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Hou Tao 68c9417b19 nbd: do del_gendisk() asynchronously for NBD_DESTROY_ON_DISCONNECT 
Now open_mutex is used to synchronize partition operations (e.g,
blk_drop_partitions() and blkdev_reread_part()), however it makes
nbd driver broken, because nbd may call del_gendisk() in nbd_release()
or nbd_genl_disconnect() if NBD_CFLAG_DESTROY_ON_DISCONNECT is enabled,
and deadlock occurs, as shown below:

// AB-BA dead-lock
nbd_genl_disconnect            blkdev_open
  nbd_disconnect_and_put
                                 lock bd_mutex
  // last ref
  nbd_put
    lock nbd_index_mutex
      del_gendisk
                                   nbd_open
                                     try lock nbd_index_mutex
        try lock bd_mutex

 or

// AA dead-lock
nbd_release
  lock bd_mutex
    nbd_put
      try lock bd_mutex

Instead of fixing block layer (e.g, introduce another lock), fixing
the nbd driver to call del_gendisk() in a kworker when
NBD_DESTROY_ON_DISCONNECT is enabled. When NBD_DESTROY_ON_DISCONNECT
is disabled, nbd device will always be destroy through module removal,
and there is no risky of deadlock.

To ensure the reuse of nbd index succeeds, moving the calling of
idr_remove() after del_gendisk(), so if the reused index is not found
in nbd_index_idr, the old disk must have been deleted. And reusing
the existing destroy_complete mechanism to ensure nbd_genl_connect()
will wait for the completion of del_gendisk().

Also adding a new workqueue for nbd removal, so nbd_cleanup()
can ensure all removals complete before exits.

Reported-by: syzbot+0fe7752e52337864d29b@syzkaller.appspotmail.com
Fixes: c76f48eb5c ("block: take bd_mutex around delete_partitions in del_gendisk")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210811124428.2368491-2-hch@lst.de
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-08-13 14:17:16 -06:00
arch block: remove cmdline-parser.c 2021-08-02 13:37:28 -06:00
block block: remove blk-mq-sysfs dead code 2021-08-02 13:37:29 -06:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2021-07-09 11:00:44 -07:00
Documentation block: export diskseq in sysfs 2021-08-02 13:37:28 -06:00
drivers nbd: do del_gendisk() asynchronously for NBD_DESTROY_ON_DISCONNECT 2021-08-13 14:17:16 -06:00
fs block: remove bdput 2021-08-02 13:37:28 -06:00
include block: add a helper to raise a media changed event 2021-08-02 13:37:28 -06:00
init Revert "mm/slub: use stackdepot to save stack trace in objects" 2021-07-17 13:27:00 -07:00
ipc Merge branch 'akpm' (patches from Andrew) 2021-07-02 12:08:10 -07:00
kernel Networking fixes for 5.14-rc4, including fixes from bpf, can, WiFi (mac80211) 2021-07-30 16:01:36 -07:00
lib lib/test_string.c: move string selftest in the Runtime Testing menu 2021-07-30 10:14:39 -07:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook() 2021-07-30 10:14:39 -07:00
net Networking fixes for 5.14-rc4, including fixes from bpf, can, WiFi (mac80211) 2021-07-30 16:01:36 -07:00
samples Networking fixes for 5.14-rc2, including fixes from bpf and netfilter. 2021-07-14 09:24:32 -07:00
scripts Kbuild fixes for v5.14 2021-07-18 11:10:30 -07:00
security asm-generic/unaligned: Unify asm/unaligned.h around struct helper 2021-07-02 12:43:40 -07:00
sound sound fixes for 5.14-rc3 2021-07-23 09:58:23 -07:00
tools perf tools fixes for v5.14: 2nd batch 2021-08-01 12:25:30 -07:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: add missing compat KVM_CLEAR_DIRTY_LOG 2021-07-27 16:59:01 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap m68k updates for v5.14 2021-06-28 14:01:03 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Networking fixes for 5.14-rc4, including fixes from bpf, can, WiFi (mac80211) 2021-07-30 16:01:36 -07:00
Makefile Linux 5.14-rc4 2021-08-01 17:04:17 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.