Commit 68aaee14 authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Andrew Morton
Browse files

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: c8713d0b ("mm: memcontrol: dump memory.stat during cgroup OOM")
Signed-off-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: default avatarsyzbot <syzbot+2d2aeadc6ce1e1f11d45@syzkaller.appspotmail.com>
Suggested-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarMichal 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 65974cb9

mm/memcontrol.c

+9 −13
Original line number Diff line number Diff line
@@ -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;