb5fe2859be9ae4469ceb1163ed authored by Michal Hocko on 25 March 2016, 21:20:33 UTC, committed by Linus Torvalds on 25 March 2016, 23:37:42 UTC
wake_oom_reaper has allowed only 1 oom victim to be queued. The main reason for that was the simplicity as other solutions would require some way of queuing. The current approach is racy and that was deemed sufficient as the oom_reaper is considered a best effort approach to help with oom handling when the OOM victim cannot terminate in a reasonable time. The race could lead to missing an oom victim which can get stuck out_of_memory wake_oom_reaper cmpxchg // OK oom_reaper oom_reap_task __oom_reap_task oom_victim terminates atomic_inc_not_zero // fail out_of_memory wake_oom_reaper cmpxchg // fails task_to_reap = NULL This race requires 2 OOM invocations in a short time period which is not very likely but certainly not impossible. E.g. the original victim might have not released a lot of memory for some reason. The situation would improve considerably if wake_oom_reaper used a more robust queuing. This is what this patch implements. This means adding oom_reaper_list list_head into task_struct (eat a hole before embeded thread_struct for that purpose) and a oom_reaper_lock spinlock for queuing synchronization. wake_oom_reaper will then add the task on the queue and oom_reaper will dequeue it. Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: Vladimir Davydov <vdavydov@virtuozzo.com> Cc: Andrea Argangeli <andrea@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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glob.c
#include <linux/module.h>
#include <linux/glob.h>
/*
* The only reason this code can be compiled as a module is because the
* ATA code that depends on it can be as well. In practice, they're
* both usually compiled in and the module overhead goes away.
*/
MODULE_DESCRIPTION("glob(7) matching");
MODULE_LICENSE("Dual MIT/GPL");
/**
* glob_match - Shell-style pattern matching, like !fnmatch(pat, str, 0)
* @pat: Shell-style pattern to match, e.g. "*.[ch]".
* @str: String to match. The pattern must match the entire string.
*
* Perform shell-style glob matching, returning true (1) if the match
* succeeds, or false (0) if it fails. Equivalent to !fnmatch(@pat, @str, 0).
*
* Pattern metacharacters are ?, *, [ and \.
* (And, inside character classes, !, - and ].)
*
* This is small and simple implementation intended for device blacklists
* where a string is matched against a number of patterns. Thus, it
* does not preprocess the patterns. It is non-recursive, and run-time
* is at most quadratic: strlen(@str)*strlen(@pat).
*
* An example of the worst case is glob_match("*aaaaa", "aaaaaaaaaa");
* it takes 6 passes over the pattern before matching the string.
*
* Like !fnmatch(@pat, @str, 0) and unlike the shell, this does NOT
* treat / or leading . specially; it isn't actually used for pathnames.
*
* Note that according to glob(7) (and unlike bash), character classes
* are complemented by a leading !; this does not support the regex-style
* [^a-z] syntax.
*
* An opening bracket without a matching close is matched literally.
*/
bool __pure glob_match(char const *pat, char const *str)
{
/*
* Backtrack to previous * on mismatch and retry starting one
* character later in the string. Because * matches all characters
* (no exception for /), it can be easily proved that there's
* never a need to backtrack multiple levels.
*/
char const *back_pat = NULL, *back_str = back_str;
/*
* Loop over each token (character or class) in pat, matching
* it against the remaining unmatched tail of str. Return false
* on mismatch, or true after matching the trailing nul bytes.
*/
for (;;) {
unsigned char c = *str++;
unsigned char d = *pat++;
switch (d) {
case '?': /* Wildcard: anything but nul */
if (c == '\0')
return false;
break;
case '*': /* Any-length wildcard */
if (*pat == '\0') /* Optimize trailing * case */
return true;
back_pat = pat;
back_str = --str; /* Allow zero-length match */
break;
case '[': { /* Character class */
bool match = false, inverted = (*pat == '!');
char const *class = pat + inverted;
unsigned char a = *class++;
/*
* Iterate over each span in the character class.
* A span is either a single character a, or a
* range a-b. The first span may begin with ']'.
*/
do {
unsigned char b = a;
if (a == '\0') /* Malformed */
goto literal;
if (class[0] == '-' && class[1] != ']') {
b = class[1];
if (b == '\0')
goto literal;
class += 2;
/* Any special action if a > b? */
}
match |= (a <= c && c <= b);
} while ((a = *class++) != ']');
if (match == inverted)
goto backtrack;
pat = class;
}
break;
case '\\':
d = *pat++;
/*FALLTHROUGH*/
default: /* Literal character */
literal:
if (c == d) {
if (d == '\0')
return true;
break;
}
backtrack:
if (c == '\0' || !back_pat)
return false; /* No point continuing */
/* Try again from last *, one character later in str. */
pat = back_pat;
str = ++back_str;
break;
}
}
}
EXPORT_SYMBOL(glob_match);
#ifdef CONFIG_GLOB_SELFTEST
#include <linux/printk.h>
#include <linux/moduleparam.h>
/* Boot with "glob.verbose=1" to show successful tests, too */
static bool verbose = false;
module_param(verbose, bool, 0);
struct glob_test {
char const *pat, *str;
bool expected;
};
static bool __pure __init test(char const *pat, char const *str, bool expected)
{
bool match = glob_match(pat, str);
bool success = match == expected;
/* Can't get string literals into a particular section, so... */
static char const msg_error[] __initconst =
KERN_ERR "glob: \"%s\" vs. \"%s\": %s *** ERROR ***\n";
static char const msg_ok[] __initconst =
KERN_DEBUG "glob: \"%s\" vs. \"%s\": %s OK\n";
static char const mismatch[] __initconst = "mismatch";
char const *message;
if (!success)
message = msg_error;
else if (verbose)
message = msg_ok;
else
return success;
printk(message, pat, str, mismatch + 3*match);
return success;
}
/*
* The tests are all jammed together in one array to make it simpler
* to place that array in the .init.rodata section. The obvious
* "array of structures containing char *" has no way to force the
* pointed-to strings to be in a particular section.
*
* Anyway, a test consists of:
* 1. Expected glob_match result: '1' or '0'.
* 2. Pattern to match: null-terminated string
* 3. String to match against: null-terminated string
*
* The list of tests is terminated with a final '\0' instead of
* a glob_match result character.
*/
static char const glob_tests[] __initconst =
/* Some basic tests */
"1" "a\0" "a\0"
"0" "a\0" "b\0"
"0" "a\0" "aa\0"
"0" "a\0" "\0"
"1" "\0" "\0"
"0" "\0" "a\0"
/* Simple character class tests */
"1" "[a]\0" "a\0"
"0" "[a]\0" "b\0"
"0" "[!a]\0" "a\0"
"1" "[!a]\0" "b\0"
"1" "[ab]\0" "a\0"
"1" "[ab]\0" "b\0"
"0" "[ab]\0" "c\0"
"1" "[!ab]\0" "c\0"
"1" "[a-c]\0" "b\0"
"0" "[a-c]\0" "d\0"
/* Corner cases in character class parsing */
"1" "[a-c-e-g]\0" "-\0"
"0" "[a-c-e-g]\0" "d\0"
"1" "[a-c-e-g]\0" "f\0"
"1" "[]a-ceg-ik[]\0" "a\0"
"1" "[]a-ceg-ik[]\0" "]\0"
"1" "[]a-ceg-ik[]\0" "[\0"
"1" "[]a-ceg-ik[]\0" "h\0"
"0" "[]a-ceg-ik[]\0" "f\0"
"0" "[!]a-ceg-ik[]\0" "h\0"
"0" "[!]a-ceg-ik[]\0" "]\0"
"1" "[!]a-ceg-ik[]\0" "f\0"
/* Simple wild cards */
"1" "?\0" "a\0"
"0" "?\0" "aa\0"
"0" "??\0" "a\0"
"1" "?x?\0" "axb\0"
"0" "?x?\0" "abx\0"
"0" "?x?\0" "xab\0"
/* Asterisk wild cards (backtracking) */
"0" "*??\0" "a\0"
"1" "*??\0" "ab\0"
"1" "*??\0" "abc\0"
"1" "*??\0" "abcd\0"
"0" "??*\0" "a\0"
"1" "??*\0" "ab\0"
"1" "??*\0" "abc\0"
"1" "??*\0" "abcd\0"
"0" "?*?\0" "a\0"
"1" "?*?\0" "ab\0"
"1" "?*?\0" "abc\0"
"1" "?*?\0" "abcd\0"
"1" "*b\0" "b\0"
"1" "*b\0" "ab\0"
"0" "*b\0" "ba\0"
"1" "*b\0" "bb\0"
"1" "*b\0" "abb\0"
"1" "*b\0" "bab\0"
"1" "*bc\0" "abbc\0"
"1" "*bc\0" "bc\0"
"1" "*bc\0" "bbc\0"
"1" "*bc\0" "bcbc\0"
/* Multiple asterisks (complex backtracking) */
"1" "*ac*\0" "abacadaeafag\0"
"1" "*ac*ae*ag*\0" "abacadaeafag\0"
"1" "*a*b*[bc]*[ef]*g*\0" "abacadaeafag\0"
"0" "*a*b*[ef]*[cd]*g*\0" "abacadaeafag\0"
"1" "*abcd*\0" "abcabcabcabcdefg\0"
"1" "*ab*cd*\0" "abcabcabcabcdefg\0"
"1" "*abcd*abcdef*\0" "abcabcdabcdeabcdefg\0"
"0" "*abcd*\0" "abcabcabcabcefg\0"
"0" "*ab*cd*\0" "abcabcabcabcefg\0";
static int __init glob_init(void)
{
unsigned successes = 0;
unsigned n = 0;
char const *p = glob_tests;
static char const message[] __initconst =
KERN_INFO "glob: %u self-tests passed, %u failed\n";
/*
* Tests are jammed together in a string. The first byte is '1'
* or '0' to indicate the expected outcome, or '\0' to indicate the
* end of the tests. Then come two null-terminated strings: the
* pattern and the string to match it against.
*/
while (*p) {
bool expected = *p++ & 1;
char const *pat = p;
p += strlen(p) + 1;
successes += test(pat, p, expected);
p += strlen(p) + 1;
n++;
}
n -= successes;
printk(message, successes, n);
/* What's the errno for "kernel bug detected"? Guess... */
return n ? -ECANCELED : 0;
}
/* We need a dummy exit function to allow unload */
static void __exit glob_fini(void) { }
module_init(glob_init);
module_exit(glob_fini);
#endif /* CONFIG_GLOB_SELFTEST */
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