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Josef Bacik 4e18c827d6 btrfs: wait for actual caching progress during allocation 
commit fc1f91b923 upstream.

Recently we've been having mysterious hangs while running generic/475 on
the CI system.  This turned out to be something like this:

  Task 1
  dmsetup suspend --nolockfs
  -> __dm_suspend
   -> dm_wait_for_completion
    -> dm_wait_for_bios_completion
     -> Unable to complete because of IO's on a plug in Task 2

  Task 2
  wb_workfn
  -> wb_writeback
   -> blk_start_plug
    -> writeback_sb_inodes
     -> Infinite loop unable to make an allocation

  Task 3
  cache_block_group
  ->read_extent_buffer_pages
   ->Waiting for IO to complete that can't be submitted because Task 1
     suspended the DM device

The problem here is that we need Task 2 to be scheduled completely for
the blk plug to flush.  Normally this would happen, we normally wait for
the block group caching to finish (Task 3), and this schedule would
result in the block plug flushing.

However if there's enough free space available from the current caching
to satisfy the allocation we won't actually wait for the caching to
complete.  This check however just checks that we have enough space, not
that we can make the allocation.  In this particular case we were trying
to allocate 9MiB, and we had 10MiB of free space, but we didn't have
9MiB of contiguous space to allocate, and thus the allocation failed and
we looped.

We specifically don't cycle through the FFE loop until we stop finding
cached block groups because we don't want to allocate new block groups
just because we're caching, so we short circuit the normal loop once we
hit LOOP_CACHING_WAIT and we found a caching block group.

This is normally fine, except in this particular case where the caching
thread can't make progress because the DM device has been suspended.

Fix this by not only waiting for free space to >= the amount of space we
want to allocate, but also that we make some progress in caching from
the time we start waiting.  This will keep us from busy looping when the
caching is taking a while but still theoretically has enough space for
us to allocate from, and fixes this particular case by forcing us to
actually sleep and wait for forward progress, which will flush the plug.

With this fix we're no longer hanging with generic/475.

CC: stable@vger.kernel.org # 6.1+
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2023-08-16 18:27:29 +02:00
arch x86: Move gds_ucode_mitigated() declaration to header 2023-08-16 18:27:25 +02:00
block blk-mq: Fix stall due to recursive flush plug 2023-08-03 10:23:48 +02:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: jitter - correct health test during initialization 2023-07-19 16:21:42 +02:00
Documentation iommu/arm-smmu-v3: Document nesting-related errata 2023-08-11 12:08:09 +02:00
drivers gpio: sim: mark the GPIO chip as a one that can sleep 2023-08-16 18:27:29 +02:00
fs btrfs: wait for actual caching progress during allocation 2023-08-16 18:27:29 +02:00
include wifi: cfg80211: fix sband iftype data lookup for AP_VLAN 2023-08-16 18:27:27 +02:00
init x86/mm: Initialize text poking earlier 2023-08-08 20:03:49 +02:00
io_uring io_uring: correct check for O_TMPFILE 2023-08-16 18:27:24 +02:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel bpf, cpumap: Make sure kthread is running before map update returns 2023-08-11 12:08:23 +02:00
lib debugobjects: Recheck debug_objects_enabled before reporting 2023-08-11 12:08:23 +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: kmem: fix a NULL pointer dereference in obj_stock_flush_required() 2023-08-11 12:08:23 +02:00
net nexthop: Fix infinite nexthop bucket dump when using maximum nexthop ID 2023-08-16 18:27:28 +02:00
rust rust: allocator: Prevent mis-aligned allocation 2023-08-11 12:08:18 +02:00
samples samples: ftrace: Save required argument registers in sample trampolines 2023-07-23 13:49:44 +02:00
scripts gcc-plugins: Reorganize gimple includes for GCC 13 2023-08-16 18:27:20 +02:00
security security: keys: Modify mismatched function name 2023-07-27 08:50:43 +02:00
sound ASoC: wm8904: Fill the cache for WM8904_ADC_TEST_0 register 2023-08-03 10:24:16 +02:00
tools nexthop: Fix infinite nexthop bucket dump when using maximum nexthop ID 2023-08-16 18:27:28 +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: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-08-03 10:24:08 +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 smb: move client and server files to common directory fs/smb 2023-06-28 11:12:40 +02:00
Makefile Linux 6.1.45 2023-08-11 12:08:27 +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.