linux/drivers/s390
Gerald Schaefer 1378a68344 s390/dcssblk: fix possible deadlock in remove vs. per-device attributes
dcssblk_remove_store() holds the dcssblk_devices_sem semaphore while
calling device_unregister(), which in turn tries to acquire the kernfs
kn->dev_map rwsem for the device sysfs subtree. The same rwsem is also
acquired when using the per-device sysfs attributes in the device sub-tree,
and the attribute handlers then also acquire the dcssblk_devices_sem.

This can lead to a deadlock when removing a DCSS while concurrently
reading from / writing to one of its sysfs attributes. The following
lockdep warning hinted towards the issue (CPU0 = dcssblk_remove_store,
CPU1 = dcssblk_shared_store):

[   76.496047]  Possible unsafe locking scenario:

[   76.496054]        CPU0                    CPU1
[   76.496059]        ----                    ----
[   76.496087]   lock(&dcssblk_devices_sem);
[   76.496090]                                lock(s_active#175);
[   76.496106]                                lock(&dcssblk_devices_sem);
[   76.496110]   lock(s_active#175);
[   76.496115]
 *** DEADLOCK ***

Fix this by releasing the dcssblk_devices_sem semaphore, which only
protects internal DCSS data, before calling device_unregister().

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2016-04-15 18:01:44 +02:00
..
block s390/dcssblk: fix possible deadlock in remove vs. per-device attributes 2016-04-15 18:01:44 +02:00
char TTY/Serial patches for 4.6-rc1 2016-03-17 13:53:25 -07:00
cio s390: Use pr_warn instead of pr_warning 2016-03-07 13:12:04 +01:00
crypto s390/zcrypt: Fix cryptographic device id in kernel messages 2016-01-26 12:46:58 +01:00
net s390: Use pr_warn instead of pr_warning 2016-03-07 13:12:04 +01:00
scsi Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-09-03 15:46:07 -07:00
virtio virtio/s390: size of SET_IND payload 2016-03-02 18:08:59 +02:00
Makefile virtio/s390: rename drivers/s390/kvm -> drivers/s390/virtio 2015-07-07 14:27:06 +03:00