+ loop-use-worker-per-cgroup-instead-of-kworker-fix-2.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: loop: fix irq lock ordering bug
has been added to the -mm tree.  Its filename is
     loop-use-worker-per-cgroup-instead-of-kworker-fix-2.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/loop-use-worker-per-cgroup-instead-of-kworker-fix-2.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/loop-use-worker-per-cgroup-instead-of-kworker-fix-2.patch

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------------------------------------------------------
From: Dan Schatzberg <schatzberg.dan@gmail.com>
Subject: loop: fix irq lock ordering bug

"loop: Use worker per cgroup instead of kworker" in patch series "Charge
loop device i/o to issuing cgroup", v3.  introduced a lock ordering bug. 
The previously existing lo->lo_lock was always acquired as spin_lock_irq
but never actually used in irq context.  The above patch started to use
this lock in irq context which triggered a lockdep warning on sysfs
reading.

Fix this by executing file_path outside of the lock.

Link: http://lkml.kernel.org/r/20200228161847.28107-1-schatzberg.dan@gmail.com
Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Chris Down <chris@chrisdown.name>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/block/loop.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/block/loop.c~loop-use-worker-per-cgroup-instead-of-kworker-fix-2
+++ a/drivers/block/loop.c
@@ -776,12 +776,18 @@ static ssize_t loop_attr_backing_file_sh
 {
 	ssize_t ret;
 	char *p = NULL;
+	struct file *filp = NULL;
 
 	spin_lock_irq(&lo->lo_lock);
 	if (lo->lo_backing_file)
-		p = file_path(lo->lo_backing_file, buf, PAGE_SIZE - 1);
+		filp = get_file(lo->lo_backing_file);
 	spin_unlock_irq(&lo->lo_lock);
 
+	if (filp) {
+		p = file_path(filp, buf, PAGE_SIZE - 1);
+		fput(filp);
+	}
+
 	if (IS_ERR_OR_NULL(p))
 		ret = PTR_ERR(p);
 	else {
_

Patches currently in -mm which might be from schatzberg.dan@gmail.com are

loop-use-worker-per-cgroup-instead-of-kworker.patch
loop-use-worker-per-cgroup-instead-of-kworker-fix-2.patch
mm-charge-active-memcg-when-no-mm-is-set.patch
loop-charge-i-o-to-mem-and-blk-cg.patch