b9a41d21dc
The following BUG_ON was hit when testing repeat creation and removal of
DM devices:
kernel BUG at drivers/md/dm.c:2919!
CPU: 7 PID: 750 Comm: systemd-udevd Not tainted 4.1.44
Call Trace:
[<ffffffff81649e8b>] dm_get_from_kobject+0x34/0x3a
[<ffffffff81650ef1>] dm_attr_show+0x2b/0x5e
[<ffffffff817b46d1>] ? mutex_lock+0x26/0x44
[<ffffffff811df7f5>] sysfs_kf_seq_show+0x83/0xcf
[<ffffffff811de257>] kernfs_seq_show+0x23/0x25
[<ffffffff81199118>] seq_read+0x16f/0x325
[<ffffffff811de994>] kernfs_fop_read+0x3a/0x13f
[<ffffffff8117b625>] __vfs_read+0x26/0x9d
[<ffffffff8130eb59>] ? security_file_permission+0x3c/0x44
[<ffffffff8117bdb8>] ? rw_verify_area+0x83/0xd9
[<ffffffff8117be9d>] vfs_read+0x8f/0xcf
[<ffffffff81193e34>] ? __fdget_pos+0x12/0x41
[<ffffffff8117c686>] SyS_read+0x4b/0x76
[<ffffffff817b606e>] system_call_fastpath+0x12/0x71
The bug can be easily triggered, if an extra delay (e.g. 10ms) is added
between the test of DMF_FREEING & DMF_DELETING and dm_get() in
dm_get_from_kobject().
To fix it, we need to ensure the test of DMF_FREEING & DMF_DELETING and
dm_get() are done in an atomic way, so _minor_lock is used.
The other callers of dm_get() have also been checked to be OK: some
callers invoke dm_get() under _minor_lock, some callers invoke it under
_hash_lock, and dm_start_request() invoke it after increasing
md->open_count.
Cc: stable@vger.kernel.org
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.