The quilt patch titled
Subject: mm: memcontrol: fix potential oom_lock recursion deadlock
has been removed from the -mm tree. Its filename was
mm-memcontrol-fix-potential-oom_lock-recursion-deadlock.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Subject: mm: memcontrol: fix potential oom_lock recursion deadlock
Date: Fri, 22 Jul 2022 19:45:39 +0900
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@xxxxxxxxxxxxxxxxxxx
Fixes: c8713d0b23123759 ("mm: memcontrol: dump memory.stat during cgroup OOM")
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+2d2aeadc6ce1e1f11d45@xxxxxxxxxxxxxxxxxxxxxxxxx>
Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 22 +++++++++-------------
1 file changed, 9 insertions(+), 13 deletions(-)
--- a/mm/memcontrol.c~mm-memcontrol-fix-potential-oom_lock-recursion-deadlock
+++ a/mm/memcontrol.c
@@ -1490,14 +1490,12 @@ static const unsigned int memcg_vm_event
#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 m
/* 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
*/
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
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(stru
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;
_
Patches currently in -mm which might be from penguin-kernel@xxxxxxxxxxxxxxxxxxx are
