<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux-stable.git/drivers/block, branch v5.3.16</title>
<subtitle>Linux kernel stable tree</subtitle>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/'/>
<entry>
<title>rsxx: add missed destroy_workqueue calls in remove</title>
<updated>2019-12-13T07:48:43+00:00</updated>
<author>
<name>Chuhong Yuan</name>
<email>hslester96@gmail.com</email>
</author>
<published>2019-11-13T06:38:47+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=7696b49eb96e06865c3f907e28d5a3f8b814c6c0'/>
<id>7696b49eb96e06865c3f907e28d5a3f8b814c6c0</id>
<content type='text'>
[ Upstream commit dcb77e4b274b8f13ac6482dfb09160cd2fae9a40 ]

The driver misses calling destroy_workqueue in remove like what is done
when probe fails.
Add the missed calls to fix it.

Signed-off-by: Chuhong Yuan &lt;hslester96@gmail.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[ Upstream commit dcb77e4b274b8f13ac6482dfb09160cd2fae9a40 ]

The driver misses calling destroy_workqueue in remove like what is done
when probe fails.
Add the missed calls to fix it.

Signed-off-by: Chuhong Yuan &lt;hslester96@gmail.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>rbd: silence bogus uninitialized warning in rbd_object_map_update_finish()</title>
<updated>2019-12-13T07:48:42+00:00</updated>
<author>
<name>Ilya Dryomov</name>
<email>idryomov@gmail.com</email>
</author>
<published>2019-11-13T11:07:15+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=94fb895537c41354da885bb3de2aa75d1e2feb72'/>
<id>94fb895537c41354da885bb3de2aa75d1e2feb72</id>
<content type='text'>
[ Upstream commit 633739b2fedb6617d782ca252797b7a8ad754347 ]

Some versions of gcc (so far 6.3 and 7.4) throw a warning:

  drivers/block/rbd.c: In function 'rbd_object_map_callback':
  drivers/block/rbd.c:2124:21: warning: 'current_state' may be used uninitialized in this function [-Wmaybe-uninitialized]
        (current_state == OBJECT_EXISTS &amp;&amp; state == OBJECT_EXISTS_CLEAN))
  drivers/block/rbd.c:2092:23: note: 'current_state' was declared here
    u8 state, new_state, current_state;
                          ^~~~~~~~~~~~~

It's bogus because all current_state accesses are guarded by
has_current_state.

Reported-by: kbuild test robot &lt;lkp@intel.com&gt;
Signed-off-by: Ilya Dryomov &lt;idryomov@gmail.com&gt;
Reviewed-by: Dongsheng Yang &lt;dongsheng.yang@easystack.cn&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[ Upstream commit 633739b2fedb6617d782ca252797b7a8ad754347 ]

Some versions of gcc (so far 6.3 and 7.4) throw a warning:

  drivers/block/rbd.c: In function 'rbd_object_map_callback':
  drivers/block/rbd.c:2124:21: warning: 'current_state' may be used uninitialized in this function [-Wmaybe-uninitialized]
        (current_state == OBJECT_EXISTS &amp;&amp; state == OBJECT_EXISTS_CLEAN))
  drivers/block/rbd.c:2092:23: note: 'current_state' was declared here
    u8 state, new_state, current_state;
                          ^~~~~~~~~~~~~

It's bogus because all current_state accesses are guarded by
has_current_state.

Reported-by: kbuild test robot &lt;lkp@intel.com&gt;
Signed-off-by: Ilya Dryomov &lt;idryomov@gmail.com&gt;
Reviewed-by: Dongsheng Yang &lt;dongsheng.yang@easystack.cn&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>block: drbd: remove a stray unlock in __drbd_send_protocol()</title>
<updated>2019-12-04T21:34:01+00:00</updated>
<author>
<name>Dan Carpenter</name>
<email>dan.carpenter@oracle.com</email>
</author>
<published>2019-11-07T07:48:47+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=900960e07966f4705b888778542bbb39c3703e7e'/>
<id>900960e07966f4705b888778542bbb39c3703e7e</id>
<content type='text'>
[ Upstream commit 8e9c523016cf9983b295e4bc659183d1fa6ef8e0 ]

There are two callers of this function and they both unlock the mutex so
this ends up being a double unlock.

Fixes: 44ed167da748 ("drbd: rcu_read_lock() and rcu_dereference() for tconn-&gt;net_conf")
Signed-off-by: Dan Carpenter &lt;dan.carpenter@oracle.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[ Upstream commit 8e9c523016cf9983b295e4bc659183d1fa6ef8e0 ]

There are two callers of this function and they both unlock the mutex so
this ends up being a double unlock.

Fixes: 44ed167da748 ("drbd: rcu_read_lock() and rcu_dereference() for tconn-&gt;net_conf")
Signed-off-by: Dan Carpenter &lt;dan.carpenter@oracle.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>nbd: prevent memory leak</title>
<updated>2019-11-29T09:08:01+00:00</updated>
<author>
<name>Navid Emamdoost</name>
<email>navid.emamdoost@gmail.com</email>
</author>
<published>2019-09-23T20:09:58+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=0f7f699019ddc3bee6d180c0de839ee6e89945bf'/>
<id>0f7f699019ddc3bee6d180c0de839ee6e89945bf</id>
<content type='text'>
commit 03bf73c315edca28f47451913177e14cd040a216 upstream.

In nbd_add_socket when krealloc succeeds, if nsock's allocation fail the
reallocted memory is leak. The correct behaviour should be assigning the
reallocted memory to config-&gt;socks right after success.

Reviewed-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Signed-off-by: Navid Emamdoost &lt;navid.emamdoost@gmail.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 03bf73c315edca28f47451913177e14cd040a216 upstream.

In nbd_add_socket when krealloc succeeds, if nsock's allocation fail the
reallocted memory is leak. The correct behaviour should be assigning the
reallocted memory to config-&gt;socks right after success.

Reviewed-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Signed-off-by: Navid Emamdoost &lt;navid.emamdoost@gmail.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>nbd:fix memory leak in nbd_get_socket()</title>
<updated>2019-11-29T09:07:43+00:00</updated>
<author>
<name>Sun Ke</name>
<email>sunke32@huawei.com</email>
</author>
<published>2019-11-19T06:09:11+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=2475eff09c2abf48594e030e7b077a48aa801ae0'/>
<id>2475eff09c2abf48594e030e7b077a48aa801ae0</id>
<content type='text'>
commit dff10bbea4be47bdb615b036c834a275b7c68133 upstream.

Before returning NULL, put the sock first.

Cc: stable@vger.kernel.org
Fixes: cf1b2326b734 ("nbd: verify socket is supported during setup")
Reviewed-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Reviewed-by: Mike Christie &lt;mchristi@redhat.com&gt;
Signed-off-by: Sun Ke &lt;sunke32@huawei.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit dff10bbea4be47bdb615b036c834a275b7c68133 upstream.

Before returning NULL, put the sock first.

Cc: stable@vger.kernel.org
Fixes: cf1b2326b734 ("nbd: verify socket is supported during setup")
Reviewed-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Reviewed-by: Mike Christie &lt;mchristi@redhat.com&gt;
Signed-off-by: Sun Ke &lt;sunke32@huawei.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>nbd: handle racing with error'ed out commands</title>
<updated>2019-11-10T10:34:29+00:00</updated>
<author>
<name>Josef Bacik</name>
<email>josef@toxicpanda.com</email>
</author>
<published>2019-10-21T19:56:28+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=0776cc4bf978d16a3c4b562d1cff5a20777e3329'/>
<id>0776cc4bf978d16a3c4b562d1cff5a20777e3329</id>
<content type='text'>
[ Upstream commit 7ce23e8e0a9cd38338fc8316ac5772666b565ca9 ]

We hit the following warning in production

print_req_error: I/O error, dev nbd0, sector 7213934408 flags 80700
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 25 PID: 32407 at lib/refcount.c:190 refcount_sub_and_test_checked+0x53/0x60
Workqueue: knbd-recv recv_work [nbd]
RIP: 0010:refcount_sub_and_test_checked+0x53/0x60
Call Trace:
 blk_mq_free_request+0xb7/0xf0
 blk_mq_complete_request+0x62/0xf0
 recv_work+0x29/0xa1 [nbd]
 process_one_work+0x1f5/0x3f0
 worker_thread+0x2d/0x3d0
 ? rescuer_thread+0x340/0x340
 kthread+0x111/0x130
 ? kthread_create_on_node+0x60/0x60
 ret_from_fork+0x1f/0x30
---[ end trace b079c3c67f98bb7c ]---

This was preceded by us timing out everything and shutting down the
sockets for the device.  The problem is we had a request in the queue at
the same time, so we completed the request twice.  This can actually
happen in a lot of cases, we fail to get a ref on our config, we only
have one connection and just error out the command, etc.

Fix this by checking cmd-&gt;status in nbd_read_stat.  We only change this
under the cmd-&gt;lock, so we are safe to check this here and see if we've
already error'ed this command out, which would indicate that we've
completed it as well.

Reviewed-by: Mike Christie &lt;mchristi@redhat.com&gt;
Signed-off-by: Josef Bacik &lt;josef@toxicpanda.com&gt;

Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[ Upstream commit 7ce23e8e0a9cd38338fc8316ac5772666b565ca9 ]

We hit the following warning in production

print_req_error: I/O error, dev nbd0, sector 7213934408 flags 80700
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 25 PID: 32407 at lib/refcount.c:190 refcount_sub_and_test_checked+0x53/0x60
Workqueue: knbd-recv recv_work [nbd]
RIP: 0010:refcount_sub_and_test_checked+0x53/0x60
Call Trace:
 blk_mq_free_request+0xb7/0xf0
 blk_mq_complete_request+0x62/0xf0
 recv_work+0x29/0xa1 [nbd]
 process_one_work+0x1f5/0x3f0
 worker_thread+0x2d/0x3d0
 ? rescuer_thread+0x340/0x340
 kthread+0x111/0x130
 ? kthread_create_on_node+0x60/0x60
 ret_from_fork+0x1f/0x30
---[ end trace b079c3c67f98bb7c ]---

This was preceded by us timing out everything and shutting down the
sockets for the device.  The problem is we had a request in the queue at
the same time, so we completed the request twice.  This can actually
happen in a lot of cases, we fail to get a ref on our config, we only
have one connection and just error out the command, etc.

Fix this by checking cmd-&gt;status in nbd_read_stat.  We only change this
under the cmd-&gt;lock, so we are safe to check this here and see if we've
already error'ed this command out, which would indicate that we've
completed it as well.

Reviewed-by: Mike Christie &lt;mchristi@redhat.com&gt;
Signed-off-by: Josef Bacik &lt;josef@toxicpanda.com&gt;

Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>nbd: protect cmd-&gt;status with cmd-&gt;lock</title>
<updated>2019-11-10T10:34:29+00:00</updated>
<author>
<name>Josef Bacik</name>
<email>josef@toxicpanda.com</email>
</author>
<published>2019-10-21T19:56:27+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=51c7037bf2765959768c261f5aae9118f8746ff7'/>
<id>51c7037bf2765959768c261f5aae9118f8746ff7</id>
<content type='text'>
[ Upstream commit de6346ecbc8f5591ebd6c44ac164e8b8671d71d7 ]

We already do this for the most part, except in timeout and clear_req.
For the timeout case we take the lock after we grab a ref on the config,
but that isn't really necessary because we're safe to touch the cmd at
this point, so just move the order around.

For the clear_req cause this is initiated by the user, so again is safe.

Reviewed-by: Mike Christie &lt;mchristi@redhat.com&gt;
Signed-off-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[ Upstream commit de6346ecbc8f5591ebd6c44ac164e8b8671d71d7 ]

We already do this for the most part, except in timeout and clear_req.
For the timeout case we take the lock after we grab a ref on the config,
but that isn't really necessary because we're safe to touch the cmd at
this point, so just move the order around.

For the clear_req cause this is initiated by the user, so again is safe.

Reviewed-by: Mike Christie &lt;mchristi@redhat.com&gt;
Signed-off-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>nbd: verify socket is supported during setup</title>
<updated>2019-11-06T12:08:49+00:00</updated>
<author>
<name>Mike Christie</name>
<email>mchristi@redhat.com</email>
</author>
<published>2019-10-17T21:27:34+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=4fa1cbd587ef967812f9d9f6ce46ec1dead7502c'/>
<id>4fa1cbd587ef967812f9d9f6ce46ec1dead7502c</id>
<content type='text'>
[ Upstream commit cf1b2326b734896734c6e167e41766f9cee7686a ]

nbd requires socket families to support the shutdown method so the nbd
recv workqueue can be woken up from its sock_recvmsg call. If the socket
does not support the callout we will leave recv works running or get hangs
later when the device or module is removed.

This adds a check during socket connection/reconnection to make sure the
socket being passed in supports the needed callout.

Reported-by: syzbot+24c12fa8d218ed26011a@syzkaller.appspotmail.com
Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs")
Tested-by: Richard W.M. Jones &lt;rjones@redhat.com&gt;
Signed-off-by: Mike Christie &lt;mchristi@redhat.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[ Upstream commit cf1b2326b734896734c6e167e41766f9cee7686a ]

nbd requires socket families to support the shutdown method so the nbd
recv workqueue can be woken up from its sock_recvmsg call. If the socket
does not support the callout we will leave recv works running or get hangs
later when the device or module is removed.

This adds a check during socket connection/reconnection to make sure the
socket being passed in supports the needed callout.

Reported-by: syzbot+24c12fa8d218ed26011a@syzkaller.appspotmail.com
Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs")
Tested-by: Richard W.M. Jones &lt;rjones@redhat.com&gt;
Signed-off-by: Mike Christie &lt;mchristi@redhat.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>nbd: fix possible sysfs duplicate warning</title>
<updated>2019-11-06T12:08:44+00:00</updated>
<author>
<name>Xiubo Li</name>
<email>xiubli@redhat.com</email>
</author>
<published>2019-09-19T06:14:27+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=1df6bb8ce8ababaee2d66add746235a73e5df2db'/>
<id>1df6bb8ce8ababaee2d66add746235a73e5df2db</id>
<content type='text'>
[ Upstream commit 862488105b84ca744b3d8ff131e0fcfe10644be1 ]

1. nbd_put takes the mutex and drops nbd-&gt;ref to 0. It then does
idr_remove and drops the mutex.

2. nbd_genl_connect takes the mutex. idr_find/idr_for_each fails
to find an existing device, so it does nbd_dev_add.

3. just before the nbd_put could call nbd_dev_remove or not finished
totally, but if nbd_dev_add try to add_disk, we can hit:

debugfs: Directory 'nbd1' with parent 'block' already present!

This patch will make sure all the disk add/remove stuff are done
by holding the nbd_index_mutex lock.

Reported-by: Mike Christie &lt;mchristi@redhat.com&gt;
Reviewed-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Signed-off-by: Xiubo Li &lt;xiubli@redhat.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[ Upstream commit 862488105b84ca744b3d8ff131e0fcfe10644be1 ]

1. nbd_put takes the mutex and drops nbd-&gt;ref to 0. It then does
idr_remove and drops the mutex.

2. nbd_genl_connect takes the mutex. idr_find/idr_for_each fails
to find an existing device, so it does nbd_dev_add.

3. just before the nbd_put could call nbd_dev_remove or not finished
totally, but if nbd_dev_add try to add_disk, we can hit:

debugfs: Directory 'nbd1' with parent 'block' already present!

This patch will make sure all the disk add/remove stuff are done
by holding the nbd_index_mutex lock.

Reported-by: Mike Christie &lt;mchristi@redhat.com&gt;
Reviewed-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Signed-off-by: Xiubo Li &lt;xiubli@redhat.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>zram: fix race between backing_dev_show and backing_dev_store</title>
<updated>2019-10-29T08:22:34+00:00</updated>
<author>
<name>Chenwandun</name>
<email>chenwandun@huawei.com</email>
</author>
<published>2019-10-19T03:20:14+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux-stable.git/commit/?id=b0c233e5d62da8ab481939f733d87cbd48c76904'/>
<id>b0c233e5d62da8ab481939f733d87cbd48c76904</id>
<content type='text'>
commit f7daefe4231e57381d92c2e2ad905a899c28e402 upstream.

CPU0:				       CPU1:
backing_dev_show		       backing_dev_store
    ......				   ......
    file = zram-&gt;backing_dev;
    down_read(&amp;zram-&gt;init_lock);	   down_read(&amp;zram-&gt;init_init_lock)
    file_path(file, ...);		   zram-&gt;backing_dev = backing_dev;
    up_read(&amp;zram-&gt;init_lock);		   up_read(&amp;zram-&gt;init_lock);

gets the value of zram-&gt;backing_dev too early in backing_dev_show, which
resultin the value being NULL at the beginning, and not NULL later.

backtrace:
  d_path+0xcc/0x174
  file_path+0x10/0x18
  backing_dev_show+0x40/0xb4
  dev_attr_show+0x20/0x54
  sysfs_kf_seq_show+0x9c/0x10c
  kernfs_seq_show+0x28/0x30
  seq_read+0x184/0x488
  kernfs_fop_read+0x5c/0x1a4
  __vfs_read+0x44/0x128
  vfs_read+0xa0/0x138
  SyS_read+0x54/0xb4

Link: http://lkml.kernel.org/r/1571046839-16814-1-git-send-email-chenwandun@huawei.com
Signed-off-by: Chenwandun &lt;chenwandun@huawei.com&gt;
Acked-by: Minchan Kim &lt;minchan@kernel.org&gt;
Cc: Sergey Senozhatsky &lt;sergey.senozhatsky.work@gmail.com&gt;
Cc: Jens Axboe &lt;axboe@kernel.dk&gt;
Cc: &lt;stable@vger.kernel.org&gt;	[4.14+]
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

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commit f7daefe4231e57381d92c2e2ad905a899c28e402 upstream.

CPU0:				       CPU1:
backing_dev_show		       backing_dev_store
    ......				   ......
    file = zram-&gt;backing_dev;
    down_read(&amp;zram-&gt;init_lock);	   down_read(&amp;zram-&gt;init_init_lock)
    file_path(file, ...);		   zram-&gt;backing_dev = backing_dev;
    up_read(&amp;zram-&gt;init_lock);		   up_read(&amp;zram-&gt;init_lock);

gets the value of zram-&gt;backing_dev too early in backing_dev_show, which
resultin the value being NULL at the beginning, and not NULL later.

backtrace:
  d_path+0xcc/0x174
  file_path+0x10/0x18
  backing_dev_show+0x40/0xb4
  dev_attr_show+0x20/0x54
  sysfs_kf_seq_show+0x9c/0x10c
  kernfs_seq_show+0x28/0x30
  seq_read+0x184/0x488
  kernfs_fop_read+0x5c/0x1a4
  __vfs_read+0x44/0x128
  vfs_read+0xa0/0x138
  SyS_read+0x54/0xb4

Link: http://lkml.kernel.org/r/1571046839-16814-1-git-send-email-chenwandun@huawei.com
Signed-off-by: Chenwandun &lt;chenwandun@huawei.com&gt;
Acked-by: Minchan Kim &lt;minchan@kernel.org&gt;
Cc: Sergey Senozhatsky &lt;sergey.senozhatsky.work@gmail.com&gt;
Cc: Jens Axboe &lt;axboe@kernel.dk&gt;
Cc: &lt;stable@vger.kernel.org&gt;	[4.14+]
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

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