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@xxxxxxxxx>
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@xxxxxxxxx
Signed-off-by: Dan Schatzberg <schatzberg.dan@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Chris Down <chris@xxxxxxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>,
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxx 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
