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Andreas Gruenbacher aaa5ea0ec3 gfs2: Rework freeze / thaw logic 
[ Upstream commit b77b4a4815 ]

So far, at mount time, gfs2 would take the freeze glock in shared mode
and then immediately drop it again, turning it into a cached glock that
can be reclaimed at any time.  To freeze the filesystem cluster-wide,
the node initiating the freeze would take the freeze glock in exclusive
mode, which would cause the freeze glock's freeze_go_sync() callback to
run on each node.  There, gfs2 would freeze the filesystem and schedule
gfs2_freeze_func() to run.  gfs2_freeze_func() would re-acquire the
freeze glock in shared mode, thaw the filesystem, and drop the freeze
glock again.  The initiating node would keep the freeze glock held in
exclusive mode.  To thaw the filesystem, the initiating node would drop
the freeze glock again, which would allow gfs2_freeze_func() to resume
on all nodes, leaving the filesystem in the thawed state.

It turns out that in freeze_go_sync(), we cannot reliably and safely
freeze the filesystem.  This is primarily because the final unmount of a
filesystem takes a write lock on the s_umount rw semaphore before
calling into gfs2_put_super(), and freeze_go_sync() needs to call
freeze_super() which also takes a write lock on the same semaphore,
causing a deadlock.  We could work around this by trying to take an
active reference on the super block first, which would prevent unmount
from running at the same time.  But that can fail, and freeze_go_sync()
isn't actually allowed to fail.

To get around this, this patch changes the freeze glock locking scheme
as follows:

At mount time, each node takes the freeze glock in shared mode.  To
freeze a filesystem, the initiating node first freezes the filesystem
locally and then drops and re-acquires the freeze glock in exclusive
mode.  All other nodes notice that there is contention on the freeze
glock in their go_callback callbacks, and they schedule
gfs2_freeze_func() to run.  There, they freeze the filesystem locally
and drop and re-acquire the freeze glock before re-thawing the
filesystem.  This is happening outside of the glock state engine, so
there, we are allowed to fail.

From a cluster point of view, taking and immediately dropping a glock is
indistinguishable from taking the glock and only dropping it upon
contention, so this new scheme is compatible with the old one.

Thanks to Li Dong <lidong@vivo.com> for reporting a locking bug in
gfs2_freeze_func() in a previous version of this commit.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Stable-dep-of: f66af88e33 ("gfs2: Stop using gfs2_make_fs_ro for withdraw")
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2024-08-29 17:30:18 +02:00
arch s390/uv: Panic for set and remove shared access UVC errors 2024-08-29 17:30:16 +02:00
block block/mq-deadline: Fix the tag reservation code 2024-08-14 13:53:02 +02:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: aead,cipher - zeroize key buffer after use 2024-07-11 12:47:05 +02:00
Documentation smb3: fix setting SecurityFlags when encryption is required 2024-08-14 13:52:59 +02:00
drivers drm/amdgpu/jpeg2: properly set atomics vmid field 2024-08-29 17:30:16 +02:00
fs
include pid: Replace struct pid 1-element array with flex-array 2024-08-29 17:30:18 +02:00
init rust: SHADOW_CALL_STACK is incompatible with Rust 2024-08-11 12:35:59 +02:00
io_uring io_uring: fix io_match_task must_hold 2024-08-03 08:49:53 +02:00
ipc sysctl: treewide: drop unused argument ctl_table_root::set_ownership(table) 2024-08-11 12:35:51 +02:00
kernel pid: Replace struct pid 1-element array with flex-array 2024-08-29 17:30:18 +02:00
lib bitmap: introduce generic optimized bitmap_size() 2024-08-29 17:30:14 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: khugepaged: fix kernel BUG in hpage_collapse_scan_file() 2024-08-29 17:30:17 +02:00
net wifi: cfg80211: restrict NL80211_ATTR_TXQ_QUANTUM values 2024-08-19 06:00:07 +02:00
rust rust: macros: fix soundness issue in module! macro 2024-05-17 11:56:17 +02:00
samples work around gcc bugs with 'asm goto' with outputs 2024-02-23 09:12:28 +01:00
scripts kbuild: avoid build error when single DTB is turned into composite DTB 2024-08-03 08:49:48 +02:00
security selinux: fix potential counting error in avc_add_xperms_decision() 2024-08-29 17:30:15 +02:00
sound ALSA: usb-audio: Support Yamaha P-125 quirk entry 2024-08-29 17:30:13 +02:00
tools rtla/osnoise: Prevent NULL dereference in error handling 2024-08-29 17:30:15 +02:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-06-27 13:46:21 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add leah to 6.1 MAINTAINERS file 2024-05-17 11:56:16 +02:00
Makefile Linux 6.1.106 2024-08-19 06:00:07 +02:00
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.