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authorLinus Torvalds <torvalds@linux-foundation.org>2016-03-19 05:26:54 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2016-03-19 05:26:54 +0300
commit814a2bf957739f367cbebfa1b60237387b72d0ee (patch)
tree8d65c38d14beb8d6d2dc5b9d7f8dbe63c7cad31a /tools/testing/radix-tree/regression1.c
parent237045fc3c67d44088f767dca5a9fa30815eba62 (diff)
parentf9310b2f9a19b7f16c7b1c1558f8b649b9b933c1 (diff)
downloadlinux-814a2bf957739f367cbebfa1b60237387b72d0ee.tar.xz
Merge branch 'akpm' (patches from Andrew)
Merge second patch-bomb from Andrew Morton: - a couple of hotfixes - the rest of MM - a new timer slack control in procfs - a couple of procfs fixes - a few misc things - some printk tweaks - lib/ updates, notably to radix-tree. - add my and Nick Piggin's old userspace radix-tree test harness to tools/testing/radix-tree/. Matthew said it was a godsend during the radix-tree work he did. - a few code-size improvements, switching to __always_inline where gcc screwed up. - partially implement character sets in sscanf * emailed patches from Andrew Morton <akpm@linux-foundation.org>: (118 commits) sscanf: implement basic character sets lib/bug.c: use common WARN helper param: convert some "on"/"off" users to strtobool lib: add "on"/"off" support to kstrtobool lib: update single-char callers of strtobool() lib: move strtobool() to kstrtobool() include/linux/unaligned: force inlining of byteswap operations include/uapi/linux/byteorder, swab: force inlining of some byteswap operations include/asm-generic/atomic-long.h: force inlining of some atomic_long operations usb: common: convert to use match_string() helper ide: hpt366: convert to use match_string() helper ata: hpt366: convert to use match_string() helper power: ab8500: convert to use match_string() helper power: charger_manager: convert to use match_string() helper drm/edid: convert to use match_string() helper pinctrl: convert to use match_string() helper device property: convert to use match_string() helper lib/string: introduce match_string() helper radix-tree tests: add test for radix_tree_iter_next radix-tree tests: add regression3 test ...
Diffstat (limited to 'tools/testing/radix-tree/regression1.c')
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diff --git a/tools/testing/radix-tree/regression1.c b/tools/testing/radix-tree/regression1.c
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+++ b/tools/testing/radix-tree/regression1.c
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+/*
+ * Regression1
+ * Description:
+ * Salman Qazi describes the following radix-tree bug:
+ *
+ * In the following case, we get can get a deadlock:
+ *
+ * 0. The radix tree contains two items, one has the index 0.
+ * 1. The reader (in this case find_get_pages) takes the rcu_read_lock.
+ * 2. The reader acquires slot(s) for item(s) including the index 0 item.
+ * 3. The non-zero index item is deleted, and as a consequence the other item
+ * is moved to the root of the tree. The place where it used to be is queued
+ * for deletion after the readers finish.
+ * 3b. The zero item is deleted, removing it from the direct slot, it remains in
+ * the rcu-delayed indirect node.
+ * 4. The reader looks at the index 0 slot, and finds that the page has 0 ref
+ * count
+ * 5. The reader looks at it again, hoping that the item will either be freed
+ * or the ref count will increase. This never happens, as the slot it is
+ * looking at will never be updated. Also, this slot can never be reclaimed
+ * because the reader is holding rcu_read_lock and is in an infinite loop.
+ *
+ * The fix is to re-use the same "indirect" pointer case that requires a slot
+ * lookup retry into a general "retry the lookup" bit.
+ *
+ * Running:
+ * This test should run to completion in a few seconds. The above bug would
+ * cause it to hang indefinitely.
+ *
+ * Upstream commit:
+ * Not yet
+ */
+#include <linux/kernel.h>
+#include <linux/gfp.h>
+#include <linux/slab.h>
+#include <linux/radix-tree.h>
+#include <linux/rcupdate.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <assert.h>
+
+#include "regression.h"
+
+static RADIX_TREE(mt_tree, GFP_KERNEL);
+static pthread_mutex_t mt_lock;
+
+struct page {
+ pthread_mutex_t lock;
+ struct rcu_head rcu;
+ int count;
+ unsigned long index;
+};
+
+static struct page *page_alloc(void)
+{
+ struct page *p;
+ p = malloc(sizeof(struct page));
+ p->count = 1;
+ p->index = 1;
+ pthread_mutex_init(&p->lock, NULL);
+
+ return p;
+}
+
+static void page_rcu_free(struct rcu_head *rcu)
+{
+ struct page *p = container_of(rcu, struct page, rcu);
+ assert(!p->count);
+ pthread_mutex_destroy(&p->lock);
+ free(p);
+}
+
+static void page_free(struct page *p)
+{
+ call_rcu(&p->rcu, page_rcu_free);
+}
+
+static unsigned find_get_pages(unsigned long start,
+ unsigned int nr_pages, struct page **pages)
+{
+ unsigned int i;
+ unsigned int ret;
+ unsigned int nr_found;
+
+ rcu_read_lock();
+restart:
+ nr_found = radix_tree_gang_lookup_slot(&mt_tree,
+ (void ***)pages, NULL, start, nr_pages);
+ ret = 0;
+ for (i = 0; i < nr_found; i++) {
+ struct page *page;
+repeat:
+ page = radix_tree_deref_slot((void **)pages[i]);
+ if (unlikely(!page))
+ continue;
+
+ if (radix_tree_exception(page)) {
+ if (radix_tree_deref_retry(page)) {
+ /*
+ * Transient condition which can only trigger
+ * when entry at index 0 moves out of or back
+ * to root: none yet gotten, safe to restart.
+ */
+ assert((start | i) == 0);
+ goto restart;
+ }
+ /*
+ * No exceptional entries are inserted in this test.
+ */
+ assert(0);
+ }
+
+ pthread_mutex_lock(&page->lock);
+ if (!page->count) {
+ pthread_mutex_unlock(&page->lock);
+ goto repeat;
+ }
+ /* don't actually update page refcount */
+ pthread_mutex_unlock(&page->lock);
+
+ /* Has the page moved? */
+ if (unlikely(page != *((void **)pages[i]))) {
+ goto repeat;
+ }
+
+ pages[ret] = page;
+ ret++;
+ }
+ rcu_read_unlock();
+ return ret;
+}
+
+static pthread_barrier_t worker_barrier;
+
+static void *regression1_fn(void *arg)
+{
+ rcu_register_thread();
+
+ if (pthread_barrier_wait(&worker_barrier) ==
+ PTHREAD_BARRIER_SERIAL_THREAD) {
+ int j;
+
+ for (j = 0; j < 1000000; j++) {
+ struct page *p;
+
+ p = page_alloc();
+ pthread_mutex_lock(&mt_lock);
+ radix_tree_insert(&mt_tree, 0, p);
+ pthread_mutex_unlock(&mt_lock);
+
+ p = page_alloc();
+ pthread_mutex_lock(&mt_lock);
+ radix_tree_insert(&mt_tree, 1, p);
+ pthread_mutex_unlock(&mt_lock);
+
+ pthread_mutex_lock(&mt_lock);
+ p = radix_tree_delete(&mt_tree, 1);
+ pthread_mutex_lock(&p->lock);
+ p->count--;
+ pthread_mutex_unlock(&p->lock);
+ pthread_mutex_unlock(&mt_lock);
+ page_free(p);
+
+ pthread_mutex_lock(&mt_lock);
+ p = radix_tree_delete(&mt_tree, 0);
+ pthread_mutex_lock(&p->lock);
+ p->count--;
+ pthread_mutex_unlock(&p->lock);
+ pthread_mutex_unlock(&mt_lock);
+ page_free(p);
+ }
+ } else {
+ int j;
+
+ for (j = 0; j < 100000000; j++) {
+ struct page *pages[10];
+
+ find_get_pages(0, 10, pages);
+ }
+ }
+
+ rcu_unregister_thread();
+
+ return NULL;
+}
+
+static pthread_t *threads;
+void regression1_test(void)
+{
+ int nr_threads;
+ int i;
+ long arg;
+
+ /* Regression #1 */
+ printf("running regression test 1, should finish in under a minute\n");
+ nr_threads = 2;
+ pthread_barrier_init(&worker_barrier, NULL, nr_threads);
+
+ threads = malloc(nr_threads * sizeof(pthread_t *));
+
+ for (i = 0; i < nr_threads; i++) {
+ arg = i;
+ if (pthread_create(&threads[i], NULL, regression1_fn, (void *)arg)) {
+ perror("pthread_create");
+ exit(1);
+ }
+ }
+
+ for (i = 0; i < nr_threads; i++) {
+ if (pthread_join(threads[i], NULL)) {
+ perror("pthread_join");
+ exit(1);
+ }
+ }
+
+ free(threads);
+
+ printf("regression test 1, done\n");
+}