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cgroup/dmem: Don't open-code css_for_each_descendant_pre 

The current implementation has a bug: If the current css doesn't
contain any pool that is a descendant of the "pool" (i.e. when
found_descendant == false), then "pool" will point to some unrelated
pool. If the current css has a child, we'll overwrite parent_pool with
this unrelated pool on the next iteration.

Since we can just check whether a pool refers to the same region to
determine whether or not it's related, all the additional pool tracking
is unnecessary, so just switch to using css_for_each_descendant_pre for
traversal.

Fixes: b168ed458d ("kernel/cgroup: Add "dmem" memory accounting cgroup")
Signed-off-by: Friedrich Vock <friedrich.vock@gmx.de>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250127152754.21325-1-friedrich.vock@gmx.de
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
This commit is contained in:
Friedrich Vock 2025-01-27 16:27:52 +01:00 committed by Maarten Lankhorst
parent b3fefbb30a
commit 8821f36333
1 changed files with 11 additions and 39 deletions
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50
kernel/cgroup/dmem.c
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@ -220,60 +220,32 @@ dmem_cgroup_calculate_protection(struct dmem_cgroup_pool_state *limit_pool,
struct dmem_cgroup_pool_state *test_pool)
{
struct page_counter *climit;
struct cgroup_subsys_state *css, *next_css;
struct cgroup_subsys_state *css;
struct dmemcg_state *dmemcg_iter;
struct dmem_cgroup_pool_state *pool, *parent_pool;
bool found_descendant;
struct dmem_cgroup_pool_state *pool, *found_pool;
climit = &limit_pool->cnt;
rcu_read_lock();
parent_pool = pool = limit_pool;
css = &limit_pool->cs->css;
/*
* This logic is roughly equivalent to css_foreach_descendant_pre,
* except we also track the parent pool to find out which pool we need
* to calculate protection values for.
*
* We can stop the traversal once we find test_pool among the
* descendants since we don't really care about any others.
*/
while (pool != test_pool) {
next_css = css_next_child(NULL, css);
if (next_css) {
parent_pool = pool;
} else {
while (css != &limit_pool->cs->css) {
next_css = css_next_child(css, css->parent);
if (next_css)
break;
css = css->parent;
parent_pool = pool_parent(parent_pool);
}
/*
* We can only hit this when test_pool is not a
* descendant of limit_pool.
*/
if (WARN_ON_ONCE(css == &limit_pool->cs->css))
break;
}
css = next_css;
found_descendant = false;
css_for_each_descendant_pre(css, &limit_pool->cs->css) {
dmemcg_iter = container_of(css, struct dmemcg_state, css);
found_pool = NULL;
list_for_each_entry_rcu(pool, &dmemcg_iter->pools, css_node) {
if (pool_parent(pool) == parent_pool) {
found_descendant = true;
if (pool->region == limit_pool->region) {
found_pool = pool;
break;
}
}
if (!found_descendant)
if (!found_pool)
continue;
page_counter_calculate_protection(
climit, &pool->cnt, true);
climit, &found_pool->cnt, true);
if (found_pool == test_pool)
break;
}
rcu_read_unlock();
}