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Halil Pasic ed8b06a0eb s390/cio: make ccw_device_dma_* more robust 
commit ad9a145172 upstream.

Since commit 48720ba568 ("virtio/s390: use DMA memory for ccw I/O and
classic notifiers") we were supposed to make sure that
virtio_ccw_release_dev() completes before the ccw device and the
attached dma pool are torn down, but unfortunately we did not.  Before
that commit it used to be OK to delay cleaning up the memory allocated
by virtio-ccw indefinitely (which isn't really intuitive for guys used
to destruction happens in reverse construction order), but now we
trigger a BUG_ON if the genpool is destroyed before all memory allocated
from it is deallocated. Which brings down the guest. We can observe this
problem, when unregister_virtio_device() does not give up the last
reference to the virtio_device (e.g. because a virtio-scsi attached scsi
disk got removed without previously unmounting its previously mounted
partition).

To make sure that the genpool is only destroyed after all the necessary
freeing is done let us take a reference on the ccw device on each
ccw_device_dma_zalloc() and give it up on each ccw_device_dma_free().

Actually there are multiple approaches to fixing the problem at hand
that can work. The upside of this one is that it is the safest one while
remaining simple. We don't crash the guest even if the driver does not
pair allocations and frees. The downside is the reference counting
overhead, that the reference counting for ccw devices becomes more
complex, in a sense that we need to pair the calls to the aforementioned
functions for it to be correct, and that if we happen to leak, we leak
more than necessary (the whole ccw device instead of just the genpool).

Some alternatives to this approach are taking a reference in
virtio_ccw_online() and giving it up in virtio_ccw_release_dev() or
making sure virtio_ccw_release_dev() completes its work before
virtio_ccw_remove() returns. The downside of these approaches is that
these are less safe against programming errors.

Cc: <stable@vger.kernel.org> # v5.3
Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Fixes: 48720ba568 ("virtio/s390: use DMA memory for ccw I/O and classic notifiers")
Reported-by: bfu@redhat.com
Reviewed-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-11-18 19:17:18 +01:00
arch s390/cpumf: cpum_cf PMU displays invalid value after hotplug remove 2021-11-18 19:17:17 +01:00
block block: Hold invalidate_lock in BLKRESETZONE ioctl 2021-11-18 19:17:15 +01:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto crypto: pcrypt - Delay write to padata->info 2021-11-18 19:16:44 +01:00
Documentation fscrypt: allow 256-bit master keys with AES-256-XTS 2021-11-18 19:16:11 +01:00
drivers s390/cio: make ccw_device_dma_* more robust 2021-11-18 19:17:18 +01:00
fs mm, thp: fix incorrect unmap behavior for private pages 2021-11-18 19:17:17 +01:00
include net, neigh: Enable state migration between NUD_PERMANENT and NTF_USE 2021-11-18 19:17:16 +01:00
init init: make unknown command line param message clearer 2021-11-18 19:17:11 +01:00
ipc ipc: remove memcg accounting for sops objects in do_semtimedop() 2021-09-14 10:22:11 -07:00
kernel posix-cpu-timers: Clear task::posix_cputimers_work in copy_process() 2021-11-18 19:17:14 +01:00
lib dyndbg: make dyndbg a known cli param 2021-11-18 19:16:52 +01:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm, oom: do not trigger out_of_memory from the #PF 2021-11-18 19:17:16 +01:00
net 9p/net: fix missing error check in p9_check_errors 2021-11-18 19:17:16 +01:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-18 19:16:42 +01:00
scripts leaking_addresses: Always print a trailing newline 2021-11-18 19:16:16 +01:00
security apparmor: fix error check 2021-11-18 19:16:58 +01:00
sound ALSA: memalloc: Catch call with NULL snd_dma_buffer pointer 2021-11-18 19:17:08 +01:00
tools selftests/net: udpgso_bench_rx: fix port argument 2021-11-18 19:17:13 +01:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: Remove tlbs_dirty 2021-09-23 11:01:12 -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 mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
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 drm fixes for 5.15 final 2021-10-28 12:17:01 -07:00
Makefile Linux 5.15.2 2021-11-12 15:05:52 +01:00
README

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.