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Xiao Ni fe272570d0 md: Set prev_flush_start and flush_bio in an atomic way 
commit dc5d17a3c3 upstream.

One customer reports a crash problem which causes by flush request. It
triggers a warning before crash.

        /* new request after previous flush is completed */
        if (ktime_after(req_start, mddev->prev_flush_start)) {
                WARN_ON(mddev->flush_bio);
                mddev->flush_bio = bio;
                bio = NULL;
        }

The WARN_ON is triggered. We use spin lock to protect prev_flush_start and
flush_bio in md_flush_request. But there is no lock protection in
md_submit_flush_data. It can set flush_bio to NULL first because of
compiler reordering write instructions.

For example, flush bio1 sets flush bio to NULL first in
md_submit_flush_data. An interrupt or vmware causing an extended stall
happen between updating flush_bio and prev_flush_start. Because flush_bio
is NULL, flush bio2 can get the lock and submit to underlayer disks. Then
flush bio1 updates prev_flush_start after the interrupt or extended stall.

Then flush bio3 enters in md_flush_request. The start time req_start is
behind prev_flush_start. The flush_bio is not NULL(flush bio2 hasn't
finished). So it can trigger the WARN_ON now. Then it calls INIT_WORK
again. INIT_WORK() will re-initialize the list pointers in the
work_struct, which then can result in a corrupted work list and the
work_struct queued a second time. With the work list corrupted, it can
lead in invalid work items being used and cause a crash in
process_one_work.

We need to make sure only one flush bio can be handled at one same time.
So add spin lock in md_submit_flush_data to protect prev_flush_start and
flush_bio in an atomic way.

Reviewed-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2021-02-10 09:29:22 +01:00
arch x86/apic: Add extra serialization for non-serializing MSRs 2021-02-10 09:29:22 +01:00
block blk-mq: test QUEUE_FLAG_HCTX_ACTIVE for sbitmap_shared in hctx_may_queue 2021-02-03 23:28:44 +01:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: xor - Fix divide error in do_xor_speed() 2021-01-27 11:54:52 +01:00
Documentation ovl: implement volatile-specific fsync error behaviour 2021-02-10 09:29:16 +01:00
drivers md: Set prev_flush_start and flush_bio in an atomic way 2021-02-10 09:29:22 +01:00
fs mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page 2021-02-10 09:29:20 +01:00
include mm/vmalloc: separate put pages and flush VM flags 2021-02-10 09:29:21 +01:00
init fgraph: Initialize tracing_graph_pause at task creation 2021-02-10 09:29:16 +01:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel genirq/msi: Activate Multi-MSI early when MSI_FLAG_ACTIVATE_EARLY is set 2021-02-10 09:29:17 +01:00
lib iov_iter: fix the uaccess area in copy_compat_iovec_from_user 2021-01-27 11:55:09 +01:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm/filemap: add missing mem_cgroup_uncharge() to __add_to_page_cache_locked() 2021-02-10 09:29:21 +01:00
net mac80211: fix station rate table updates on assoc 2021-02-10 09:29:16 +01:00
samples samples/bpf: Fix possible hang in xdpsock with multiple threads 2020-12-30 11:53:49 +01:00
scripts scripts: use pkg-config to locate libcrypto 2021-02-10 09:29:17 +01:00
security dump_common_audit_data(): fix racy accesses to ->d_name 2021-01-19 18:27:29 +01:00
sound ALSA: hda: Add Cometlake-R PCI ID 2021-02-07 15:37:15 +01:00
tools objtool: Don't fail the kernel build on fatal errors 2021-02-07 15:37:17 +01:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt KVM: Forbid the use of tagged userspace addresses for memslots 2021-02-03 23:28:41 +01:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.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: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
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 Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-10 15:30:13 -08:00
Makefile x86/build: Disable CET instrumentation in the kernel 2021-02-10 09:29:21 +01:00
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.