From: Dan Schatzberg <schatzberg.dan@gmail.com>
To: unlisted-recipients:; (no To-header on input)
Cc: Jens Axboe <axboe@kernel.dk>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>, Qian Cai <cai@lca.pw>,
linux-block@vger.kernel.org (open list:BLOCK LAYER),
linux-mm@kvack.org (open list:CONTROL GROUP - MEMORY RESOURCE
CONTROLLER (MEMCG)), linux-kernel@vger.kernel.org (open list),
Dan Schatzberg <schatzberg.dan@gmail.com>
Subject: [PATCH] loop: Fix irq lock ordering bug
Date: Fri, 28 Feb 2020 11:18:47 -0500 [thread overview]
Message-ID: <20200228161847.28107-1-schatzberg.dan@gmail.com> (raw)
"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.
Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>
---
drivers/block/loop.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index eb766db48685..366658e60064 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -768,12 +768,18 @@ static ssize_t loop_attr_backing_file_show(struct loop_device *lo, char *buf)
{
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 {
--
2.17.1
reply other threads:[~2020-02-28 16:19 UTC|newest]
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