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>
1 parent bc448e8
textsearch.c
/*
* lib/textsearch.c Generic text search interface
*
* 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.
*
* Authors: Thomas Graf <tgraf@suug.ch>
* Pablo Neira Ayuso <pablo@netfilter.org>
*
* ==========================================================================
*
* INTRODUCTION
*
* The textsearch infrastructure provides text searching facilities for
* both linear and non-linear data. Individual search algorithms are
* implemented in modules and chosen by the user.
*
* ARCHITECTURE
*
* User
* +----------------+
* | finish()|<--------------(6)-----------------+
* |get_next_block()|<--------------(5)---------------+ |
* | | Algorithm | |
* | | +------------------------------+
* | | | init() find() destroy() |
* | | +------------------------------+
* | | Core API ^ ^ ^
* | | +---------------+ (2) (4) (8)
* | (1)|----->| prepare() |---+ | |
* | (3)|----->| find()/next() |-----------+ |
* | (7)|----->| destroy() |----------------------+
* +----------------+ +---------------+
*
* (1) User configures a search by calling _prepare() specifying the
* search parameters such as the pattern and algorithm name.
* (2) Core requests the algorithm to allocate and initialize a search
* configuration according to the specified parameters.
* (3) User starts the search(es) by calling _find() or _next() to
* fetch subsequent occurrences. A state variable is provided
* to the algorithm to store persistent variables.
* (4) Core eventually resets the search offset and forwards the find()
* request to the algorithm.
* (5) Algorithm calls get_next_block() provided by the user continuously
* to fetch the data to be searched in block by block.
* (6) Algorithm invokes finish() after the last call to get_next_block
* to clean up any leftovers from get_next_block. (Optional)
* (7) User destroys the configuration by calling _destroy().
* (8) Core notifies the algorithm to destroy algorithm specific
* allocations. (Optional)
*
* USAGE
*
* Before a search can be performed, a configuration must be created
* by calling textsearch_prepare() specifying the searching algorithm,
* the pattern to look for and flags. As a flag, you can set TS_IGNORECASE
* to perform case insensitive matching. But it might slow down
* performance of algorithm, so you should use it at own your risk.
* The returned configuration may then be used for an arbitrary
* amount of times and even in parallel as long as a separate struct
* ts_state variable is provided to every instance.
*
* The actual search is performed by either calling textsearch_find_-
* continuous() for linear data or by providing an own get_next_block()
* implementation and calling textsearch_find(). Both functions return
* the position of the first occurrence of the pattern or UINT_MAX if
* no match was found. Subsequent occurrences can be found by calling
* textsearch_next() regardless of the linearity of the data.
*
* Once you're done using a configuration it must be given back via
* textsearch_destroy.
*
* EXAMPLE
*
* int pos;
* struct ts_config *conf;
* struct ts_state state;
* const char *pattern = "chicken";
* const char *example = "We dance the funky chicken";
*
* conf = textsearch_prepare("kmp", pattern, strlen(pattern),
* GFP_KERNEL, TS_AUTOLOAD);
* if (IS_ERR(conf)) {
* err = PTR_ERR(conf);
* goto errout;
* }
*
* pos = textsearch_find_continuous(conf, &state, example, strlen(example));
* if (pos != UINT_MAX)
* panic("Oh my god, dancing chickens at %d\n", pos);
*
* textsearch_destroy(conf);
* ==========================================================================
*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <linux/err.h>
#include <linux/textsearch.h>
#include <linux/slab.h>
static LIST_HEAD(ts_ops);
static DEFINE_SPINLOCK(ts_mod_lock);
static inline struct ts_ops *lookup_ts_algo(const char *name)
{
struct ts_ops *o;
rcu_read_lock();
list_for_each_entry_rcu(o, &ts_ops, list) {
if (!strcmp(name, o->name)) {
if (!try_module_get(o->owner))
o = NULL;
rcu_read_unlock();
return o;
}
}
rcu_read_unlock();
return NULL;
}
/**
* textsearch_register - register a textsearch module
* @ops: operations lookup table
*
* This function must be called by textsearch modules to announce
* their presence. The specified &@ops must have %name set to a
* unique identifier and the callbacks find(), init(), get_pattern(),
* and get_pattern_len() must be implemented.
*
* Returns 0 or -EEXISTS if another module has already registered
* with same name.
*/
int textsearch_register(struct ts_ops *ops)
{
int err = -EEXIST;
struct ts_ops *o;
if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
ops->get_pattern == NULL || ops->get_pattern_len == NULL)
return -EINVAL;
spin_lock(&ts_mod_lock);
list_for_each_entry(o, &ts_ops, list) {
if (!strcmp(ops->name, o->name))
goto errout;
}
list_add_tail_rcu(&ops->list, &ts_ops);
err = 0;
errout:
spin_unlock(&ts_mod_lock);
return err;
}
EXPORT_SYMBOL(textsearch_register);
/**
* textsearch_unregister - unregister a textsearch module
* @ops: operations lookup table
*
* This function must be called by textsearch modules to announce
* their disappearance for examples when the module gets unloaded.
* The &ops parameter must be the same as the one during the
* registration.
*
* Returns 0 on success or -ENOENT if no matching textsearch
* registration was found.
*/
int textsearch_unregister(struct ts_ops *ops)
{
int err = 0;
struct ts_ops *o;
spin_lock(&ts_mod_lock);
list_for_each_entry(o, &ts_ops, list) {
if (o == ops) {
list_del_rcu(&o->list);
goto out;
}
}
err = -ENOENT;
out:
spin_unlock(&ts_mod_lock);
return err;
}
EXPORT_SYMBOL(textsearch_unregister);
struct ts_linear_state
{
unsigned int len;
const void *data;
};
static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
struct ts_config *conf,
struct ts_state *state)
{
struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
if (likely(consumed < st->len)) {
*dst = st->data + consumed;
return st->len - consumed;
}
return 0;
}
/**
* textsearch_find_continuous - search a pattern in continuous/linear data
* @conf: search configuration
* @state: search state
* @data: data to search in
* @len: length of data
*
* A simplified version of textsearch_find() for continuous/linear data.
* Call textsearch_next() to retrieve subsequent matches.
*
* Returns the position of first occurrence of the pattern or
* %UINT_MAX if no occurrence was found.
*/
unsigned int textsearch_find_continuous(struct ts_config *conf,
struct ts_state *state,
const void *data, unsigned int len)
{
struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
conf->get_next_block = get_linear_data;
st->data = data;
st->len = len;
return textsearch_find(conf, state);
}
EXPORT_SYMBOL(textsearch_find_continuous);
/**
* textsearch_prepare - Prepare a search
* @algo: name of search algorithm
* @pattern: pattern data
* @len: length of pattern
* @gfp_mask: allocation mask
* @flags: search flags
*
* Looks up the search algorithm module and creates a new textsearch
* configuration for the specified pattern.
*
* Note: The format of the pattern may not be compatible between
* the various search algorithms.
*
* Returns a new textsearch configuration according to the specified
* parameters or a ERR_PTR(). If a zero length pattern is passed, this
* function returns EINVAL.
*/
struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
unsigned int len, gfp_t gfp_mask, int flags)
{
int err = -ENOENT;
struct ts_config *conf;
struct ts_ops *ops;
if (len == 0)
return ERR_PTR(-EINVAL);
ops = lookup_ts_algo(algo);
#ifdef CONFIG_MODULES
/*
* Why not always autoload you may ask. Some users are
* in a situation where requesting a module may deadlock,
* especially when the module is located on a NFS mount.
*/
if (ops == NULL && flags & TS_AUTOLOAD) {
request_module("ts_%s", algo);
ops = lookup_ts_algo(algo);
}
#endif
if (ops == NULL)
goto errout;
conf = ops->init(pattern, len, gfp_mask, flags);
if (IS_ERR(conf)) {
err = PTR_ERR(conf);
goto errout;
}
conf->ops = ops;
return conf;
errout:
if (ops)
module_put(ops->owner);
return ERR_PTR(err);
}
EXPORT_SYMBOL(textsearch_prepare);
/**
* textsearch_destroy - destroy a search configuration
* @conf: search configuration
*
* Releases all references of the configuration and frees
* up the memory.
*/
void textsearch_destroy(struct ts_config *conf)
{
if (conf->ops) {
if (conf->ops->destroy)
conf->ops->destroy(conf);
module_put(conf->ops->owner);
}
kfree(conf);
}
EXPORT_SYMBOL(textsearch_destroy);
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