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authorTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>2022-07-22 19:45:39 +0900
committerakpm <akpm@linux-foundation.org>2022-07-29 18:07:18 -0700
commit68aaee147e597b495622b7c9038e5922c7c61f57 (patch)
tree2da6862990dfea13856ad34b55e41e2ab1d6c1ca /mm/memcontrol.c
parent65974cb9107d9c6da18cefda22f84aeabc638b16 (diff)
mm: memcontrol: fix potential oom_lock recursion deadlock
syzbot is reporting GFP_KERNEL allocation with oom_lock held when reporting memcg OOM [1]. If this allocation triggers the global OOM situation then the system can livelock because the GFP_KERNEL allocation with oom_lock held cannot trigger the global OOM killer because __alloc_pages_may_oom() fails to hold oom_lock. Fix this problem by removing the allocation from memory_stat_format() completely, and pass static buffer when calling from memcg OOM path. Note that the caller holding filesystem lock was the trigger for syzbot to report this locking dependency. Doing GFP_KERNEL allocation with filesystem lock held can deadlock the system even without involving OOM situation. Link: https://syzkaller.appspot.com/bug?extid=2d2aeadc6ce1e1f11d45 [1] Link: https://lkml.kernel.org/r/86afb39f-8c65-bec2-6cfc-c5e3cd600c0b@I-love.SAKURA.ne.jp Fixes: c8713d0b23123759 ("mm: memcontrol: dump memory.stat during cgroup OOM") Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Reported-by: syzbot <syzbot+2d2aeadc6ce1e1f11d45@syzkaller.appspotmail.com> Suggested-by: Michal Hocko <mhocko@suse.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Shakeel Butt <shakeelb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
-rw-r--r--mm/memcontrol.c22
1 files changed, 9 insertions, 13 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c65751ab4516..b69979c9ced5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1490,14 +1490,12 @@ static const unsigned int memcg_vm_event_stat[] = {
#endif
};
-static char *memory_stat_format(struct mem_cgroup *memcg)
+static void memory_stat_format(struct mem_cgroup *memcg, char *buf, int bufsize)
{
struct seq_buf s;
int i;
- seq_buf_init(&s, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
- if (!s.buffer)
- return NULL;
+ seq_buf_init(&s, buf, bufsize);
/*
* Provide statistics on the state of the memory subsystem as
@@ -1539,8 +1537,6 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
/* The above should easily fit into one page */
WARN_ON_ONCE(seq_buf_has_overflowed(&s));
-
- return s.buffer;
}
#define K(x) ((x) << (PAGE_SHIFT-10))
@@ -1576,7 +1572,10 @@ void mem_cgroup_print_oom_context(struct mem_cgroup *memcg, struct task_struct *
*/
void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
{
- char *buf;
+ /* Use static buffer, for the caller is holding oom_lock. */
+ static char buf[PAGE_SIZE];
+
+ lockdep_assert_held(&oom_lock);
pr_info("memory: usage %llukB, limit %llukB, failcnt %lu\n",
K((u64)page_counter_read(&memcg->memory)),
@@ -1597,11 +1596,8 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg)
pr_info("Memory cgroup stats for ");
pr_cont_cgroup_path(memcg->css.cgroup);
pr_cont(":");
- buf = memory_stat_format(memcg);
- if (!buf)
- return;
+ memory_stat_format(memcg, buf, sizeof(buf));
pr_info("%s", buf);
- kfree(buf);
}
/*
@@ -6405,11 +6401,11 @@ static int memory_events_local_show(struct seq_file *m, void *v)
static int memory_stat_show(struct seq_file *m, void *v)
{
struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
- char *buf;
+ char *buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
- buf = memory_stat_format(memcg);
if (!buf)
return -ENOMEM;
+ memory_stat_format(memcg, buf, PAGE_SIZE);
seq_puts(m, buf);
kfree(buf);
return 0;